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This Ecma Standard defines the ECMAScript 2015 Language. It is the sixth edition of the ECMAScript Language Specification. Since publication of the first edition in 1997, ECMAScript has grown to be one of the world’s most widely used general purpose programming languages. It is best known as the language embedded in web browsers but has also been widely adopted for server and embedded applications. The sixth edition is the most extensive update to ECMAScript since the publication of the first edition in 1997.
Goals for ECMAScript 2015 include providing better support for large applications, library creation, and for use of ECMAScript as a compilation target for other languages. Some of its major enhancements include modules, class declarations, lexical block scoping, iterators and generators, promises for asynchronous programming, destructuring patterns, and proper tail calls. The ECMAScript library of built-ins has been expanded to support additional data abstractions including maps, sets, and arrays of binary numeric values as well as additional support for Unicode supplemental characters in strings and regular expressions. The built-ins are now extensible via subclassing.
ECMAScript is based on several originating technologies, the most well-known being JavaScript (Netscape) and JScript (Microsoft). The language was invented by Brendan Eich at Netscape and first appeared in that company’s Navigator 2.0 browser. It has appeared in all subsequent browsers from Netscape and in all browsers from Microsoft starting with Internet Explorer 3.0.
The development of the ECMAScript Language Specification started in November 1996. The first edition of this Ecma Standard was adopted by the Ecma General Assembly of June 1997.
That Ecma Standard was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international standard ISO/IEC 16262, in April 1998. The Ecma General Assembly of June 1998 approved the second edition of ECMA-262 to keep it fully aligned with ISO/IEC 16262. Changes between the first and the second edition are editorial in nature.
The third edition of the Standard introduced powerful regular expressions, better string handling, new control statements, try/catch exception handling, tighter definition of errors, formatting for numeric output and minor changes in anticipation future language growth. The third edition of the ECMAScript standard was adopted by the Ecma General Assembly of December 1999 and published as ISO/IEC 16262:2002 in June 2002.
After publication of the third edition, ECMAScript achieved massive adoption in conjunction with the World Wide Web where it has become the programming language that is supported by essentially all web browsers. Significant work was done to develop a fourth edition of ECMAScript. However, that work was not completed and not published as the fourth edition of ECMAScript but some of it was incorporated into the development of the sixth edition.
The fifth edition of ECMAScript (published as ECMA-262 5th edition) codified de facto interpretations of the language specification that have become common among browser implementations and added support for new features that had emerged since the publication of the third edition. Such features include accessor properties, reflective creation and inspection of objects, program control of property attributes, additional array manipulation functions, support for the JSON object encoding format, and a strict mode that provides enhanced error checking and program security. The Fifth Edition was adopted by the Ecma General Assembly of December 2009.
The fifth Edition was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international standard ISO/IEC 16262:2011. Edition 5.1 of the ECMAScript Standard incorporated minor corrections and is the same text as ISO/IEC 16262:2011. The 5.1 Edition was adopted by the Ecma General Assembly of June 2011.
Focused development of the sixth edition started in 2009, as the fifth edition was being prepared for publication. However, this was preceded by significant experimentation and language enhancement design efforts dating to the publication of the third edition in 1999. In a very real sense, the completion of the sixth edition is the culmination of a fifteen year effort.
Dozens of individuals representing many organizations have made very significant contributions within Ecma TC39 to the development of this edition and to the prior editions. In addition, a vibrant informal community has emerged supporting TC39’s ECMAScript efforts. This community has reviewed numerous drafts, filed thousands of bug reports, performed implementation experiments, contributed test suites, and educated the world-wide developer community about ECMAScript. Unfortunately, it is impossible to identify and acknowledge every person and organization who has contributed to this effort.
New uses and requirements for ECMAScript continue to emerge. The sixth edition provides the foundation for regular, incremental language and library enhancements.
Allen Wirfs-Brock
ECMA-262, 6th Edition Project Editor
This Ecma Standard has been adopted by the General Assembly of June 2015.
This Standard defines the ECMAScript 2015 general purpose programming language.
A conforming implementation of ECMAScript must provide and support all the types, values, objects, properties, functions, and program syntax and semantics described in this specification.
A conforming implementation of ECMAScript must interpret source text input in conformance with the Unicode Standard, Version 5.1.0 or later and ISO/IEC 10646. If the adopted ISO/IEC 10646-1 subset is not otherwise specified, it is presumed to be the Unicode set, collection 10646.
A conforming implementation of ECMAScript that provides an application programming interface that supports programs that need to adapt to the linguistic and cultural conventions used by different human languages and countries must implement the interface defined by the most recent edition of ECMA-402 that is compatible with this specification.
A conforming implementation of ECMAScript may provide additional types, values, objects, properties, and functions beyond those described in this specification. In particular, a conforming implementation of ECMAScript may provide properties not described in this specification, and values for those properties, for objects that are described in this specification.
A conforming implementation of ECMAScript may support program and regular expression syntax not described in this specification. In particular, a conforming implementation of ECMAScript may support program syntax that makes use of the “future reserved words” listed in subclause 11.6.2.2 of this specification.
A conforming implementation of ECMAScript must not implement any extension that is listed as a Forbidden Extension in subclause 16.1.
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 10646:2003: Information Technology – Universal Multiple-Octet Coded Character Set (UCS) plus Amendment 1:2005, Amendment 2:2006, Amendment 3:2008, and Amendment 4:2008, plus additional amendments and corrigenda, or successor
ECMA-402, ECMAScript 2015 Internationalization API Specification.
https://www.ecma-international.org/publications-and-standards/standards/ecma-402/
ECMA-404, The JSON Data Interchange Format.
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/
This section contains a non-normative overview of the ECMAScript language.
ECMAScript is an object-oriented programming language for performing computations and manipulating computational objects within a host environment. ECMAScript as defined here is not intended to be computationally self-sufficient; indeed, there are no provisions in this specification for input of external data or output of computed results. Instead, it is expected that the computational environment of an ECMAScript program will provide not only the objects and other facilities described in this specification but also certain environment-specific objects, whose description and behaviour are beyond the scope of this specification except to indicate that they may provide certain properties that can be accessed and certain functions that can be called from an ECMAScript program.
ECMAScript was originally designed to be used as a scripting language, but has become widely used as a general purpose programming language. A scripting language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. In such systems, useful functionality is already available through a user interface, and the scripting language is a mechanism for exposing that functionality to program control. In this way, the existing system is said to provide a host environment of objects and facilities, which completes the capabilities of the scripting language. A scripting language is intended for use by both professional and non-professional programmers.
ECMAScript was originally designed to be a Web scripting language, providing a mechanism to enliven Web pages in browsers and to perform server computation as part of a Web-based client-server architecture. ECMAScript is now used to provide core scripting capabilities for a variety of host environments. Therefore the core language is specified in this document apart from any particular host environment.
ECMAScript usage has moved beyond simple scripting and it is now used for the full spectrum of programming tasks in many different environments and scales. As the usage of ECMAScript has expanded, so has the features and facilities it provides. ECMAScript is now a fully featured general propose programming language.
Some of the facilities of ECMAScript are similar to those used in other programming languages; in particular C, Java™, Self, and Scheme as described in:
ISO/IEC 9899:1996, Programming Languages – C.
Gosling, James, Bill Joy and Guy Steele. The Java™ Language Specification. Addison Wesley Publishing Co., 1996.
Ungar, David, and Smith, Randall B. Self: The Power of Simplicity. OOPSLA '87 Conference Proceedings, pp. 227–241, Orlando, FL, October 1987.
IEEE Standard for the Scheme Programming Language. IEEE Std 1178-1990.
A web browser provides an ECMAScript host environment for client-side computation including, for instance, objects that represent windows, menus, pop-ups, dialog boxes, text areas, anchors, frames, history, cookies, and input/output. Further, the host environment provides a means to attach scripting code to events such as change of focus, page and image loading, unloading, error and abort, selection, form submission, and mouse actions. Scripting code appears within the HTML and the displayed page is a combination of user interface elements and fixed and computed text and images. The scripting code is reactive to user interaction and there is no need for a main program.
A web server provides a different host environment for server-side computation including objects representing requests, clients, and files; and mechanisms to lock and share data. By using browser-side and server-side scripting together, it is possible to distribute computation between the client and server while providing a customized user interface for a Web-based application.
Each Web browser and server that supports ECMAScript supplies its own host environment, completing the ECMAScript execution environment.
The following is an informal overview of ECMAScript—not all parts of the language are described. This overview is not part of the standard proper.
ECMAScript is object-based: basic language and host facilities are provided by objects, and an ECMAScript program is a cluster of communicating objects. In ECMAScript, an object is a collection of zero or more properties each with attributes that determine how each property can be used—for example, when the Writable attribute for a property is set to false, any attempt by executed ECMAScript code to assign a different value to the property fails. Properties are containers that hold other objects, primitive values, or functions. A primitive value is a member of one of the following built-in types: Undefined, Null, Boolean, Number, String, and Symbol; an object is a member of the built-in type Object; and a function is a callable object. A function that is associated with an object via a property is called a method.
ECMAScript defines a collection of built-in objects that round out the definition of ECMAScript entities. These built-in objects include the global object; objects that are fundamental to the runtime semantics of the language including Object, Function, Boolean, Symbol, and various Error objects; objects that represent and manipulate numeric values including Math, Number, and Date; the text processing objects String and RegExp; objects that are indexed collections of values including Array and nine different kinds of Typed Arrays whose elements all have a specific numeric data representation; keyed collections including Map and Set objects; objects supporting structured data including the JSON object, ArrayBuffer, and DataView; objects supporting control abstractions including generator functions and Promise objects; and, reflection objects including Proxy and Reflect.
ECMAScript also defines a set of built-in operators. ECMAScript operators include various unary operations, multiplicative operators, additive operators, bitwise shift operators, relational operators, equality operators, binary bitwise operators, binary logical operators, assignment operators, and the comma operator.
Large ECMAScript programs are supported by modules which allow a program to be divided into multiple sequences of statements and declarations. Each module explicitly identifies declarations it uses that need to be provided by other modules and which of its declarations are available for use by other modules.
ECMAScript syntax intentionally resembles Java syntax. ECMAScript syntax is relaxed to enable it to serve as an easy-to-use scripting language. For example, a variable is not required to have its type declared nor are types associated with properties, and defined functions are not required to have their declarations appear textually before calls to them.
Even though ECMAScript includes syntax for class definitions, ECMAScript objects are not fundamentally class-based such
as those in C++, Smalltalk, or Java. Instead objects may be created in various ways including via a literal notation or via
constructors which create objects and then execute code that initializes all or part of them by assigning
initial values to their properties. Each constructor is a function that has a property named "prototype"
that
is used to implement prototype-based inheritance and shared properties. Objects are created by
using constructors in new expressions; for example, new Date(2009,11)
creates a new Date object.
Invoking a constructor without using new has consequences that depend on the constructor. For example,
Date()
produces a string representation of the current date and time rather than an object.
Every object created by a constructor has an implicit reference (called the object’s prototype) to the value
of its constructor’s "prototype"
property. Furthermore, a prototype may have a non-null implicit
reference to its prototype, and so on; this is called the prototype chain. When a reference is made to a property in
an object, that reference is to the property of that name in the first object in the prototype chain that contains a
property of that name. In other words, first the object mentioned directly is examined for such a property; if that object
contains the named property, that is the property to which the reference refers; if that object does not contain the named
property, the prototype for that object is examined next; and so on.
In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behaviour. In ECMAScript, the state and methods are carried by objects, while structure, behaviour, and state are all inherited.
All objects that do not directly contain a particular property that their prototype contains share that property and its value. Figure 1 illustrates this:
CF is a constructor (and also an object). Five objects have been created by using new
expressions:
cf1, cf2, cf3, cf4, and cf5. Each
of these objects contains properties named q1
and q2
. The dashed lines represent the implicit
prototype relationship; so, for example, cf3’s prototype is CFp. The constructor,
CF, has two properties itself, named P1
and P2
, which are not visible to
CFp, cf1, cf2, cf3, cf4, or
cf5. The property named CFP1
in CFp is shared by cf1,
cf2, cf3, cf4, and cf5 (but not by CF), as
are any properties found in CFp’s implicit prototype chain that are not named q1
,
q2
, or CFP1
. Notice that there is no implicit prototype link between CF and
CFp.
Unlike most class-based object languages, properties can be added to objects dynamically by assigning values to them. That is, constructors are not required to name or assign values to all or any of the constructed object’s properties. In the above diagram, one could add a new shared property for cf1, cf2, cf3, cf4, and cf5 by assigning a new value to the property in CFp.
Although ECMAScript objects are not inherently class-based, it is often convenient to define class-like abstractions based upon a common pattern of constructor functions, prototype objects, and methods. The ECMAScript built-in objects themselves follow such a class-like pattern. Beginning with ECMAScript 2015, the ECMAScript language includes syntactic class definitions that permit programmers to concisely define objects that conform to the same class-like abstraction pattern used by the built-in objects.
The ECMAScript Language recognizes the possibility that some users of the language may wish to restrict their usage of some features available in the language. They might do so in the interests of security, to avoid what they consider to be error-prone features, to get enhanced error checking, or for other reasons of their choosing. In support of this possibility, ECMAScript defines a strict variant of the language. The strict variant of the language excludes some specific syntactic and semantic features of the regular ECMAScript language and modifies the detailed semantics of some features. The strict variant also specifies additional error conditions that must be reported by throwing error exceptions in situations that are not specified as errors by the non-strict form of the language.
The strict variant of ECMAScript is commonly referred to as the strict mode of the language. Strict mode selection and use of the strict mode syntax and semantics of ECMAScript is explicitly made at the level of individual ECMAScript source text units. Because strict mode is selected at the level of a syntactic source text unit, strict mode only imposes restrictions that have local effect within such a source text unit. Strict mode does not restrict or modify any aspect of the ECMAScript semantics that must operate consistently across multiple source text units. A complete ECMAScript program may be composed of both strict mode and non-strict mode ECMAScript source text units. In this case, strict mode only applies when actually executing code that is defined within a strict mode source text unit.
In order to conform to this specification, an ECMAScript implementation must implement both the full unrestricted ECMAScript language and the strict variant of the ECMAScript language as defined by this specification. In addition, an implementation must support the combination of unrestricted and strict mode source text units into a single composite program.
For the purposes of this document, the following terms and definitions apply.
set of data values as defined in clause 6 of this specification
member of one of the types Undefined, Null, Boolean, Number, Symbol, or String as defined in clause 6
NOTE A primitive value is a datum that is represented directly at the lowest level of the language implementation.
member of the type Object
NOTE An object is a collection of properties and has a single prototype object. The prototype may be the null value.
function object that creates and initializes objects
NOTE The value of a constructor’s prototype
property is a prototype object
that is used to implement inheritance and shared properties.
object that provides shared properties for other objects
NOTE When a constructor creates an object, that object implicitly references the
constructor’s prototype
property for the purpose of resolving property references. The
constructor’s prototype
property can be referenced by the program expression
constructor.prototype
, and properties added to an object’s prototype are shared, through
inheritance, by all objects sharing the prototype. Alternatively, a new object may be created with an explicitly specified
prototype by using the Object.create
built-in function.
object that has the default behaviour for the essential internal methods that must be supported by all objects
object that does not have the default behaviour for one or more of the essential internal methods that must be supported by all objects
NOTE Any object that is not an ordinary object is an exotic object.
object whose semantics are defined by this specification
object specified and supplied by an ECMAScript implementation
NOTE Standard built-in objects are defined in this specification. An ECMAScript implementation may specify and supply additional kinds of built-in objects. A built-in constructor is a built-in object that is also a constructor.
primitive value used when a variable has not been assigned a value
type whose sole value is the undefined value
primitive value that represents the intentional absence of any object value
type whose sole value is the null value
member of the Boolean type
NOTE There are only two Boolean values, true and false
type consisting of the primitive values true and false
member of the Object type that is an instance of the standard built-in Boolean
constructor
NOTE A Boolean object is created by using the Boolean
constructor in a
new
expression, supplying a Boolean value as an argument. The resulting object has an internal slot whose value is the Boolean value. A Boolean
object can be coerced to a Boolean value.
primitive value that is a finite ordered sequence of zero or more 16-bit unsigned integer
NOTE A String value is a member of the String type. Each integer value in the sequence usually represents a single 16-bit unit of UTF-16 text. However, ECMAScript does not place any restrictions or requirements on the values except that they must be 16-bit unsigned integers.
set of all possible String values
member of the Object type that is an instance of the standard built-in String
constructor
NOTE A String object is created by using the String
constructor in a
new
expression, supplying a String value as an argument. The resulting object has an internal slot whose value is the String value. A String object
can be coerced to a String value by calling the String
constructor as a function (21.1.1.1).
primitive value corresponding to a double-precision 64-bit binary format IEEE 754-2008 value
NOTE A Number value is a member of the Number type and is a direct representation of a number.
set of all possible Number values including the special “Not-a-Number” (NaN) value, positive infinity, and negative infinity
member of the Object type that is an instance of the standard built-in Number
constructor
NOTE A Number object is created by using the Number
constructor in a
new
expression, supplying a number value as an argument. The resulting object has an internal slot whose value is the number value. A Number object
can be coerced to a number value by calling the Number
constructor as a function (20.1.1.1).
number value that is the positive infinite number value
number value that is an IEEE 754-2008 “Not-a-Number” value
primitive value that represents a unique, non-String Object property key
set of all possible Symbol values
member of the Object type that is an instance of the standard built-in Symbol
constructor
member of the Object type that may be invoked as a subroutine
NOTE In addition to its properties, a function contains executable code and state that determine how it behaves when invoked. A function’s code may or may not be written in ECMAScript.
built-in object that is a function
NOTE Examples of built-in functions include parseInt
and Math.exp
. An implementation may provide implementation-dependent built-in functions that
are not described in this specification.
part of an object that associates a key (either a String value or a Symbol value) and a value
NOTE Depending upon the form of the property the value may be represented either directly as a data value (a primitive value, an object, or a function object) or indirectly by a pair of accessor functions.
function that is the value of a property
NOTE When a function is called as a method of an object, the object is passed to the function as its this value.
method that is a built-in function
NOTE Standard built-in methods are defined in this specification, and an ECMAScript implementation may specify and provide other additional built-in methods.
internal value that defines some characteristic of a property
property that is directly contained by its object
property of an object that is not an own property but is a property (either own or inherited) of the object’s prototype
The remainder of this specification is organized as follows:
Clause 5 defines the notational conventions used throughout the specification.
Clauses 6−9 define the execution environment within which ECMAScript programs operate.
Clauses 10−16 define the actual ECMAScript programming language including its syntactic encoding and the execution semantics of all language features.
Clauses 17−26 define the ECMAScript standard library. It includes the definitions of all of the standard objects that are available for use by ECMAScript programs as they execute.
A context-free grammar consists of a number of productions. Each production has an abstract symbol called a nonterminal as its left-hand side, and a sequence of zero or more nonterminal and terminal symbols as its right-hand side. For each grammar, the terminal symbols are drawn from a specified alphabet.
A chain production is a production that has exactly one nonterminal symbol on its right-hand side along with zero or more terminal symbols.
Starting from a sentence consisting of a single distinguished nonterminal, called the goal symbol, a given context-free grammar specifies a language, namely, the (perhaps infinite) set of possible sequences of terminal symbols that can result from repeatedly replacing any nonterminal in the sequence with a right-hand side of a production for which the nonterminal is the left-hand side.
A lexical grammar for ECMAScript is given in clause 11. This grammar has as its terminal symbols Unicode code points that conform to the rules for SourceCharacter defined in 10.1. It defines a set of productions, starting from the goal symbol InputElementDiv, InputElementTemplateTail, or InputElementRegExp, or InputElementRegExpOrTemplateTail, that describe how sequences of such code points are translated into a sequence of input elements.
Input elements other than white space and comments form the terminal symbols for the syntactic grammar for ECMAScript and
are called ECMAScript tokens. These tokens are the reserved words, identifiers, literals, and punctuators of the
ECMAScript language. Moreover, line terminators, although not considered to be tokens, also become part of the stream of
input elements and guide the process of automatic semicolon insertion (11.9). Simple white space and single-line comments are discarded and do not
appear in the stream of input elements for the syntactic grammar. A MultiLineComment (that is, a
comment of the form /*
…*/
regardless of whether it spans more than one line) is likewise
simply discarded if it contains no line terminator; but if a MultiLineComment contains one or more
line terminators, then it is replaced by a single line terminator, which becomes part of the stream of input elements for
the syntactic grammar.
A RegExp grammar for ECMAScript is given in 21.2.1. This grammar also has as its terminal symbols the code points as defined by SourceCharacter. It defines a set of productions, starting from the goal symbol Pattern, that describe how sequences of code points are translated into regular expression patterns.
Productions of the lexical and RegExp grammars are distinguished by having two colons “::” as separating punctuation. The lexical and RegExp grammars share some productions.
Another grammar is used for translating Strings into numeric values. This grammar is similar to the part of the lexical grammar having to do with numeric literals and has as its terminal symbols SourceCharacter. This grammar appears in 7.1.3.1.
Productions of the numeric string grammar are distinguished by having three colons “:::” as punctuation.
The syntactic grammar for ECMAScript is given in clauses 11, 12, 13, 14, and 15. This grammar has ECMAScript tokens defined by the lexical grammar as its terminal symbols (5.1.2). It defines a set of productions, starting from two alternative goal symbols Script and Module, that describe how sequences of tokens form syntactically correct independent components of ECMAScript programs.
When a stream of code points is to be parsed as an ECMAScript Script or Module, it is first converted to a stream of input elements by repeated application of the lexical grammar; this stream of input elements is then parsed by a single application of the syntactic grammar. The input stream is syntactically in error if the tokens in the stream of input elements cannot be parsed as a single instance of the goal nonterminal (Script or Module), with no tokens left over.
Productions of the syntactic grammar are distinguished by having just one colon “:” as punctuation.
The syntactic grammar as presented in clauses 12, 13, 14 and 15 is not a complete account of which token sequences are accepted as a correct ECMAScript Script or Module. Certain additional token sequences are also accepted, namely, those that would be described by the grammar if only semicolons were added to the sequence in certain places (such as before line terminator characters). Furthermore, certain token sequences that are described by the grammar are not considered acceptable if a line terminator character appears in certain “awkward” places.
In certain cases in order to avoid ambiguities the syntactic grammar uses generalized productions that permit token sequences that do not form a valid ECMAScript Script or Module. For example, this technique is used for object literals and object destructuring patterns. In such cases a more restrictive supplemental grammar is provided that further restricts the acceptable token sequences. In certain contexts, when explicitly specified, the input elements corresponding to such a production are parsed again using a goal symbol of a supplemental grammar. The input stream is syntactically in error if the tokens in the stream of input elements parsed by a cover grammar cannot be parsed as a single instance of the corresponding supplemental goal symbol, with no tokens left over.
Terminal symbols of the lexical, RegExp, and numeric string grammars are shown in fixed width
font, both in
the productions of the grammars and throughout this specification whenever the text directly refers to such a terminal
symbol. These are to appear in a script exactly as written. All terminal symbol code points specified in this way are to be
understood as the appropriate Unicode code points from the Basic Latin range, as opposed to any similar-looking code points
from other Unicode ranges.
Nonterminal symbols are shown in italic type. The definition of a nonterminal (also called a “production”) is introduced by the name of the nonterminal being defined followed by one or more colons. (The number of colons indicates to which grammar the production belongs.) One or more alternative right-hand sides for the nonterminal then follow on succeeding lines. For example, the syntactic definition:
while
(
Expression )
Statementstates that the nonterminal WhileStatement represents the token while
, followed by a
left parenthesis token, followed by an Expression, followed by a right parenthesis token, followed
by a Statement. The occurrences of Expression and Statement are themselves nonterminals. As another example, the syntactic definition:
,
AssignmentExpressionstates that an ArgumentList may represent either a single AssignmentExpression or an ArgumentList, followed by a comma, followed by an AssignmentExpression. This definition of ArgumentList is recursive, that is, it is defined in terms of itself. The result is that an ArgumentList may contain any positive number of arguments, separated by commas, where each argument expression is an AssignmentExpression. Such recursive definitions of nonterminals are common.
The subscripted suffix “opt”, which may appear after a terminal or nonterminal, indicates an optional symbol. The alternative containing the optional symbol actually specifies two right-hand sides, one that omits the optional element and one that includes it. This means that:
is a convenient abbreviation for:
and that:
for
(
LexicalDeclaration Expressionopt ;
Expressionopt )
Statementis a convenient abbreviation for:
for
(
LexicalDeclaration ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expression ;
Expressionopt )
Statementwhich in turn is an abbreviation for:
for
(
LexicalDeclaration ;
)
Statementfor
(
LexicalDeclaration ;
Expression )
Statementfor
(
LexicalDeclaration Expression ;
)
Statementfor
(
LexicalDeclaration Expression ;
Expression )
Statementso, in this example, the nonterminal IterationStatement actually has four alternative right-hand sides.
A production may be parameterized by a subscripted annotation of the form “[parameters]”, which may appear as a suffix to the nonterminal symbol defined by the production. “parameters” may be either a single name or a comma separated list of names. A parameterized production is shorthand for a set of productions defining all combinations of the parameter names, preceded by an underscore, appended to the parameterized nonterminal symbol. This means that:
is a convenient abbreviation for:
and that:
is an abbreviation for:
Multiple parameters produce a combinatory number of productions, not all of which are necessarily referenced in a complete grammar.
References to nonterminals on the right-hand side of a production can also be parameterized. For example:
is equivalent to saying:
A nonterminal reference may have both a parameter list and an “opt” suffix. For example:
is an abbreviation for:
Prefixing a parameter name with “?” on a right-hand side nonterminal reference makes that parameter value dependent upon the occurrence of the parameter name on the reference to the current production’s left-hand side symbol. For example:
is an abbreviation for:
If a right-hand side alternative is prefixed with “[+parameter]” that alternative is only available if the named parameter was used in referencing the production’s nonterminal symbol. If a right-hand side alternative is prefixed with “[~parameter]” that alternative is only available if the named parameter was not used in referencing the production’s nonterminal symbol. This means that:
is an abbreviation for:
and that
is an abbreviation for:
When the words “one of” follow the colon(s) in a grammar definition, they signify that each of the terminal symbols on the following line or lines is an alternative definition. For example, the lexical grammar for ECMAScript contains the production:
1
2
3
4
5
6
7
8
9
which is merely a convenient abbreviation for:
1
2
3
4
5
6
7
8
9
If the phrase “[empty]” appears as the right-hand side of a production, it indicates that the production's right-hand side contains no terminals or nonterminals.
If the phrase “[lookahead ∉ set]” appears in the right-hand side of a production, it indicates that the production may not be used if the immediately following input token sequence is a member of the given set. The set can be written as a comma separated list of one or two element terminal sequences enclosed in curly brackets. For convenience, the set can also be written as a nonterminal, in which case it represents the set of all terminals to which that nonterminal could expand. If the set consists of a single terminal the phrase “[lookahead ≠ terminal]” may be used.
For example, given the definitions
0
1
2
3
4
5
6
7
8
9
the definition
n
[lookahead ∉ {1
, 3
, 5
, 7
, 9
}] DecimalDigitsmatches either the letter n
followed by one or more decimal digits the first of which is even, or a decimal
digit not followed by another decimal digit.
If the phrase “[no LineTerminator here]” appears in the right-hand side of a production of the syntactic grammar, it indicates that the production is a restricted production: it may not be used if a LineTerminator occurs in the input stream at the indicated position. For example, the production:
throw
[no LineTerminator here] Expression ;
indicates that the production may not be used if a LineTerminator occurs in the script between
the throw
token and the Expression.
Unless the presence of a LineTerminator is forbidden by a restricted production, any number of occurrences of LineTerminator may appear between any two consecutive tokens in the stream of input elements without affecting the syntactic acceptability of the script.
When an alternative in a production of the lexical grammar or the numeric string grammar appears to be a multi-code point token, it represents the sequence of code points that would make up such a token.
The right-hand side of a production may specify that certain expansions are not permitted by using the phrase “but not” and then indicating the expansions to be excluded. For example, the production:
means that the nonterminal Identifier may be replaced by any sequence of code points that could replace IdentifierName provided that the same sequence of code points could not replace ReservedWord.
Finally, a few nonterminal symbols are described by a descriptive phrase in sans-serif type in cases where it would be impractical to list all the alternatives:
The specification often uses a numbered list to specify steps in an algorithm. These algorithms are used to precisely specify the required semantics of ECMAScript language constructs. The algorithms are not intended to imply the use of any specific implementation technique. In practice, there may be more efficient algorithms available to implement a given feature.
Algorithms may be explicitly parameterized, in which case the names and usage of the parameters must be provided as part of the algorithm’s definition. In order to facilitate their use in multiple parts of this specification, some algorithms, called abstract operations, are named and written in parameterized functional form so that they may be referenced by name from within other algorithms. Abstract operations are typically referenced using a functional application style such as operationName(arg1, arg2). Some abstract operations are treated as polymorphically dispatched methods of class-like specification abstractions. Such method-like abstract operations are typically referenced using a method application style such as someValue.operationName(arg1, arg2).
Algorithms may be associated with productions of one of the ECMAScript grammars. A production that has multiple alternative definitions will typically have a distinct algorithm for each alternative. When an algorithm is associated with a grammar production, it may reference the terminal and nonterminal symbols of the production alternative as if they were parameters of the algorithm. When used in this manner, nonterminal symbols refer to the actual alternative definition that is matched when parsing the source text.
When an algorithm is associated with a production alternative, the alternative is typically shown without any “[ ]” grammar annotations. Such annotations should only affect the syntactic recognition of the alternative and have no effect on the associated semantics for the alternative.
Unless explicitly specified otherwise, all chain productions have an implicit definition for every algorithm that might be applied to that production’s left-hand side nonterminal. The implicit definition simply reapplies the same algorithm name with the same parameters, if any, to the chain production’s sole right-hand side nonterminal and then returns the result. For example, assume there is a production:
{
StatementList }
but there is no corresponding Evaluation algorithm that is explicitly specified for that production. If in some algorithm there is a statement of the form: “Return the result of evaluating Block” it is implicit that an Evaluation algorithm exists of the form:
Runtime Semantics: Evaluation
{
StatementList }
For clarity of expression, algorithm steps may be subdivided into sequential substeps. Substeps are indented and may themselves be further divided into indented substeps. Outline numbering conventions are used to identify substeps with the first level of substeps labelled with lower case alphabetic characters and the second level of substeps labelled with lower case roman numerals. If more than three levels are required these rules repeat with the fourth level using numeric labels. For example:
A step or substep may be written as an “if” predicate that conditions its substeps. In this case, the substeps are only applied if the predicate is true. If a step or substep begins with the word “else”, it is a predicate that is the negation of the preceding “if” predicate step at the same level.
A step may specify the iterative application of its substeps.
A step that begins with “Assert:” asserts an invariant condition of its algorithm. Such assertions are used to make explicit algorithmic invariants that would otherwise be implicit. Such assertions add no additional semantic requirements and hence need not be checked by an implementation. They are used simply to clarify algorithms.
Mathematical operations such as addition, subtraction, negation, multiplication, division, and the mathematical functions defined later in this clause should always be understood as computing exact mathematical results on mathematical real numbers, which unless otherwise noted do not include infinities and do not include a negative zero that is distinguished from positive zero. Algorithms in this standard that model floating-point arithmetic include explicit steps, where necessary, to handle infinities and signed zero and to perform rounding. If a mathematical operation or function is applied to a floating-point number, it should be understood as being applied to the exact mathematical value represented by that floating-point number; such a floating-point number must be finite, and if it is +0 or −0 then the corresponding mathematical value is simply 0.
The mathematical function abs(x) produces the absolute value of x, which is −x if x is negative (less than zero) and otherwise is x itself.
The mathematical function sign(x) produces 1 if x is positive and −1 if x is negative. The sign function is not used in this standard for cases when x is zero.
The mathematical function min(x1, x2, ..., xn) produces the mathematically smallest of x1 through xn. The mathematical function max(x1, x2, ..., xn) produces the mathematically largest of x1 through xn. The domain and range of these mathematical functions include +∞ and −∞.
The notation “x modulo y” (y must be finite and nonzero) computes a value k of the same sign as y (or zero) such that abs(k) < abs(y) and x−k = q × y for some integer q.
The mathematical function floor(x) produces the largest integer (closest to positive infinity) that is not larger than x.
NOTE floor(x) = x−(x modulo 1).
Context-free grammars are not sufficiently powerful to express all the rules that define whether a stream of input elements form a valid ECMAScript Script or Module that may be evaluated. In some situations additional rules are needed that may be expressed using either ECMAScript algorithm conventions or prose requirements. Such rules are always associated with a production of a grammar and are called the static semantics of the production.
Static Semantic Rules have names and typically are defined using an algorithm. Named Static Semantic Rules are associated with grammar productions and a production that has multiple alternative definitions will typically have for each alternative a distinct algorithm for each applicable named static semantic rule.
Unless otherwise specified every grammar production alternative in this specification implicitly has a definition for a static semantic rule named Contains which takes an argument named symbol whose value is a terminal or nonterminal of the grammar that includes the associated production. The default definition of Contains is:
The above definition is explicitly over-ridden for specific productions.
A special kind of static semantic rule is an Early Error Rule. Early error rules define early error conditions (see clause 16) that are associated with specific grammar productions. Evaluation of most early error rules are not explicitly invoked within the algorithms of this specification. A conforming implementation must, prior to the first evaluation of a Script or Module, validate all of the early error rules of the productions used to parse that Script or Module. If any of the early error rules are violated the Script or Module is invalid and cannot be evaluated.
Algorithms within this specification manipulate values each of which has an associated type. The possible value types are exactly those defined in this clause. Types are further subclassified into ECMAScript language types and specification types.
Within this specification, the notation “Type(x)” is used as shorthand for “the type of x” where “type” refers to the ECMAScript language and specification types defined in this clause. When the term “empty” is used as if it was naming a value, it is equivalent to saying “no value of any type”.
An ECMAScript language type corresponds to values that are directly manipulated by an ECMAScript programmer using the ECMAScript language. The ECMAScript language types are Undefined, Null, Boolean, String, Symbol, Number, and Object. An ECMAScript language value is a value that is characterized by an ECMAScript language type.
The Undefined type has exactly one value, called undefined. Any variable that has not been assigned a value has the value undefined.
The Null type has exactly one value, called null.
The Boolean type represents a logical entity having two values, called true and false.
The String type is the set of all ordered sequences of zero or more 16-bit unsigned integer values (“elements”) up to a maximum length of 253-1 elements. The String type is generally used to represent textual data in a running ECMAScript program, in which case each element in the String is treated as a UTF-16 code unit value. Each element is regarded as occupying a position within the sequence. These positions are indexed with nonnegative integers. The first element (if any) is at index 0, the next element (if any) at index 1, and so on. The length of a String is the number of elements (i.e., 16-bit values) within it. The empty String has length zero and therefore contains no elements.
Where ECMAScript operations interpret String values, each element is interpreted as a single UTF-16 code unit. However,
ECMAScript does not place any restrictions or requirements on the sequence of code units in a String value, so they may be
ill-formed when interpreted as UTF-16 code unit sequences. Operations that do not interpret String contents treat them as
sequences of undifferentiated 16-bit unsigned integers. The function String.prototype.normalize
(see
21.1.3.12) can be used to explicitly normalize a String value. String.prototype.localeCompare
(see 21.1.3.10) internally normalizes String values, but no other operations
implicitly normalize the strings upon which they operate. Only operations that are explicitly specified to be language or
locale sensitive produce language-sensitive results.
NOTE The rationale behind this design was to keep the implementation of Strings as simple and high-performing as possible. If ECMAScript source text is in Normalized Form C, string literals are guaranteed to also be normalized, as long as they do not contain any Unicode escape sequences.
Some operations interpret String contents as UTF-16 encoded Unicode code points. In that case the interpretation is:
A code unit in the range 0 to 0xD7FF or in the range 0xE000 to 0xFFFF is interpreted as a code point with the same value.
A sequence of two code units, where the first code unit c1 is in the range 0xD800 to 0xDBFF and the second code unit c2 is in the range 0xDC00 to 0xDFFF, is a surrogate pair and is interpreted as a code point with the value (c1 - 0xD800) × 0x400 + (c2 – 0xDC00) + 0x10000. (See 10.1.2)
A code unit that is in the range 0xD800 to 0xDFFF, but is not part of a surrogate pair, is interpreted as a code point with the same value.
The Symbol type is the set of all non-String values that may be used as the key of an Object property (6.1.7).
Each possible Symbol value is unique and immutable.
Each Symbol value immutably holds an associated value called [[Description]] that is either undefined or a String value.
Well-known symbols are built-in Symbol values that are explicitly referenced by algorithms of this specification. They are typically used as the keys of properties whose values serve as extension points of a specification algorithm. Unless otherwise specified, well-known symbols values are shared by all Code Realms (8.2).
Within this specification a well-known symbol is referred to by using a notation of the form @@name, where “name” is one of the values listed in Table 1.
Specification Name | [[Description]] | Value and Purpose |
---|---|---|
@@hasInstance | "Symbol.hasInstance" |
A method that determines if a constructor object recognizes an object as one of the constructor’s instances. Called by the semantics of the instanceof operator. |
@@isConcatSpreadable | "Symbol.isConcatSpreadable" |
A Boolean valued property that if true indicates that an object should be flattened to its array elements by Array.prototype.concat . |
@@iterator | "Symbol.iterator" |
A method that returns the default Iterator for an object. Called by the semantics of the for-of statement. |
@@match | "Symbol.match" |
A regular expression method that matches the regular expression against a string. Called by the String.prototype.match method. |
@@replace | "Symbol.replace" |
A regular expression method that replaces matched substrings of a string. Called by the String.prototype.replace method. |
@@search | "Symbol.search" |
A regular expression method that returns the index within a string that matches the regular expression. Called by the String.prototype.search method. |
@@species | "Symbol.species" |
A function valued property that is the constructor function that is used to create derived objects. |
@@split | "Symbol.split" |
A regular expression method that splits a string at the indices that match the regular expression. Called by the String.prototype.split method. |
@@toPrimitive | "Symbol.toPrimitive" |
A method that converts an object to a corresponding primitive value. Called by the ToPrimitive abstract operation. |
@@toStringTag | "Symbol.toStringTag" |
A String valued property that is used in the creation of the default string description of an object. Accessed by the built-in method Object.prototype.toString . |
@@unscopables | "Symbol.unscopables" |
An object valued property whose own property names are property names that are excluded from the with environment bindings of the associated object. |
The Number type has exactly 18437736874454810627 (that is, 264−253+3) values, representing the double-precision
64-bit format IEEE 754-2008 values as specified in the IEEE Standard for Binary Floating-Point Arithmetic, except that the
9007199254740990 (that is, 253−2) distinct “Not-a-Number” values of the IEEE Standard are represented in
ECMAScript as a single special NaN value. (Note that the NaN value is produced by the program expression
NaN
.) In some implementations, external code might be able to detect a difference between various Not-a-Number
values, but such behaviour is implementation-dependent; to ECMAScript code, all NaN values are indistinguishable from each
other.
NOTE The bit pattern that might be observed in an ArrayBuffer (see 24.1) after a Number value has been stored into it is not necessarily the same as the internal representation of that Number value used by the ECMAScript implementation.
There are two other special values, called positive Infinity and negative Infinity. For brevity, these
values are also referred to for expository purposes by the symbols +∞ and −∞, respectively. (Note that these two infinite Number values are produced by the program
expressions +Infinity
(or simply Infinity
) and -Infinity
.)
The other 18437736874454810624 (that is, 264−253) values are called the finite numbers. Half of these are positive numbers and half are negative numbers; for every finite positive Number value there is a corresponding negative value having the same magnitude.
Note that there is both a positive zero and a negative zero. For brevity, these values are also referred to
for expository purposes by the symbols +0 and −0, respectively.
(Note that these two different zero Number values are produced by the program expressions +0
(or simply
0
) and -0
.)
The 18437736874454810622 (that is, 264−253−2) finite nonzero values are of two kinds:
18428729675200069632 (that is, 264−254) of them are normalized, having the form
where s is +1 or −1, m is a positive integer less than 253 but not less than 252, and e is an integer ranging from −1074 to 971, inclusive.
The remaining 9007199254740990 (that is, 253−2) values are denormalized, having the form
where s is +1 or −1, m is a positive integer less than 252, and e is −1074.
Note that all the positive and negative integers whose magnitude is no greater than 253 are representable in the Number type (indeed, the integer 0 has two representations, +0
and -0
).
A finite number has an odd significand if it is nonzero and the integer m used to express it (in one of the two forms shown above) is odd. Otherwise, it has an even significand.
In this specification, the phrase “the Number value for x” where x represents an exact nonzero real mathematical quantity (which might even be an irrational number such as π) means a Number value chosen in the following manner. Consider the set of all finite values of the Number type, with −0 removed and with two additional values added to it that are not representable in the Number type, namely 21024 (which is +1 × 253 × 2971) and −21024 (which is −1 × 253 × 2971). Choose the member of this set that is closest in value to x. If two values of the set are equally close, then the one with an even significand is chosen; for this purpose, the two extra values 21024 and −21024 are considered to have even significands. Finally, if 21024 was chosen, replace it with +∞; if −21024 was chosen, replace it with −∞; if +0 was chosen, replace it with −0 if and only if x is less than zero; any other chosen value is used unchanged. The result is the Number value for x. (This procedure corresponds exactly to the behaviour of the IEEE 754-2008 “round to nearest, ties to even” mode.)
Some ECMAScript operators deal only with integers in specific ranges such as −231 through 231−1, inclusive, or in the range 0 through 216−1, inclusive. These operators accept any value of the Number type but first convert each such value to an integer value in the expected range. See the descriptions of the numeric conversion operations in 7.1.
An Object is logically a collection of properties. Each property is either a data property, or an accessor property:
A data property associates a key value with an ECMAScript language value and a set of Boolean attributes.
An accessor property associates a key value with one or two accessor functions, and a set of Boolean attributes. The accessor functions are used to store or retrieve an ECMAScript language value that is associated with the property.
Properties are identified using key values. A property key value is either an ECMAScript String value or a Symbol value. All String and Symbol values, including the empty string, are valid as property keys. A property name is a property key that is a String value.
An integer index is a String-valued property key that is a canonical numeric String (see 7.1.16) and whose numeric value is either +0 or a positive integer ≤ 253−1. An array index is an integer index whose numeric value i is in the range +0 ≤ i < 232−1.
Property keys are used to access properties and their values. There are two kinds of access for properties: get and set, corresponding to value retrieval and assignment, respectively. The properties accessible via get and set access includes both own properties that are a direct part of an object and inherited properties which are provided by another associated object via a property inheritance relationship. Inherited properties may be either own or inherited properties of the associated object. Each own property of an object must each have a key value that is distinct from the key values of the other own properties of that object.
All objects are logically collections of properties, but there are multiple forms of objects that differ in their semantics for accessing and manipulating their properties. Ordinary objects are the most common form of objects and have the default object semantics. An exotic object is any form of object whose property semantics differ in any way from the default semantics.
Attributes are used in this specification to define and explain the state of Object properties. A data property associates a key value with the attributes listed in Table 2.
Attribute Name | Value Domain | Description |
---|---|---|
[[Value]] | Any ECMAScript language type | The value retrieved by a get access of the property. |
[[Writable]] | Boolean | If false, attempts by ECMAScript code to change the property’s [[Value]] attribute using [[Set]] will not succeed. |
[[Enumerable]] | Boolean | If true, the property will be enumerated by a for-in enumeration (see 13.7.5). Otherwise, the property is said to be non-enumerable. |
[[Configurable]] | Boolean | If false, attempts to delete the property, change the property to be an accessor property, or change its attributes (other than [[Value]], or changing [[Writable]] to false) will fail. |
An accessor property associates a key value with the attributes listed in Table 3.
Attribute Name | Value Domain | Description |
---|---|---|
[[Get]] | Object | Undefined | If the value is an Object it must be a function object. The function’s [[Call]] internal method (Table 6) is called with an empty arguments list to retrieve the property value each time a get access of the property is performed. |
[[Set]] | Object | Undefined | If the value is an Object it must be a function object. The function’s [[Call]] internal method (Table 6) is called with an arguments list containing the assigned value as its sole argument each time a set access of the property is performed. The effect of a property's [[Set]] internal method may, but is not required to, have an effect on the value returned by subsequent calls to the property's [[Get]] internal method. |
[[Enumerable]] | Boolean | If true, the property is to be enumerated by a for-in enumeration (see 13.7.5). Otherwise, the property is said to be non-enumerable. |
[[Configurable]] | Boolean | If false, attempts to delete the property, change the property to be a data property, or change its attributes will fail. |
If the initial values of a property’s attributes are not explicitly specified by this specification, the default value defined in Table 4 is used.
Attribute Name | Default Value |
---|---|
[[Value]] | undefined |
[[Get]] | undefined |
[[Set]] | undefined |
[[Writable]] | false |
[[Enumerable]] | false |
[[Configurable]] | false |
The actual semantics of objects, in ECMAScript, are specified via algorithms called internal methods. Each object in an ECMAScript engine is associated with a set of internal methods that defines its runtime behaviour. These internal methods are not part of the ECMAScript language. They are defined by this specification purely for expository purposes. However, each object within an implementation of ECMAScript must behave as specified by the internal methods associated with it. The exact manner in which this is accomplished is determined by the implementation.
Internal method names are polymorphic. This means that different object values may perform different algorithms when a common internal method name is invoked upon them. That actual object upon which an internal method is invoked is the “target” of the invocation. If, at runtime, the implementation of an algorithm attempts to use an internal method of an object that the object does not support, a TypeError exception is thrown.
Internal slots correspond to internal state that is associated with objects and used by various ECMAScript specification algorithms. Internal slots are not object properties and they are not inherited. Depending upon the specific internal slot specification, such state may consist of values of any ECMAScript language type or of specific ECMAScript specification type values. Unless explicitly specified otherwise, internal slots are allocated as part of the process of creating an object and may not be dynamically added to an object. Unless specified otherwise, the initial value of an internal slot is the value undefined. Various algorithms within this specification create objects that have internal slots. However, the ECMAScript language provides no direct way to associate internal slots with an object.
Internal methods and internal slots are identified within this specification using names enclosed in double square brackets [[ ]].
Table 5 summarizes the essential internal methods used by this specification that are applicable to all objects created or manipulated by ECMAScript code. Every object must have algorithms for all of the essential internal methods. However, all objects do not necessarily use the same algorithms for those methods.
The “Signature” column of Table 5 and other similar tables describes the invocation pattern for each internal method. The invocation pattern always includes a parenthesized list of descriptive parameter names. If a parameter name is the same as an ECMAScript type name then the name describes the required type of the parameter value. If an internal method explicitly returns a value, its parameter list is followed by the symbol “→” and the type name of the returned value. The type names used in signatures refer to the types defined in clause 6 augmented by the following additional names. “any” means the value may be any ECMAScript language type. An internal method implicitly returns a Completion Record as described in 6.2.2. In addition to its parameters, an internal method always has access to the object that is the target of the method invocation.
Internal Method | Signature | Description |
---|---|---|
[[GetPrototypeOf]] | () → Object | Null | Determine the object that provides inherited properties for this object. A null value indicates that there are no inherited properties. |
[[SetPrototypeOf]] | (Object | Null) → Boolean | Associate this object with another object that provides inherited properties. Passing null indicates that there are no inherited properties. Returns true indicating that the operation was completed successfully or false indicating that the operation was not successful. |
[[IsExtensible]] | ( ) → Boolean | Determine whether it is permitted to add additional properties to this object. |
[[PreventExtensions]] | ( ) → Boolean | Control whether new properties may be added to this object. Returns true if the operation was successful or false if the operation was unsuccessful. |
[[GetOwnProperty]] | (propertyKey) → Undefined | Property Descriptor | Return a Property Descriptor for the own property of this object whose key is propertyKey, or undefined if no such property exists. |
[[HasProperty]] | (propertyKey) → Boolean | Return a Boolean value indicating whether this object already has either an own or inherited property whose key is propertyKey. |
[[Get]] | (propertyKey, Receiver) → any |
Return the value of the property whose key is propertyKey from this object. If any ECMAScript code must be executed to retrieve the property value, Receiver is used as the this value when evaluating the code. |
[[Set]] | (propertyKey,value, Receiver) → Boolean |
Set the value of the property whose key is propertyKey to value. If any ECMAScript code must be executed to set the property value, Receiver is used as the this value when evaluating the code. Returns true if the property value was set or false if it could not be set. |
[[Delete]] | (propertyKey) → Boolean | Remove the own property whose key is propertyKey from this object . Return false if the property was not deleted and is still present. Return true if the property was deleted or is not present. |
[[DefineOwnProperty]] | (propertyKey, PropertyDescriptor) → Boolean |
Create or alter the own property, whose key is propertyKey, to have the state described by PropertyDescriptor. Return true if that property was successfully created/updated or false if the property could not be created or updated. |
[[Enumerate]] | ()→Object | Return an iterator object that produces the keys of the string-keyed enumerable properties of the object. |
[[OwnPropertyKeys]] | ()→List of propertyKey | Return a List whose elements are all of the own property keys for the object. |
Table 6 summarizes additional essential internal methods that are supported by objects that may be called as functions. A function object is an object that supports the [[Call]] internal methods. A constructor (also referred to as a constructor function) is a function object that supports the [[Construct]] internal method.
Internal Method | Signature | Description |
---|---|---|
[[Call]] | (any, a List of any) → any |
Executes code associated with this object. Invoked via a function call expression. The arguments to the internal method are a this value and a list containing the arguments passed to the function by a call expression. Objects that implement this internal method are callable. |
[[Construct]] | (a List of any, Object) → Object |
Creates an object. Invoked via the new or super operators. The first argument to the internal method is a list containing the arguments of the operator. The second argument is the object to which the new operator was initially applied. Objects that implement this internal method are called constructors. A function object is not necessarily a constructor and such non-constructor function objects do not have a [[Construct]] internal method. |
The semantics of the essential internal methods for ordinary objects and standard exotic objects are specified in clause 9. If any specified use of an internal method of an exotic object is not supported by an implementation, that usage must throw a TypeError exception when attempted.
The Internal Methods of Objects of an ECMAScript engine must conform to the list of invariants specified below. Ordinary ECMAScript Objects as well as all standard exotic objects in this specification maintain these invariants. ECMAScript Proxy objects maintain these invariants by means of runtime checks on the result of traps invoked on the [[ProxyHandler]] object.
Any implementation provided exotic objects must also maintain these invariants for those objects. Violation of these invariants may cause ECMAScript code to have unpredictable behaviour and create security issues. However, violation of these invariants must never compromise the memory safety of an implementation.
An implementation must not allow these invariants to be circumvented in any manner such as by providing alternative interfaces that implement the functionality of the essential internal methods without enforcing their invariants.
Definitions:
● The target of an internal method is the object upon which the internal method is called.
● A target is non-extensible if it has been observed to return false from its [[IsExtensible]] internal method, or true from its [[PreventExtensions]] internal method.
● A non-existent property is a property that does not exist as an own property on a non-extensible target.
● All references to SameValue are according to the definition of SameValue algorithm specified in 7.2.9.
[[GetPrototypeOf]] ( )
● The Type of the return value must be either Object or Null.
● If target is non-extensible, and [[GetPrototypeOf]] returns a value v, then any future calls to [[GetPrototypeOf]] should return the SameValue as v.
NOTE 1 An object’s prototype chain should have finite length (that is, starting from any object, recursively applying the [[GetPrototypeOf]] internal method to its result should eventually lead to the value null). However, this requirement is not enforceable as an object level invariant if the prototype chain includes any exotic objects that do not use the ordinary object definition of [[GetPrototypeOf]]. Such a circular prototype chain may result in infinite loops when accessing object properties.
[[SetPrototypeOf]] (V)
● The Type of the return value must be Boolean.
● If target is non-extensible, [[SetPrototypeOf]] must return false, unless V is the SameValue as the target’s observed [[GetPrototypeOf]] value.
[[PreventExtensions]] ( )
● The Type of the return value must be Boolean.
● If [[PreventExtensions]] returns true, all future calls to [[IsExtensible]] on the target must return false and the target is now considered non-extensible.
[[GetOwnProperty]] (P)
● The Type of the return value must be either Property Descriptor or Undefined.
● If the Type of the return value is Property Descriptor, the return value must be a complete property descriptor (see 6.2.4.6).
● If a property P is described as a data property with Desc.[[Value]] equal to v and Desc.[[Writable]] and Desc.[[Configurable]] are both false, then the SameValue must be returned for the Desc.[[Value]] attribute of the property on all future calls to [[GetOwnProperty]] ( P ).
● If P’s attributes other than [[Writable]] may change over time or if the property might disappear, then P’s [[Configurable]] attribute must be true.
● If the [[Writable]] attribute may change from false to true, then the [[Configurable]] attribute must be true.
● If the target is non-extensible and P is non-existent, then all future calls to [[GetOwnProperty]] (P) on the target must describe P as non-existent (i.e. [[GetOwnProperty]] (P) must return undefined).
NOTE 2 As a consequence of the third invariant, if a property is described as a data property and it may return different values over time, then either or both of the Desc.[[Writable]] and Desc.[[Configurable]] attributes must be true even if no mechanism to change the value is exposed via the other internal methods.
[[DefineOwnProperty]] (P, Desc)
● The Type of the return value must be Boolean.
● [[DefineOwnProperty]] must return false if P has previously been observed as a non-configurable own property of the target, unless either:
1. P is a non-configurable writable own data property. A non-configurable writable data property can be changed into a non-configurable non-writable data property.
2. All attributes in Desc are the SameValue as P’s attributes.
● [[DefineOwnProperty]] (P, Desc) must return false if target is non-extensible and P is a non-existent own property. That is, a non-extensible target object cannot be extended with new properties.
[[HasProperty]] ( P )
● The Type of the return value must be Boolean.
● If P was previously observed as a non-configurable data or accessor own property of the target, [[HasProperty]] must return true.
[[Get]] (P, Receiver)
● If P was previously observed as a non-configurable, non-writable own data property of the target with value v, then [[Get]] must return the SameValue.
● If P was previously observed as a non-configurable own accessor property of the target whose [[Get]] attribute is undefined, the [[Get]] operation must return undefined.
[[Set]] ( P, V, Receiver)
● The Type of the return value must be Boolean.
● If P was previously observed as a non-configurable, non-writable own data property of the target, then [[Set]] must return false unless V is the SameValue as P’s [[Value]] attribute.
● If P was previously observed as a non-configurable own accessor property of the target whose [[Set]] attribute is undefined, the [[Set]] operation must return false.
[[Delete]] ( P )
● The Type of the return value must be Boolean.
● If P was previously observed to be a non-configurable own data or accessor property of the target, [[Delete]] must return false.
[[Enumerate]] ( )
● The Type of the return value must be Object.
[[OwnPropertyKeys]] ( )
● The return value must be a List.
● The Type of each element of the returned List is either String or Symbol.
● The returned List must contain at least the keys of all non-configurable own properties that have previously been observed.
● If the object is non-extensible, the returned List must contain only the keys of all own properties of the object that are observable using [[GetOwnProperty]].
[[Construct]] ( )
● The Type of the return value must be Object.
Well-known intrinsics are built-in objects that are explicitly referenced by the algorithms of this specification and which usually have Realm specific identities. Unless otherwise specified each intrinsic object actually corresponds to a set of similar objects, one per Realm.
Within this specification a reference such as %name% means the intrinsic object, associated with the current Realm, corresponding to the name. Determination of the current Realm and its intrinsics is described in 8.3. The well-known intrinsics are listed in Table 7.
Intrinsic Name | Global Name | ECMAScript Language Association |
---|---|---|
%Array% | Array |
The Array constructor (22.1.1) |
%ArrayBuffer% | ArrayBuffer |
The ArrayBuffer constructor (24.1.2) |
%ArrayBufferPrototype% | ArrayBuffer.prototype |
The initial value of the prototype data property of %ArrayBuffer%. |
%ArrayIteratorPrototype% | The prototype of Array iterator objects (22.1.5) | |
%ArrayPrototype% | Array.prototype |
The initial value of the prototype data property of %Array% (22.1.3) |
%ArrayProto_values% | Array.prototype.values |
The initial value of the values data property of %ArrayPrototype% (22.1.3.29) |
%Boolean% | Boolean |
The Boolean constructor (19.3.1) |
%BooleanPrototype% | Boolean.prototype |
The initial value of the prototype data property of %Boolean% (19.3.3) |
%DataView% | DataView |
The DataView constructor (24.2.2) |
%DataViewPrototype% | DataView.prototype |
The initial value of the prototype data property of %DataView% |
%Date% | Date |
The Date constructor (20.3.2) |
%DatePrototype% | Date.prototype |
The initial value of the prototype data property of %Date%. |
%decodeURI% | decodeURI |
The decodeURI function (18.2.6.2) |
%decodeURIComponent% | decodeURIComponent |
The decodeURIComponent function (18.2.6.3) |
%encodeURI% | encodeURI |
The encodeURI function (18.2.6.4) |
%encodeURIComponent% | encodeURIComponent |
The encodeURIComponent function (18.2.6.5) |
%Error% | Error |
The Error constructor (19.5.1) |
%ErrorPrototype% | Error.prototype |
The initial value of the prototype data property of %Error% |
%eval% | eval |
The eval function (18.2.1) |
%EvalError% | EvalError |
The EvalError constructor (19.5.5.1) |
%EvalErrorPrototype% | EvalError.prototype |
The initial value of the prototype property of %EvalError% |
%Float32Array% | Float32Array |
The Float32Array constructor (22.2) |
%Float32ArrayPrototype% | Float32Array.prototype |
The initial value of the prototype data property of %Float32Array%. |
%Float64Array% | Float64Array |
The Float64Array constructor (22.2) |
%Float64ArrayPrototype% | Float64Array.prototype |
The initial value of the prototype data property of %Float64Array% |
%Function% | Function |
The Function constructor (19.2.1) |
%FunctionPrototype% | Function.prototype |
The initial value of the prototype data property of %Function% |
%Generator% | The initial value of the prototype property of %GeneratorFunction% |
|
%GeneratorFunction% | The constructor of generator objects (25.2.1) | |
%GeneratorPrototype% | The initial value of the prototype property of %Generator% |
|
%Int8Array% | Int8Array |
The Int8Array constructor (22.2) |
%Int8ArrayPrototype% | Int8Array.prototype |
The initial value of the prototype data property of %Int8Array% |
%Int16Array% | Int16Array |
The Int16Array constructor (22.2) |
%Int16ArrayPrototype% | Int16Array.prototype |
The initial value of the prototype data property of %Int16Array% |
%Int32Array% | Int32Array |
The Int32Array constructor (22.2) |
%Int32ArrayPrototype% | Int32Array.prototype |
The initial value of the prototype data property of %Int32Array% |
%isFinite% | isFinite |
The isFinite function (18.2.2) |
%isNaN% | isNaN |
The isNaN function (18.2.3) |
%IteratorPrototype% | An object that all standard built-in iterator objects indirectly inherit from | |
%JSON% | JSON |
The JSON object (24.3) |
%Map% | Map |
The Map constructor (23.1.1) |
%MapIteratorPrototype% | The prototype of Map iterator objects (23.1.5) | |
%MapPrototype% | Map.prototype |
The initial value of the prototype data property of %Map% |
%Math% | Math |
The Math object (20.2) |
%Number% | Number |
The Number constructor (20.1.1) |
%NumberPrototype% | Number.prototype |
The initial value of the prototype property of %Number% |
%Object% | Object |
The Object constructor (19.1.1) |
%ObjectPrototype% | Object.prototype |
The initial value of the prototype data property of %Object%. (19.1.3) |
%ObjProto_toString% | Object.prototype. |
The initial value of the toString data property of %ObjectPrototype% (19.1.3.6) |
%parseFloat% | parseFloat |
The parseFloat function (18.2.4) |
%parseInt% | parseInt |
The parseInt function (18.2.5) |
%Promise% | Promise |
The Promise constructor (25.4.3) |
%PromisePrototype% | Promise.prototype |
The initial value of the prototype data property of %Promise% |
%Proxy% | Proxy |
The Proxy constructor (26.2.1) |
%RangeError% | RangeError |
The RangeError constructor (19.5.5.2) |
%RangeErrorPrototype% | RangeError.prototype |
The initial value of the prototype property of %RangeError% |
%ReferenceError% | ReferenceError |
The ReferenceError constructor (19.5.5.3) |
%ReferenceErrorPrototype% | ReferenceError. |
The initial value of the prototype property of %ReferenceError% |
%Reflect% | Reflect |
The Reflect object (26.1) |
%RegExp% | RegExp |
The RegExp constructor (21.2.3) |
%RegExpPrototype% | RegExp.prototype |
The initial value of the prototype data property of %RegExp% |
%Set% | Set |
The Set constructor (23.2.1) |
%SetIteratorPrototype% | The prototype of Set iterator objects (23.2.5) | |
%SetPrototype% | Set.prototype |
The initial value of the prototype data property of %Set% |
%String% | String |
The String constructor (21.1.1) |
%StringIteratorPrototype% | The prototype of String iterator objects (21.1.5) | |
%StringPrototype% | String.prototype |
The initial value of the prototype data property of %String% |
%Symbol% | Symbol |
The Symbol constructor (19.4.1) |
%SymbolPrototype% | Symbol.prototype |
The initial value of the prototype data property of %Symbol%. (19.4.3) |
%SyntaxError% | SyntaxError |
The SyntaxError constructor (19.5.5.4) |
%SyntaxErrorPrototype% | SyntaxError.prototype |
The initial value of the prototype property of %SyntaxError% |
%ThrowTypeError% | A function object that unconditionally throws a new instance of %TypeError% | |
%TypedArray% | The super class of all typed Array constructors (22.2.1) | |
%TypedArrayPrototype% | The initial value of the prototype property of %TypedArray% |
|
%TypeError% | TypeError |
The TypeError constructor (19.5.5.5) |
%TypeErrorPrototype% | TypeError.prototype |
The initial value of the prototype property of %TypeError% |
%Uint8Array% | Uint8Array |
The Uint8Array constructor (22.2) |
%Uint8ArrayPrototype% | Uint8Array.prototype |
The initial value of the prototype data property of %Uint8Array% |
%Uint8ClampedArray% | Uint8ClampedArray |
The Uint8ClampedArray constructor (22.2) |
%Uint8ClampedArrayPrototype% | Uint8ClampedArray. |
The initial value of the prototype data property of %Uint8ClampedArray% |
%Uint16Array% | Uint16Array |
The Uint16Array constructor (22.2) |
%Uint16ArrayPrototype% | Uint16Array.prototype |
The initial value of the prototype data property of %Uint16Array% |
%Uint32Array% | Uint32Array |
The Uint32Array constructor (22.2) |
%Uint32ArrayPrototype% | Uint32Array.prototype |
The initial value of the prototype data property of %Uint32Array% |
%URIError% | URIError |
The URIError constructor (19.5.5.6) |
%URIErrorPrototype% | URIError.prototype |
The initial value of the prototype property of %URIError% |
%WeakMap% | WeakMap |
The WeakMap constructor (23.3.1) |
%WeakMapPrototype% | WeakMap.prototype |
The initial value of the prototype data property of %WeakMap% |
%WeakSet% | WeakSet |
The WeakSet constructor (23.4.1) |
%WeakSetPrototype% | WeakSet.prototype |
The initial value of the prototype data property of %WeakSet% |
A specification type corresponds to meta-values that are used within algorithms to describe the semantics of ECMAScript language constructs and ECMAScript language types. The specification types are Reference, List, Completion, Property Descriptor, Lexical Environment, Environment Record, and Data Block. Specification type values are specification artefacts that do not necessarily correspond to any specific entity within an ECMAScript implementation. Specification type values may be used to describe intermediate results of ECMAScript expression evaluation but such values cannot be stored as properties of objects or values of ECMAScript language variables.
The List type is used to explain the evaluation of argument lists (see 12.3.6) in
new
expressions, in function calls, and in other algorithms where a simple ordered list of values is needed.
Values of the List type are simply ordered sequences of list elements containing the individual values. These sequences may
be of any length. The elements of a list may be randomly accessed using 0-origin indices. For notational convenience an
array-like syntax can be used to access List elements. For example, arguments[2] is shorthand for saying the
3rd element of the List arguments.
For notational convenience within this specification, a literal syntax can be used to express a new List value. For example, «1, 2» defines a List value that has two elements each of which is initialized to a specific value. A new empty List can be expressed as «».
The Record type is used to describe data aggregations within the algorithms of this specification. A Record type value consists of one or more named fields. The value of each field is either an ECMAScript value or an abstract value represented by a name associated with the Record type. Field names are always enclosed in double brackets, for example [[value]].
For notational convenience within this specification, an object literal-like syntax can be used to express a Record value. For example, {[[field1]]: 42, [[field2]]: false, [[field3]]: empty} defines a Record value that has three fields, each of which is initialized to a specific value. Field name order is not significant. Any fields that are not explicitly listed are considered to be absent.
In specification text and algorithms, dot notation may be used to refer to a specific field of a Record value. For example, if R is the record shown in the previous paragraph then R.[[field2]] is shorthand for “the field of R named [[field2]]”.
Schema for commonly used Record field combinations may be named, and that name may be used as a prefix to a literal Record value to identify the specific kind of aggregations that is being described. For example: PropertyDescriptor{[[Value]]: 42, [[Writable]]: false, [[Configurable]]: true}.
The Completion type is a Record used to explain the runtime propagation of values and control flow such as the
behaviour of statements (break
, continue
, return
and throw
) that
perform nonlocal transfers of control.
Values of the Completion type are Record values whose fields are defined as by Table 8.
Field | Value | Meaning |
---|---|---|
[[type]] | One of normal, break, continue, return, or throw | The type of completion that occurred. |
[[value]] | any ECMAScript language value or empty | The value that was produced. |
[[target]] | any ECMAScript string or empty | The target label for directed control transfers. |
The term “abrupt completion” refers to any completion with a [[type]] value other than normal.
The abstract operation NormalCompletion with a single argument, such as:
Is a shorthand that is defined as follows:
The algorithms of this specification often implicitly return Completion Records whose [[type]] is normal. Unless it is otherwise obvious from the context, an algorithm statement that returns a value that is not a Completion Record, such as:
"Infinity"
.means the same thing as:
"Infinity"
).However, if the value expression of a “return” statement is a Completion Record construction literal, the resulting Completion Record is returned. If the value expression is a call to an abstract operation, the “return” statement simply returns the Completion Record produced by the abstract operation.
The abstract operation Completion(completionRecord) is used to emphasize that a previously computed Completion Record is being returned. The Completion abstract operation takes a single argument, completionRecord, and performs the following steps:
A “return” statement without a value in an algorithm step means the same thing as:
Any reference to a Completion Record value that is in a context that does not explicitly require a complete Completion Record value is equivalent to an explicit reference to the [[value]] field of the Completion Record value unless the Completion Record is an abrupt completion.
Algorithms steps that say to throw an exception, such as
mean the same things as:
Algorithms steps that say
mean the same thing as:
The abstract operation UpdateEmpty with arguments completionRecord and value performs the following steps:
NOTE The Reference type is used to explain the behaviour of such operators as
delete
, typeof
, the assignment operators, the super
keyword and other language
features. For example, the left-hand operand of an assignment is expected to produce a reference.
A Reference is a resolved name or property binding. A Reference consists of three components, the base value, the referenced name and the Boolean valued strict reference flag. The base value is either undefined, an Object, a Boolean, a String, a Symbol, a Number, or an Environment Record (8.1.1). A base value of undefined indicates that the Reference could not be resolved to a binding. The referenced name is a String or Symbol value.
A Super Reference is a Reference that is used to represents a name binding that was expressed using the super keyword. A Super Reference has an additional thisValue component and its base value will never be an Environment Record.
The following abstract operations are used in this specification to access the components of references:
GetBase(V). Returns the base value component of the reference V.
GetReferencedName(V). Returns the referenced name component of the reference V.
IsStrictReference(V). Returns the strict reference flag component of the reference V.
HasPrimitiveBase(V). Returns true if Type(base) is Boolean, String, Symbol, or Number.
IsPropertyReference(V). Returns true if either the base value is an object or HasPrimitiveBase(V) is true; otherwise returns false.
IsUnresolvableReference(V). Returns true if the base value is undefined and false otherwise.
IsSuperReference(V). Returns true if this reference has a thisValue component.
The following abstract operations are used in this specification to operate on references:
NOTE The object that may be created in step 5.a.ii is not accessible outside of the above abstract operation and the ordinary object [[Get]] internal method. An implementation might choose to avoid the actual creation of the object.
NOTE The object that may be created in step 6.a.ii is not accessible outside of the above algorithm and the ordinary object [[Set]] internal method. An implementation might choose to avoid the actual creation of that object.
The Property Descriptor type is used to explain the manipulation and reification of Object property attributes. Values of the Property Descriptor type are Records. Each field’s name is an attribute name and its value is a corresponding attribute value as specified in 6.1.7.1. In addition, any field may be present or absent. The schema name used within this specification to tag literal descriptions of Property Descriptor records is “PropertyDescriptor”.
Property Descriptor values may be further classified as data Property Descriptors and accessor Property Descriptors based upon the existence or use of certain fields. A data Property Descriptor is one that includes any fields named either [[Value]] or [[Writable]]. An accessor Property Descriptor is one that includes any fields named either [[Get]] or [[Set]]. Any Property Descriptor may have fields named [[Enumerable]] and [[Configurable]]. A Property Descriptor value may not be both a data Property Descriptor and an accessor Property Descriptor; however, it may be neither. A generic Property Descriptor is a Property Descriptor value that is neither a data Property Descriptor nor an accessor Property Descriptor. A fully populated Property Descriptor is one that is either an accessor Property Descriptor or a data Property Descriptor and that has all of the fields that correspond to the property attributes defined in either Table 2 or Table 3.
The following abstract operations are used in this specification to operate upon Property Descriptor values:
When the abstract operation IsAccessorDescriptor is called with Property Descriptor Desc, the following steps are taken:
When the abstract operation IsDataDescriptor is called with Property Descriptor Desc, the following steps are taken:
When the abstract operation IsGenericDescriptor is called with Property Descriptor Desc, the following steps are taken:
When the abstract operation FromPropertyDescriptor is called with Property Descriptor Desc, the following steps are taken:
"value"
,
Desc.[[Value]])."writable"
,
Desc.[[Writable]])."get"
,
Desc.[[Get]])."set"
,
Desc.[[Set]])"enumerable"
,
Desc.[[Enumerable]])."configurable"
,
Desc.[[Configurable]]).When the abstract operation ToPropertyDescriptor is called with object Obj, the following steps are taken:
"enumerable"
)."enumerable"
))."configurable"
)."configurable"
))."value"
)."value"
)."writable"
)."writable"
))."get"
)."get"
)."set"
)."set"
).When the abstract operation CompletePropertyDescriptor is called with Property Descriptor Desc the following steps are taken:
The Lexical Environment and Environment Record types are used to explain the behaviour of name resolution in nested functions and blocks. These types and the operations upon them are defined in 8.1.
The Data Block specification type is used to describe a distinct and mutable sequence of byte-sized (8 bit) numeric values. A Data Block value is created with a fixed number of bytes that each have the initial value 0.
For notational convenience within this specification, an array-like syntax can be used to access the individual bytes of a Data Block value. This notation presents a Data Block value as a 0-origined integer indexed sequence of bytes. For example, if db is a 5 byte Data Block value then db[2] can be used to access its 3rd byte.
The following abstract operations are used in this specification to operate upon Data Block values:
When the abstract operation CreateByteDataBlock is called with integer argument size, the following steps are taken:
When the abstract operation CopyDataBlockBytes is called the following steps are taken:
These operations are not a part of the ECMAScript language; they are defined here to solely to aid the specification of the semantics of the ECMAScript language. Other, more specialized abstract operations are defined throughout this specification.
The ECMAScript language implicitly performs automatic type conversion as needed. To clarify the semantics of certain constructs it is useful to define a set of conversion abstract operations. The conversion abstract operations are polymorphic; they can accept a value of any ECMAScript language type or of a Completion Record value. But no other specification types are used with these operations.
The abstract operation ToPrimitive takes an input argument and an optional argument PreferredType. The abstract operation ToPrimitive converts its input argument to a non-Object type. If an object is capable of converting to more than one primitive type, it may use the optional hint PreferredType to favour that type. Conversion occurs according to Table 9:
Input Type | Result |
---|---|
Completion Record | If input is an abrupt completion, return input. Otherwise return ToPrimitive(input.[[value]]) also passing the optional hint PreferredType. |
Undefined | Return input. |
Null | Return input. |
Boolean | Return input. |
Number | Return input. |
String | Return input. |
Symbol | Return input. |
Object | Perform the steps following this table. |
When Type(input) is Object, the following steps are taken:
"default"
."string"
."number"
."default"
, let hint be "number"
.When the abstract operation OrdinaryToPrimitive is called with arguments O and hint, the following steps are taken:
"string"
or "number"
."string"
, then
"toString"
, "valueOf"
»."valueOf"
, "toString"
».NOTE When ToPrimitive is called with no hint, then it generally behaves as if the hint were Number. However, objects may over-ride this behaviour by defining a @@toPrimitive method. Of the objects defined in this specification only Date objects (see 20.3.4.45) and Symbol objects (see 19.4.3.4) over-ride the default ToPrimitive behaviour. Date objects treat no hint as if the hint were String.
The abstract operation ToBoolean converts argument to a value of type Boolean according to Table 10:
Argument Type | Result |
---|---|
Completion Record | If argument is an abrupt completion, return argument. Otherwise return ToBoolean(argument.[[value]]). |
Undefined | Return false. |
Null | Return false. |
Boolean | Return argument. |
Number | Return false if argument is +0, −0, or NaN; otherwise return true. |
String | Return false if argument is the empty String (its length is zero); otherwise return true. |
Symbol | Return true. |
Object | Return true. |
The abstract operation ToNumber converts argument to a value of type Number according to Table 11:
Argument Type | Result |
---|---|
Completion Record | If argument is an abrupt completion, return argument. Otherwise return ToNumber(argument.[[value]]). |
Undefined | Return NaN. |
Null | Return +0. |
Boolean | Return 1 if argument is true. Return +0 if argument is false. |
Number | Return argument (no conversion). |
String | See grammar and conversion algorithm below. |
Symbol | Throw a TypeError exception. |
Object |
Apply the following steps:
|
ToNumber applied to Strings applies the following grammar to the input String interpreted as a sequence of UTF-16 encoded code points (6.1.4). If the grammar cannot interpret the String as an expansion of StringNumericLiteral, then the result of ToNumber is NaN.
NOTE 1 The terminal symbols of this grammar are all composed of Unicode BMP code points so the result will be NaN if the string contains the UTF-16 encoding of any supplementary code points or any unpaired surrogate code points.
+
StrUnsignedDecimalLiteral-
StrUnsignedDecimalLiteral.
DecimalDigitsopt ExponentPartopt.
DecimalDigits ExponentPartopt0
1
2
3
4
5
6
7
8
9
e
E
+
DecimalDigits-
DecimalDigitsAll grammar symbols not explicitly defined above have the definitions used in the Lexical Grammar for numeric literals (11.8.3)
NOTE 2 Some differences should be noted between the syntax of a StringNumericLiteral and a NumericLiteral (see 11.8.3):
A StringNumericLiteral may include leading and/or trailing white space and/or line terminators.
A StringNumericLiteral that is decimal may have any number of leading 0
digits.
A StringNumericLiteral that is decimal may include a +
or -
to indicate its sign.
A StringNumericLiteral that is empty or contains only white space is converted to +0.
Infinity
and –Infinity
are recognized as a StringNumericLiteral but not as a NumericLiteral.
The conversion of a String to a Number value is similar overall to the determination of the Number value for a numeric literal (see 11.8.3), but some of the details are different, so the process for converting a String numeric literal to a value of Number type is given here. This value is determined in two steps: first, a mathematical value (MV) is derived from the String numeric literal; second, this mathematical value is rounded as described below. The MV on any grammar symbol, not provided below, is the MV for that symbol defined in 11.8.3.1.
The MV of StringNumericLiteral ::: [empty] is 0.
The MV of StringNumericLiteral ::: StrWhiteSpace is 0.
The MV of StringNumericLiteral ::: StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt is the MV of StrNumericLiteral, no matter whether white space is present or not.
The MV of StrNumericLiteral ::: StrDecimalLiteral is the MV of StrDecimalLiteral.
The MV of StrNumericLiteral ::: BinaryIntegerLiteral is the MV of BinaryIntegerLiteral.
The MV of StrNumericLiteral ::: OctalIntegerLiteral is the MV of OctalIntegerLiteral.
The MV of StrNumericLiteral ::: HexIntegerLiteral is the MV of HexIntegerLiteral.
The MV of StrDecimalLiteral ::: StrUnsignedDecimalLiteral is the MV of StrUnsignedDecimalLiteral.
The MV of StrDecimalLiteral ::: +
StrUnsignedDecimalLiteral is the MV of StrUnsignedDecimalLiteral.
The MV of StrDecimalLiteral ::: -
StrUnsignedDecimalLiteral is the negative of the MV of StrUnsignedDecimalLiteral. (Note that if the MV of StrUnsignedDecimalLiteral is 0, the negative of this MV is also 0. The rounding rule described
below handles the conversion of this signless mathematical zero to a floating-point +0 or −0 as
appropriate.)
The MV of StrUnsignedDecimalLiteral ::: Infinity is 1010000 (a value so large that it will round to +∞).
The MV of StrUnsignedDecimalLiteral ::: DecimalDigits .
is the MV of DecimalDigits.
The MV of StrUnsignedDecimalLiteral ::: DecimalDigits .
DecimalDigits is the MV of
the first DecimalDigits plus (the MV of the second DecimalDigits
times 10−n), where n is the
number of code points in the second DecimalDigits.
The MV of StrUnsignedDecimalLiteral ::: DecimalDigits .
ExponentPart is the MV of
DecimalDigits times 10e, where e is the MV of ExponentPart.
The MV of StrUnsignedDecimalLiteral ::: DecimalDigits .
DecimalDigits ExponentPart is (the MV of the first DecimalDigits plus (the MV of the second
DecimalDigits times 10−n)) times 10e, where n is the number
of code points in the second DecimalDigits and e is the MV of ExponentPart.
The MV of StrUnsignedDecimalLiteral ::: .
DecimalDigits is the MV of DecimalDigits times
10−n, where n is the number of code points in DecimalDigits.
The MV of StrUnsignedDecimalLiteral ::: .
DecimalDigits ExponentPart is the MV of
DecimalDigits times 10e−n, where n is the number of code points in
DecimalDigits and e is the MV of ExponentPart.
The MV of StrUnsignedDecimalLiteral ::: DecimalDigits is the MV of DecimalDigits.
The MV of StrUnsignedDecimalLiteral ::: DecimalDigits ExponentPart is the MV of DecimalDigits times 10e, where e is the MV of ExponentPart.
Once the exact MV for a String numeric literal has been determined, it is then rounded to a value of the Number type.
If the MV is 0, then the rounded value is +0 unless the first non white space code point in the String numeric literal
is ‘-
’, in which case the rounded value is −0. Otherwise, the rounded value must be the
Number value for the MV (in the sense defined in 6.1.6), unless
the literal includes a StrUnsignedDecimalLiteral and the literal has more than 20 significant
digits, in which case the Number value may be either the Number value for the MV of a literal produced by replacing each
significant digit after the 20th with a 0 digit or the Number value for the MV of a literal produced by replacing each
significant digit after the 20th with a 0 digit and then incrementing the literal at the 20th digit position. A digit is
significant if it is not part of an ExponentPart and
0
; orThe abstract operation ToInteger converts argument to an integral numeric value. This abstract operation functions as follows:
The abstract operation ToInt32 converts argument to one of 232 integer values in the range −231 through 231−1, inclusive. This abstract operation functions as follows:
NOTE Given the above definition of ToInt32:
The ToInt32 abstract operation is idempotent: if applied to a result that it produced, the second application leaves that value unchanged.
ToInt32(ToUint32(x)) is equal to ToInt32(x) for all values of x. (It is to preserve this latter property that +∞ and −∞ are mapped to +0.)
ToInt32 maps −0 to +0.
The abstract operation ToUint32 converts argument to one of 232 integer values in the range 0 through 232−1, inclusive. This abstract operation functions as follows:
NOTE Given the above definition of ToUint32:
Step 6 is the only difference between ToUint32 and ToInt32.
The ToUint32 abstract operation is idempotent: if applied to a result that it produced, the second application leaves that value unchanged.
ToUint32(ToInt32(x)) is equal to ToUint32(x) for all values of x. (It is to preserve this latter property that +∞ and −∞ are mapped to +0.)
ToUint32 maps −0 to +0.
The abstract operation ToInt16 converts argument to one of 216 integer values in the range −32768 through 32767, inclusive. This abstract operation functions as follows:
The abstract operation ToUint16 converts argument to one of 216 integer values in the range 0 through 216−1, inclusive. This abstract operation functions as follows:
NOTE Given the above definition of ToUint16:
The abstract operation ToInt8 converts argument to one of 28 integer values in the range −128 through 127, inclusive. This abstract operation functions as follows:
The abstract operation ToUint8 converts argument to one of 28 integer values in the range 0 through 255, inclusive. This abstract operation functions as follows:
The abstract operation ToUint8Clamp converts argument to one of 28 integer values in the range 0 through 255, inclusive. This abstract operation functions as follows:
NOTE Unlike the other ECMAScript integer conversion abstract operation, ToUint8Clamp rounds
rather than truncates non-integer values and does not convert +∞ to 0. ToUint8Clamp does “round half to
even” tie-breaking. This differs from Math.round
which does “round
half up” tie-breaking.
The abstract operation ToString converts argument to a value of type String according to Table 12:
Argument Type | Result |
---|---|
Completion Record | If argument is an abrupt completion, return argument. Otherwise return ToString(argument.[[value]]). |
Undefined | Return "undefined" . |
Null | Return "null" . |
Boolean |
If argument is true, return If argument is false, return |
Number | See 7.1.12.1. |
String | Return argument. |
Symbol | Throw a TypeError exception. |
Object |
Apply the following steps: 1. Let primValue be ToPrimitive(argument, hint String). 2. Return ToString(primValue). |
The abstract operation ToString converts a Number m to String format as follows:
"NaN"
."0"
."-"
and ToString(−m)."Infinity"
.NOTE 1 The following observations may be useful as guidelines for implementations, but are not part of the normative requirements of this Standard:
NOTE 2 For implementations that provide more accurate conversions than required by the rules above, it is recommended that the following alternative version of step 5 be used as a guideline:
5. Otherwise, let n, k, and s be integers such that k ≥ 1, 10k−1 ≤ s < 10k, the Number value for s × 10n−k is m, and k is as small as possible. If there are multiple possibilities for s, choose the value of s for which s × 10n−k is closest in value to m. If there are two such possible values of s, choose the one that is even. Note that k is the number of digits in the decimal representation of s and that s is not divisible by 10.
NOTE 3 Implementers of ECMAScript may find useful the paper and code written by David M. Gay for binary-to-decimal conversion of floating-point numbers:
Gay, David M. Correctly Rounded Binary-Decimal and Decimal-Binary Conversions. Numerical Analysis, Manuscript 90-10.
AT&T Bell Laboratories (Murray Hill, New Jersey). November 30, 1990. Available as
http://cm.bell-labs.com/cm/cs/doc/90/4-10.ps.gz. Associated
code available as
http://netlib.sandia.gov/fp/dtoa.c and as
http://netlib.sandia.gov/fp/g_fmt.c and may also be found at the various
netlib
mirror sites.
The abstract operation ToObject converts argument to a value of type Object according to Table 13:
Argument Type | Result |
---|---|
Completion Record | If argument is an abrupt completion, return argument. Otherwise return ToObject(argument.[[value]]). |
Undefined | Throw a TypeError exception. |
Null | Throw a TypeError exception. |
Boolean | Return a new Boolean object whose [[BooleanData]] internal slot is set to the value of argument. See 19.3 for a description of Boolean objects. |
Number | Return a new Number object whose [[NumberData]] internal slot is set to the value of argument. See 20.1 for a description of Number objects. |
String | Return a new String object whose [[StringData]] internal slot is set to the value of argument. See 21.1 for a description of String objects. |
Symbol | Return a new Symbol object whose [[SymbolData]] internal slot is set to the value of argument. See 19.4 for a description of Symbol objects. |
Object | Return argument. |
The abstract operation ToPropertyKey converts argument to a value that can be used as a property key by performing the following steps:
The abstract operation ToLength converts argument to an integer suitable for use as the length of an array-like object. It performs the following steps:
The abstract operation CanonicalNumericIndexString returns argument converted to a
numeric value if it is a String representation of a Number that would be produced by ToString,
or the string "-0"
. Otherwise, it returns undefined. This abstract operation
functions as follows:
"-0"
, return −0.A canonical numeric string is any String value for which the CanonicalNumericIndexString abstract operation does not return undefined.
The abstract operation RequireObjectCoercible throws an error if argument is a value that cannot be converted to an Object using ToObject. It is defined by Table 14:
Argument Type | Result |
---|---|
Completion Record | If argument is an abrupt completion, return argument. Otherwise return RequireObjectCoercible(argument.[[value]]). |
Undefined | Throw a TypeError exception. |
Null | Throw a TypeError exception. |
Boolean | Return argument. |
Number | Return argument. |
String | Return argument. |
Symbol | Return argument. |
Object | Return argument. |
The abstract operation IsArray takes one argument argument, and performs the following steps:
The abstract operation IsCallable determines if argument, which must be an ECMAScript language value or a Completion Record, is a callable function with a [[Call]] internal method.
The abstract operation IsConstructor determines if argument, which must be an ECMAScript language value or a Completion Record, is a function object with a [[Construct]] internal method.
The abstract operation IsExtensible is used to determine whether additional properties can be added to the object that is O. A Boolean value is returned. This abstract operation performs the following steps:
The abstract operation IsInteger determines if argument is a finite integer numeric value.
The abstract operation IsPropertyKey determines if argument, which must be an ECMAScript language value or a Completion Record, is a value that may be used as a property key.
The abstract operation IsRegExp with argument argument performs the following steps:
The internal comparison abstract operation SameValue(x, y), where x and y are ECMAScript language values, produces true or false. Such a comparison is performed as follows:
NOTE This algorithm differs from the Strict Equality Comparison Algorithm (7.2.13) in its treatment of signed zeroes and NaNs.
The internal comparison abstract operation SameValueZero(x, y), where x and y are ECMAScript language values, produces true or false. Such a comparison is performed as follows:
NOTE SameValueZero differs from SameValue only in its treatment of +0 and −0.
The comparison x < y, where x and y are values, produces true, false, or undefined (which indicates that at least one operand is NaN). In addition to x and y the algorithm takes a Boolean flag named LeftFirst as a parameter. The flag is used to control the order in which operations with potentially visible side-effects are performed upon x and y. It is necessary because ECMAScript specifies left to right evaluation of expressions. The default value of LeftFirst is true and indicates that the x parameter corresponds to an expression that occurs to the left of the y parameter’s corresponding expression. If LeftFirst is false, the reverse is the case and operations must be performed upon y before x. Such a comparison is performed as follows:
NOTE 1 Step 5 differs from step 11 in the algorithm for the addition operator +
(12.7.3) in using “and” instead of “or”.
NOTE 2 The comparison of Strings uses a simple lexicographic ordering on sequences of code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore String values that are canonically equal according to the Unicode standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized form. Also, note that for strings containing supplementary characters, lexicographic ordering on sequences of UTF-16 code unit values differs from that on sequences of code point values.
The comparison x == y, where x and y are values, produces true or false. Such a comparison is performed as follows:
The comparison x === y, where x and y are values, produces true or false. Such a comparison is performed as follows:
NOTE This algorithm differs from the SameValue Algorithm (7.2.9) in its treatment of signed zeroes and NaNs.
The abstract operation Get is used to retrieve the value of a specific property of an object. The operation is called with arguments O and P where O is the object and P is the property key. This abstract operation performs the following steps:
The abstract operation GetV is used to retrieve the value of a specific property of an ECMAScript language value. If the value is not an object, the property lookup is performed using a wrapper object appropriate for the type of the value. The operation is called with arguments V and P where V is the value and P is the property key. This abstract operation performs the following steps:
The abstract operation Set is used to set the value of a specific property of an object. The operation is called with arguments O, P, V, and Throw where O is the object, P is the property key, V is the new value for the property and Throw is a Boolean flag. This abstract operation performs the following steps:
The abstract operation CreateDataProperty is used to create a new own property of an object. The operation is called with arguments O, P, and V where O is the object, P is the property key, and V is the value for the property. This abstract operation performs the following steps:
NOTE This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or if O is not extensible, [[DefineOwnProperty]] will return false.
The abstract operation CreateMethodProperty is used to create a new own property of an object. The operation is called with arguments O, P, and V where O is the object, P is the property key, and V is the value for the property. This abstract operation performs the following steps:
NOTE This abstract operation creates a property whose attributes are set to the same defaults used for built-in methods and methods defined using class declaration syntax. Normally, the property will not already exist. If it does exist and is not configurable or if O is not extensible, [[DefineOwnProperty]] will return false.
The abstract operation CreateDataPropertyOrThrow is used to create a new own property of an object. It throws a TypeError exception if the requested property update cannot be performed. The operation is called with arguments O, P, and V where O is the object, P is the property key, and V is the value for the property. This abstract operation performs the following steps:
NOTE This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or if O is not extensible, [[DefineOwnProperty]] will return false causing this operation to throw a TypeError exception.
The abstract operation DefinePropertyOrThrow is used to call the [[DefineOwnProperty]] internal method of an object in a manner that will throw a TypeError exception if the requested property update cannot be performed. The operation is called with arguments O, P, and desc where O is the object, P is the property key, and desc is the Property Descriptor for the property. This abstract operation performs the following steps:
The abstract operation DeletePropertyOrThrow is used to remove a specific own property of an object. It throws an exception if the property is not configurable. The operation is called with arguments O and P where O is the object and P is the property key. This abstract operation performs the following steps:
The abstract operation GetMethod is used to get the value of a specific property of an object when the value of the property is expected to be a function. The operation is called with arguments O and P where O is the object, P is the property key. This abstract operation performs the following steps:
The abstract operation HasProperty is used to determine whether an object has a property with the specified property key. The property may be either an own or inherited. A Boolean value is returned. The operation is called with arguments O and P where O is the object and P is the property key. This abstract operation performs the following steps:
The abstract operation HasOwnProperty is used to determine whether an object has an own property with the specified property key. A Boolean value is returned. The operation is called with arguments O and P where O is the object and P is the property key. This abstract operation performs the following steps:
The abstract operation Call is used to call the [[Call]] internal method of a function object. The operation is called with arguments F, V , and optionally argumentsList where F is the function object, V is an ECMAScript language value that is the this value of the [[Call]], and argumentsList is the value passed to the corresponding argument of the internal method. If argumentsList is not present, an empty List is used as its value. This abstract operation performs the following steps:
The abstract operation Construct is used to call the [[Construct]] internal method of a function object. The operation is called with arguments F, and optionally argumentsList, and newTarget where F is the function object. argumentsList and newTarget are the values to be passed as the corresponding arguments of the internal method. If argumentsList is not present, an empty List is used as its value. If newTarget is not present, F is used as its value. This abstract operation performs the following steps:
NOTE If newTarget is not passed, this operation is equivalent to: new
F(...argumentsList)
The abstract operation SetIntegrityLevel is used to fix the set of own properties of an object. This abstract operation performs the following steps:
"sealed"
or
"frozen"
."sealed"
, then
"frozen"
,
The abstract operation TestIntegrityLevel is used to determine if the set of own properties of an object are fixed. This abstract operation performs the following steps:
"sealed"
or
"frozen"
."frozen"
and IsDataDescriptor(currentDesc) is true, then
The abstract operation CreateArrayFromList is used to create an Array object whose elements are provided by a List. This abstract operation performs the following steps:
The abstract operation CreateListFromArrayLike is used to create a List value whose elements are provided by the indexed properties of an array-like object, obj. The optional argument elementTypes is a List containing the names of ECMAScript Language Types that are allowed for element values of the List that is created. This abstract operation performs the following steps:
"length"
)).The abstract operation Invoke is used to call a method property of an object. The operation is called with arguments O, P , and optionally argumentsList where O serves as both the lookup point for the property and the this value of the call, P is the property key, and argumentsList is the list of arguments values passed to the method. If argumentsList is not present, an empty List is used as its value. This abstract operation performs the following steps:
The abstract operation OrdinaryHasInstance implements the default algorithm for determining if an object O inherits from the instance object inheritance path provided by constructor C. This abstract operation performs the following steps:
"prototype"
).null
, return false.The abstract operation SpeciesConstructor is used to retrieve the constructor that should be used to create new objects that are derived from the argument object O. The defaultConstructor argument is the constructor to use if a constructor @@species property cannot be found starting from O. This abstract operation performs the following steps:
"constructor"
).When the abstract operation EnumerableOwnNames is called with Object O the following steps are taken:
NOTE The order of elements in the returned list is the same as the enumeration order that is used by a for-in statement.
The abstract operation GetFunctionRealm with argument obj performs the following steps:
NOTE Step 5 will only be reached if target is a non-standard exotic function object that does not have a [[Realm]] internal slot.
The abstract operation GetIterator with argument obj and optional argument method performs the following steps:
The abstract operation IteratorNext with argument iterator and optional argument value performs the following steps:
"next"
, «
»)."next"
,
«value»).The abstract operation IteratorComplete with argument iterResult performs the following steps:
The abstract operation IteratorValue with argument iterResult performs the following steps:
The abstract operation IteratorStep with argument iterator requests the next value from iterator and returns either false indicating that the iterator has reached its end or the IteratorResult object if a next value is available. IteratorStep performs the following steps:
The abstract operation IteratorClose with arguments iterator and completion is used to notify an iterator that it should perform any actions it would normally perform when it has reached its completed state:
"return"
).The abstract operation CreateIterResultObject with arguments value and done creates an object that supports the IteratorResult interface by performing the following steps:
"value"
, value)."done"
, done).The abstract operation CreateListIterator with argument list creates an Iterator (25.1.1.2) object whose next method returns the successive elements of list. It performs the following steps:
next
(7.4.8.1)."next"
,
next).The ListIterator next
method is a standard built-in function object (clause 17) that performs the following steps:
NOTE A ListIterator next
method will throw an exception if applied to any object
other than the one with which it was originally associated.
A Lexical Environment is a specification type used to define the association of Identifiers to specific variables and functions based upon the lexical nesting structure of ECMAScript code. A Lexical Environment consists of an Environment Record and a possibly null reference to an outer Lexical Environment. Usually a Lexical Environment is associated with some specific syntactic structure of ECMAScript code such as a FunctionDeclaration, a BlockStatement, or a Catch clause of a TryStatement and a new Lexical Environment is created each time such code is evaluated.
An Environment Record records the identifier bindings that are created within the scope of its associated Lexical Environment. It is referred to as the Lexical Environment’s EnvironmentRecord
The outer environment reference is used to model the logical nesting of Lexical Environment values. The outer reference of a (inner) Lexical Environment is a reference to the Lexical Environment that logically surrounds the inner Lexical Environment. An outer Lexical Environment may, of course, have its own outer Lexical Environment. A Lexical Environment may serve as the outer environment for multiple inner Lexical Environments. For example, if a FunctionDeclaration contains two nested FunctionDeclarations then the Lexical Environments of each of the nested functions will have as their outer Lexical Environment the Lexical Environment of the current evaluation of the surrounding function.
A global environment is a Lexical Environment which does not have an outer environment. The global
environment’s outer environment reference is null. A global environment’s EnvironmentRecord may be
prepopulated with identifier bindings and includes an associated global object whose properties provide some of the global environment’s identifier bindings. This global object is the
value of a global environment’s this
binding. As ECMAScript code is executed, additional properties may
be added to the global object and the initial properties may be modified.
A module environment is a Lexical Environment that contains the bindings for the top level declarations of a Module. It also contains the bindings that are explicitly imported by the Module. The outer environment of a module environment is a global environment.
A function environment is a Lexical Environment that corresponds to the invocation of an ECMAScript function object. A function environment may establish a new
this
binding. A function environment also captures the state necessary to support super
method
invocations.
Lexical Environments and Environment Record values are purely specification mechanisms and need not correspond to any specific artefact of an ECMAScript implementation. It is impossible for an ECMAScript program to directly access or manipulate such values.
There are two primary kinds of Environment Record values used in this specification: declarative Environment Records and object Environment Records. Declarative Environment Records are used to define the effect of ECMAScript language syntactic elements such as FunctionDeclarations, VariableDeclarations, and Catch clauses that directly associate identifier bindings with ECMAScript language values. Object Environment Records are used to define the effect of ECMAScript elements such as WithStatement that associate identifier bindings with the properties of some object. Global Environment Records and function Environment Records are specializations that are used for specifically for Script global declarations and for top-level declarations within functions.
For specification purposes Environment Record values are values of the Record specification type and can be thought of as existing in a simple object-oriented hierarchy where Environment Record is an abstract class with three concrete subclasses, declarative Environment Record, object Environment Record, and global Environment Record. Function Environment Records and module Environment Records are subclasses of declarative Environment Record. The abstract class includes the abstract specification methods defined in Table 15. These abstract methods have distinct concrete algorithms for each of the concrete subclasses.
Method | Purpose |
---|---|
HasBinding(N) | Determine if an Environment Record has a binding for the String value N. Return true if it does and false if it does not |
CreateMutableBinding(N, D) | Create a new but uninitialized mutable binding in an Environment Record. The String value N is the text of the bound name. If the optional Boolean argument D is true the binding is may be subsequently deleted. |
CreateImmutableBinding(N, S) | Create a new but uninitialized immutable binding in an Environment Record. The String value N is the text of the bound name. If S is true then attempts to access the value of the binding before it is initialized or set it after it has been initialized will always throw an exception, regardless of the strict mode setting of operations that reference that binding. S is an optional parameter that defaults to false. |
InitializeBinding(N,V) | Set the value of an already existing but uninitialized binding in an Environment Record. The String value N is the text of the bound name. V is the value for the binding and is a value of any ECMAScript language type. |
SetMutableBinding(N,V, S) | Set the value of an already existing mutable binding in an Environment Record. The String value N is the text of the bound name. V is the value for the binding and may be a value of any ECMAScript language type. S is a Boolean flag. If S is true and the binding cannot be set throw a TypeError exception. |
GetBindingValue(N,S) | Returns the value of an already existing binding from an Environment Record. The String value N is the text of the bound name. S is used to identify references originating in strict mode code or that otherwise require strict mode reference semantics. If S is true and the binding does not exist throw a ReferenceError exception. If the binding exists but is uninitialized a ReferenceError is thrown, regardless of the value of S. |
DeleteBinding(N) | Delete a binding from an Environment Record. The String value N is the text of the bound name. If a binding for N exists, remove the binding and return true. If the binding exists but cannot be removed return false. If the binding does not exist return true. |
HasThisBinding() | Determine if an Environment Record establishes a this binding. Return true if it does and false if it does not. |
HasSuperBinding() | Determine if an Environment Record establishes a super method binding. Return true if it does and false if it does not. |
WithBaseObject () | If this Environment Record is associated with a with statement, return the with object. Otherwise, return undefined. |
Each declarative Environment Record is associated with an ECMAScript program scope containing variable, constant, let, class, module, import, and/or function declarations. A declarative Environment Record binds the set of identifiers defined by the declarations contained within its scope.
The behaviour of the concrete specification methods for declarative Environment Records is defined by the following algorithms.
The concrete Environment Record method HasBinding for declarative Environment Records simply determines if the argument identifier is one of the identifiers bound by the record:
The concrete Environment Record method CreateMutableBinding for declarative Environment Records creates a new mutable binding for the name N that is uninitialized. A binding must not already exist in this Environment Record for N. If Boolean argument D is provided and has the value true the new binding is marked as being subject to deletion.
The concrete Environment Record method CreateImmutableBinding for declarative Environment Records creates a new immutable binding for the name N that is uninitialized. A binding must not already exist in this Environment Record for N. If Boolean argument S is provided and has the value true the new binding is marked as a strict binding.
The concrete Environment Record method InitializeBinding for declarative Environment Records is used to set the bound value of the current binding of the identifier whose name is the value of the argument N to the value of argument V. An uninitialized binding for N must already exist.
The concrete Environment Record method SetMutableBinding for declarative Environment Records attempts to change the bound value of the current binding of the identifier whose name is the value of the argument N to the value of argument V. A binding for N normally already exist, but in rare cases it may not. If the binding is an immutable binding, a TypeError is thrown if S is true.
NOTE An example of ECMAScript code that results in a missing binding at step 2 is:
function f(){eval("var x; x = (delete x, 0);")}
The concrete Environment Record method GetBindingValue for declarative Environment Records simply returns the value of its bound identifier whose name is the value of the argument N. If the binding exists but is uninitialized a ReferenceError is thrown, regardless of the value of S.
The concrete Environment Record method DeleteBinding for declarative Environment Records can only delete bindings that have been explicitly designated as being subject to deletion.
Regular declarative Environment Records do not provide a this
binding.
Regular declarative Environment Records do not provide a super
binding.
Declarative Environment Records always return undefined as their WithBaseObject.
Each object Environment Record is associated with an object called its binding object. An object Environment Record binds the set of string identifier names that directly correspond to the property names of its binding object. Property keys that are not strings in the form of an IdentifierName are not included in the set of bound identifiers. Both own and inherited properties are included in the set regardless of the setting of their [[Enumerable]] attribute. Because properties can be dynamically added and deleted from objects, the set of identifiers bound by an object Environment Record may potentially change as a side-effect of any operation that adds or deletes properties. Any bindings that are created as a result of such a side-effect are considered to be a mutable binding even if the Writable attribute of the corresponding property has the value false. Immutable bindings do not exist for object Environment Records.
Object Environment Records created for with
statements (13.11) can
provide their binding object as an implicit this value for use in function calls. The capability is controlled by
a withEnvironment Boolean value that is associated with each object Environment Record. By default, the value of withEnvironment is
false for any object Environment Record.
The behaviour of the concrete specification methods for object Environment Records is defined by the following algorithms.
The concrete Environment Record method HasBinding for object Environment Records determines if its associated binding object has a property whose name is the value of the argument N:
The concrete Environment Record method CreateMutableBinding for object Environment Records creates in an Environment Record’s associated binding object a property whose name is the String value and initializes it to the value undefined. If Boolean argument D is provided and has the value true the new property’s [[Configurable]] attribute is set to true, otherwise it is set to false.
NOTE Normally envRec will not have a binding for N but if it does, the semantics of DefinePropertyOrThrow may result in an existing binding being replaced or shadowed or cause an abrupt completion to be returned.
The concrete Environment Record method CreateImmutableBinding is never used within this specification in association with Object Environment Records.
The concrete Environment Record method InitializeBinding for object Environment Records is used to set the bound value of the current binding of the identifier whose name is the value of the argument N to the value of argument V. An uninitialized binding for N must already exist.
NOTE In this specification, all uses of CreateMutableBinding for object Environment Records are immediately followed by a call to InitializeBinding for the same name. Hence, implementations do not need to explicitly track the initialization state of individual object Environment Record bindings.
The concrete Environment Record method SetMutableBinding for object Environment Records attempts to set the value of the Environment Record’s associated binding object’s property whose name is the value of the argument N to the value of argument V. A property named N normally already exists but if it does not or is not currently writable, error handling is determined by the value of the Boolean argument S.
The concrete Environment Record method GetBindingValue for object Environment Records returns the value of its associated binding object’s property whose name is the String value of the argument identifier N. The property should already exist but if it does not the result depends upon the value of the S argument:
The concrete Environment Record method DeleteBinding for object Environment Records can only delete bindings that correspond to properties of the environment object whose [[Configurable]] attribute have the value true.
Regular object Environment Records do not provide a this
binding.
Regular object Environment Records do not provide a super
binding.
Object Environment Records return undefined as their WithBaseObject unless their withEnvironment flag is true.
A function Environment Record is a declarative Environment Record that is used to represent the top-level scope of a function and,
if the function is not an ArrowFunction, provides a this
binding. If a function is
not an ArrowFunction function and references super
, its function Environment Record also contains the state that is used to perform
super
method invocations from within the function.
Function Environment Records have the additional state fields listed in Table 16.
Field Name | Value | Meaning |
---|---|---|
[[thisValue]] | Any | This is the this value used for this invocation of the function. |
[[thisBindingStatus]] | "lexical" | "initialized" | "uninitialized" |
If the value is "lexical" , this is an ArrowFunction and does not have a local this value. |
[[FunctionObject]] | Object | The function Object whose invocation caused this Environment Record to be created. |
[[HomeObject]] | Object | undefined | If the associated function has super property accesses and is not an ArrowFunction, [[HomeObject]] is the object that the function is bound to as a method. The default value for [[HomeObject]] is undefined. |
[[NewTarget]] | Object | undefined | If this Environment Record was created by the [[Construct]] internal method, [[NewTarget]] is the value of the [[Construct]] newTarget parameter. Otherwise, its value is undefined. |
Function Environment Records support all of the declarative Environment Record methods listed in Table 15 and share the same specifications for all of those methods except for HasThisBinding and HasSuperBinding. In addition, function Environment Records support the methods listed in Table 17:
Method | Purpose |
---|---|
BindThisValue(V) | Set the [[thisValue]] and record that it has been initialized. |
GetThisBinding() | Return the value of this Environment Record’s this binding. Throws a ReferenceError if the this binding has not been initialized. |
GetSuperBase() | Return the object that is the base for super property accesses bound in this Environment Record. The object is derived from this Environment Record’s [[HomeObject]] field. The value undefined indicates that super property accesses will produce runtime errors. |
The behaviour of the additional concrete specification methods for function Environment Records is defined by the following algorithms:
"lexical"
."initialized"
, throw a ReferenceError
exception."initialized"
."lexical"
, return false; otherwise, return
true."lexical"
, return false."lexical"
."uninitialized"
, throw a ReferenceError
exception.A global Environment Record is used to represent the outer most scope that is shared by all of the ECMAScript Script elements that are processed in a common Realm (8.2). A global Environment Record provides the bindings for built-in globals (clause 18), properties of the global object, and for all top-level declarations (13.2.8, 13.2.10) that occur within a Script.
A global Environment Record is logically a single record but it is specified as a composite encapsulating an object Environment Record and a declarative Environment Record. The object Environment Record has as its base object the global object of the associated Realm. This global object is the value returned by the global Environment Record’s GetThisBinding concrete method. The object Environment Record component of a global Environment Record contains the bindings for all built-in globals (clause 18) and all bindings introduced by a FunctionDeclaration, GeneratorDeclaration, or VariableStatement contained in global code. The bindings for all other ECMAScript declarations in global code are contained in the declarative Environment Record component of the global Environment Record.
Properties may be created directly on a global object. Hence, the object Environment Record component of a global Environment Record may contain both bindings created explicitly by FunctionDeclaration, GeneratorDeclaration, or VariableDeclaration declarations and binding created implicitly as properties of the global object. In order to identify which bindings were explicitly created using declarations, a global Environment Record maintains a list of the names bound using its CreateGlobalVarBindings and CreateGlobalFunctionBindings concrete methods.
Global Environment Records have the additional fields listed in Table 18 and the additional methods listed in Table 19.
Field Name | Value | Meaning |
---|---|---|
[[ObjectRecord]] | Object Environment Record | Binding object is the global object. It contains global built-in bindings as well as FunctionDeclaration, GeneratorDeclaration, and VariableDeclaration bindings in global code for the associated Realm. |
[[DeclarativeRecord]] | Declarative Environment Record | Contains bindings for all declarations in global code for the associated Realm code except for FunctionDeclaration, GeneratorDeclaration, and VariableDeclaration bindings. |
[[VarNames]] | List of String | The string names bound by FunctionDeclaration, GeneratorDeclaration, and VariableDeclaration declarations in global code for the associated Realm. |
Method | Purpose |
---|---|
GetThisBinding() | Return the value of this Environment Record’s this binding. |
HasVarDeclaration (N) | Determines if the argument identifier has a binding in this Environment Record that was created using a VariableDeclaration, FunctionDeclaration, or GeneratorDeclaration. |
HasLexicalDeclaration (N) | Determines if the argument identifier has a binding in this Environment Record that was created using a lexical declaration such as a LexicalDeclaration or a ClassDeclaration. |
HasRestrictedGlobalProperty (N) | Determines if the argument is the name of a global object property that may not be shadowed by a global lexically binding. |
CanDeclareGlobalVar (N) | Determines if a corresponding CreateGlobalVarBinding call would succeed if called for the same argument N. |
CanDeclareGlobalFunction (N) | Determines if a corresponding CreateGlobalFunctionBinding call would succeed if called for the same argument N. |
CreateGlobalVarBinding(N, D) | Used to create and initialize to undefined a global var binding in the [[ObjectRecord]] component of a global Environment Record. The binding will be a mutable binding. The corresponding global object property will have attribute values appropriate for a var . The String value N is the bound name. If D is true the binding may be deleted. Logically equivalent to CreateMutableBinding followed by a SetMutableBinding but it allows var declarations to receive special treatment. |
CreateGlobalFunctionBinding(N, V, D) | Create and initialize a global function binding in the [[ObjectRecord]] component of a global Environment Record. The binding will be a mutable binding. The corresponding global object property will have attribute values appropriate for a function . The String value N is the bound name. V is the initialization value. If the optional Boolean argument D is true the binding is may be deleted. Logically equivalent to CreateMutableBinding followed by a SetMutableBinding but it allows function declarations to receive special treatment. |
The behaviour of the concrete specification methods for global Environment Records is defined by the following algorithms.
The concrete Environment Record method HasBinding for global Environment Records simply determines if the argument identifier is one of the identifiers bound by the record:
The concrete Environment Record method CreateMutableBinding for global Environment Records creates a new mutable binding for the name N that is uninitialized. The binding is created in the associated DeclarativeRecord. A binding for N must not already exist in the DeclarativeRecord. If Boolean argument D is provided and has the value true the new binding is marked as being subject to deletion.
The concrete Environment Record method CreateImmutableBinding for global Environment Records creates a new immutable binding for the name N that is uninitialized. A binding must not already exist in this Environment Record for N. If Boolean argument S is provided and has the value true the new binding is marked as a strict binding.
The concrete Environment Record method InitializeBinding for global Environment Records is used to set the bound value of the current binding of the identifier whose name is the value of the argument N to the value of argument V. An uninitialized binding for N must already exist.
The concrete Environment Record method SetMutableBinding for global Environment Records attempts to change the bound value of the current binding of the identifier whose name is the value of the argument N to the value of argument V. If the binding is an immutable binding, a TypeError is thrown if S is true. A property named N normally already exists but if it does not or is not currently writable, error handling is determined by the value of the Boolean argument S.
The concrete Environment Record method GetBindingValue for global Environment Records returns the value of its bound identifier whose name is the value of the argument N. If the binding is an uninitialized binding throw a ReferenceError exception. A property named N normally already exists but if it does not or is not currently writable, error handling is determined by the value of the Boolean argument S.
The concrete Environment Record method DeleteBinding for global Environment Records can only delete bindings that have been explicitly designated as being subject to deletion.
Global Environment Records always provide a
this
binding whose value is the associated global object.
Global Environment Records always return undefined as their WithBaseObject.
The concrete Environment Record method HasVarDeclaration for global Environment Records determines if the argument identifier has a binding in this record that was created using a VariableStatement or a FunctionDeclaration :
The concrete Environment Record method HasLexicalDeclaration for global Environment Records determines if the argument identifier has a binding in this record that was created using a lexical declaration such as a LexicalDeclaration or a ClassDeclaration :
The concrete Environment Record method HasRestrictedGlobalProperty for global Environment Records determines if the argument identifier is the name of a property of the global object that must not be shadowed by a global lexically binding:
NOTE Properties may exist upon a global object that were directly created rather than being
declared using a var or function declaration. A global lexical binding may not be created that has the same name as a
non-configurable property of the global object. The global property undefined
is an example of such a
property.
The concrete Environment Record method CanDeclareGlobalVar for global Environment Records determines if a corresponding CreateGlobalVarBinding call would succeed if called for the same argument N. Redundant var declarations and var declarations for pre-existing global object properties are allowed.
The concrete Environment Record method CanDeclareGlobalFunction for global Environment Records determines if a corresponding CreateGlobalFunctionBinding call would succeed if called for the same argument N.
The concrete Environment Record method CreateGlobalVarBinding for global Environment Records creates and initializes a mutable binding in the associated object Environment Record and records the bound name in the associated [[VarNames]] List. If a binding already exists, it is reused and assumed to be initialized.
The concrete Environment Record method CreateGlobalFunctionBinding for global Environment Records creates and initializes a mutable binding in the associated object Environment Record and records the bound name in the associated [[VarNames]] List. If a binding already exists, it is replaced.
NOTE Global function declarations are always represented as own properties of the global object. If possible, an existing own property is reconfigured to have a standard set of attribute values. Steps 10-12 are equivalent to what calling the InitializeBinding concrete method would do and if globalObject is a Proxy will produce the same sequence of Proxy trap calls.
A module Environment Record is a declarative Environment Record that is used to represent the outer scope of an ECMAScript Module. In additional to normal mutable and immutable bindings, module Environment Records also provide immutable import bindings which are bindings that provide indirect access to a target binding that exists in another Environment Record.
Module Environment Records support all of the declarative Environment Record methods listed in Table 15 and share the same specifications for all of those methods except for GetBindingValue, DeleteBinding, HasThisBinding and GetThisBinding. In addition, module Environment Records support the methods listed in Table 20:
Method | Purpose |
---|---|
CreateImportBinding(N, M, N2 ) | Create an immutable indirect binding in a module Environment Record. The String value N is the text of the bound name. M is a Module Record (see 15.2.1.15), and N2 is a binding that exists in M’s module Environment Record. |
GetThisBinding() | Return the value of this Environment Record’s this binding. |
The behaviour of the additional concrete specification methods for module Environment Records are defined by the following algorithms:
The concrete Environment Record method GetBindingValue for module Environment Records returns the value of its bound identifier whose name is the value of the argument N. However, if the binding is an indirect binding the value of the target binding is returned. If the binding exists but is uninitialized a ReferenceError is thrown, regardless of the value of S.
NOTE Because a Module is always strict mode code, calls to GetBindingValue should always pass true as the value of S.
The concrete Environment Record method DeleteBinding for module Environment Records refuses to delete bindings.
NOTE The bindings of a module Environment Record are not deletable.
Module Environment Records provide a this
binding.
The concrete Environment Record method CreateImportBinding for module Environment Records creates a new initialized immutable indirect binding for the name N. A binding must not already exist in this Environment Record for N. M is a Module Record (see 15.2.1.15), and N2 is the name of a binding that exists in M’s module Environment Record. Accesses to the value of the new binding will indirectly access the bound value of value of the target binding.
The following abstract operations are used in this specification to operate upon lexical environments:
The abstract operation GetIdentifierReference is called with a Lexical Environment lex, a String name, and a Boolean flag strict. The value of lex may be null. When called, the following steps are performed:
When the abstract operation NewDeclarativeEnvironment is called with a Lexical Environment as argument E the following steps are performed:
When the abstract operation NewObjectEnvironment is called with an Object O and a Lexical Environment E as arguments, the following steps are performed:
When the abstract operation NewFunctionEnvironment is called with arguments F and newTarget the following steps are performed:
"lexical"
."uninitialized"
.When the abstract operation NewGlobalEnvironment is called with an ECMAScript Object G as its argument, the following steps are performed:
When the abstract operation NewModuleEnvironment is called with a Lexical Environment argument E the following steps are performed:
Before it is evaluated, all ECMAScript code must be associated with a Realm. Conceptually, a realm consists of a set of intrinsic objects, an ECMAScript global environment, all of the ECMAScript code that is loaded within the scope of that global environment, and other associated state and resources.
A Realm is specified as a Record with the fields specified in Table 21:
Field Name | Value | Meaning |
---|---|---|
[[intrinsics]] | Record whose field names are intrinsic keys and whose values are objects | These are the intrinsic values used by code associated with this Realm |
[[globalThis]] | Object | The global object for this Realm |
[[globalEnv]] | Lexical Environment | The global environment for this Realm |
[[templateMap]] | A List of Record { [[strings]]: List, [[array]]: Object}. | Template objects are canonicalized separately for each Realm using its [[templateMap]]. Each [[strings]] value is a List containing, in source text order, the raw String values of a TemplateLiteral that has been evaluated. The associated [[array]] value is the corresponding template object that is passed to a tag function. |
An implementation may define other, implementation specific fields.
The abstract operation CreateRealm with no arguments performs the following steps:
When the abstract operation CreateIntrinsics with argument realmRec performs the following steps:
The abstract operation SetRealmGlobalObject with arguments realmRec and globalObj performs the following steps:
The abstract operation SetDefaultGlobalBindings with argument realmRec performs the following steps:
An execution context is a specification device that is used to track the runtime evaluation of code by an ECMAScript implementation. At any point in time, there is at most one execution context that is actually executing code. This is known as the running execution context. A stack is used to track execution contexts. The running execution context is always the top element of this stack. A new execution context is created whenever control is transferred from the executable code associated with the currently running execution context to executable code that is not associated with that execution context. The newly created execution context is pushed onto the stack and becomes the running execution context.
An execution context contains whatever implementation specific state is necessary to track the execution progress of its associated code. Each execution context has at least the state components listed in Table 22.
Component | Purpose |
---|---|
code evaluation state | Any state needed to perform, suspend, and resume evaluation of the code associated with this execution context. |
Function | If this execution context is evaluating the code of a function object, then the value of this component is that function object. If the context is evaluating the code of a Script or Module, the value is null. |
Realm | The Realm from which associated code accesses ECMAScript resources. |
Evaluation of code by the running execution context may be suspended at various points defined within this specification. Once the running execution context has been suspended a different execution context may become the running execution context and commence evaluating its code. At some later time a suspended execution context may again become the running execution context and continue evaluating its code at the point where it had previously been suspended. Transition of the running execution context status among execution contexts usually occurs in stack-like last-in/first-out manner. However, some ECMAScript features require non-LIFO transitions of the running execution context.
The value of the Realm component of the running execution context is also called the current Realm. The value of the Function component of the running execution context is also called the active function object.
Execution contexts for ECMAScript code have the additional state components listed in Table 23.
Component | Purpose |
---|---|
LexicalEnvironment | Identifies the Lexical Environment used to resolve identifier references made by code within this execution context. |
VariableEnvironment | Identifies the Lexical Environment whose EnvironmentRecord holds bindings created by VariableStatements within this execution context. |
The LexicalEnvironment and VariableEnvironment components of an execution context are always Lexical Environments. When an execution context is created its LexicalEnvironment and VariableEnvironment components initially have the same value.
Execution contexts representing the evaluation of generator objects have the additional state components listed in Table 24.
Component | Purpose |
---|---|
Generator | The GeneratorObject that this execution context is evaluating. |
In most situations only the running execution context (the top of the execution context stack) is directly manipulated by algorithms within this specification. Hence when the terms “LexicalEnvironment”, and “VariableEnvironment” are used without qualification they are in reference to those components of the running execution context.
An execution context is purely a specification mechanism and need not correspond to any particular artefact of an ECMAScript implementation. It is impossible for ECMAScript code to directly access or observe an execution context.
The ResolveBinding abstract operation is used to determine the binding of name passed as a String value. The optional argument env can be used to explicitly provide the Lexical Environment that is to be searched for the binding. During execution of ECMAScript code, ResolveBinding is performed using the following algorithm:
NOTE The result of ResolveBinding is always a Reference value with its referenced name component equal to the name argument.
The abstract operation GetThisEnvironment finds
the Environment Record that currently supplies the binding of the keyword
this
. GetThisEnvironment performs the following steps:
NOTE The loop in step 2 will always terminate because the list of environments always ends with
the global environment which has a this
binding.
The abstract operation ResolveThisBinding determines the binding of the keyword this
using the LexicalEnvironment of the running
execution context. ResolveThisBinding performs the following steps:
The abstract operation GetNewTarget determines the NewTarget value using the LexicalEnvironment of the running execution context. GetNewTarget performs the following steps:
The abstract operation GetGlobalObject returns the global object used by the currently running execution context. GetGlobalObject performs the following steps:
A Job is an abstract operation that initiates an ECMAScript computation when no other ECMAScript computation is currently in progress. A Job abstract operation may be defined to accept an arbitrary set of job parameters.
Execution of a Job can be initiated only when there is no running execution context and the execution context stack is empty. A PendingJob is a request for the future execution of a Job. A PendingJob is an internal Record whose fields are specified in Table 25. Once execution of a Job is initiated, the Job always executes to completion. No other Job may be initiated until the currently running Job completes. However, the currently running Job or external events may cause the enqueuing of additional PendingJobs that may be initiated sometime after completion of the currently running Job.
Field Name | Value | Meaning |
---|---|---|
[[Job]] | The name of a Job abstract operation | This is the abstract operation that is performed when execution of this PendingJob is initiated. Jobs are abstract operations that use NextJob rather than Return to indicate that they have completed. |
[[Arguments]] | A List | The List of argument values that are to be passed to [[Job]] when it is activated. |
[[Realm]] | A Realm Record | The Realm for the initial execution context when this Pending Job is initiated. |
[[HostDefined]] | Any, default value is undefined. | Field reserved for use by host environments that need to associate additional information with a pending Job. |
A Job Queue is a FIFO queue of PendingJob records. Each Job Queue has a name and the full set of available Job Queues are defined by an ECMAScript implementation. Every ECMAScript implementation has at least the Job Queues defined in Table 26.
Name | Purpose |
---|---|
ScriptJobs | Jobs that validate and evaluate ECMAScript Script and Module source text. See clauses 10 and 15. |
PromiseJobs | Jobs that are responses to the settlement of a Promise (see 25.4). |
A request for the future execution of a Job is made by enqueueing, on a Job Queue, a PendingJob record that includes a Job abstract operation name and any necessary argument values. When there is no running execution context and the execution context stack is empty, the ECMAScript implementation removes the first PendingJob from a Job Queue and uses the information contained in it to create an execution context and starts execution of the associated Job abstract operation.
The PendingJob records from a single Job Queue are always initiated in FIFO order. This specification does not define the order in which multiple Job Queues are serviced. An ECMAScript implementation may interweave the FIFO evaluation of the PendingJob records of a Job Queue with the evaluation of the PendingJob records of one or more other Job Queues. An implementation must define what occurs when there are no running execution context and all Job Queues are empty.
NOTE Typically an ECMAScript implementation will have its Job Queues pre-initialized with at least one PendingJob and one of those Jobs will be the first to be executed. An implementation might choose to free all resources and terminate if the current Job completes and all Job Queues are empty. Alternatively, it might choose to wait for a some implementation specific agent or mechanism to enqueue new PendingJob requests.
The following abstract operations are used to create and manage Jobs and Job Queues:
The EnqueueJob abstract operation requires three arguments: queueName, job, and arguments. It performs the following steps:
An algorithm step such as:
is used in Job abstract operations in place of:
Job abstract operations must not contain a Return step or a ReturnIfAbrupt step. The NextJob result operation is equivalent to the following steps:
An ECMAScript implementation performs the following steps prior to the execution of any Jobs or the evaluation of any ECMAScript code:
"ScriptJobs"
, ScriptEvaluationJob, « sourceText »)."ScriptJobs"
, TopLevelModuleEvaluationJob, « sourceText
»).The abstract operation InitializeHostDefinedRealm with parameter realm performs the following steps:
All ordinary objects have an internal slot called [[Prototype]]. The value of this internal slot is either null or an object and is used for implementing inheritance. Data properties of the [[Prototype]] object are inherited (are visible as properties of the child object) for the purposes of get access, but not for set access. Accessor properties are inherited for both get access and set access.
Every ordinary object has a Boolean-valued [[Extensible]] internal slot that controls whether or not properties may be added to the object. If the value of the [[Extensible]] internal slot is false then additional properties may not be added to the object. In addition, if [[Extensible]] is false the value of the [[Prototype]] internal slot of the object may not be modified. Once the value of an object’s [[Extensible]] internal slot has been set to false it may not be subsequently changed to true.
In the following algorithm descriptions, assume O is an ordinary object, P is a property key value, V is any ECMAScript language value, and Desc is a Property Descriptor record.
When the [[GetPrototypeOf]] internal method of O is called the following steps are taken:
When the [[SetPrototypeOf]] internal method of O is called with argument V the following steps are taken:
NOTE The loop in step 8 guarantees that there will be no circularities in any prototype chain that only includes objects that use the ordinary object definitions for [[GetPrototypeOf]] and [[SetPrototypeOf]].
When the [[IsExtensible]] internal method of O is called the following steps are taken:
When the [[PreventExtensions]] internal method of O is called the following steps are taken:
When the [[GetOwnProperty]] internal method of O is called with property key P, the following steps are taken:
When the abstract operation OrdinaryGetOwnProperty is called with Object O and with property key P, the following steps are taken:
When the [[DefineOwnProperty]] internal method of O is called with property key P and Property Descriptor Desc, the following steps are taken:
When the abstract operation OrdinaryDefineOwnProperty is called with Object O, property key P, and Property Descriptor Desc the following steps are taken:
When the abstract operation IsCompatiblePropertyDescriptor is called with Boolean value Extensible, and Property Descriptors Desc, and Current the following steps are taken:
When the abstract operation ValidateAndApplyPropertyDescriptor is called with Object O, property key P, Boolean value extensible, and Property Descriptors Desc, and current the following steps are taken:
This algorithm contains steps that test various fields of the Property Descriptor Desc for specific values. The fields that are tested in this manner need not actually exist in Desc. If a field is absent then its value is considered to be false.
NOTE 1 If undefined is passed as the O argument only validation is performed and no object updates are performed.
NOTE 2 Step 8.b allows any field of Desc to be different from the corresponding field of current if current’s [[Configurable]] field is true. This even permits changing the [[Value]] of a property whose [[Writable]] attribute is false. This is allowed because a true [[Configurable]] attribute would permit an equivalent sequence of calls where [[Writable]] is first set to true, a new [[Value]] is set, and then [[Writable]] is set to false.
When the [[HasProperty]] internal method of O is called with property key P, the following steps are taken:
When the abstract operation OrdinaryHasProperty is called with Object O and with property key P, the following steps are taken:
When the [[Get]] internal method of O is called with property key P and ECMAScript language value Receiver the following steps are taken:
When the [[Set]] internal method of O is called with property key P, value V, and ECMAScript language value Receiver, the following steps are taken:
When the [[Delete]] internal method of O is called with property key P the following steps are taken:
When the [[Enumerate]] internal method of O is called the following steps are taken:
next
method iterates
over all the String-valued keys of enumerable properties of O. The Iterator object must inherit from
%IteratorPrototype% (25.1.2). The mechanics and order of enumerating the
properties is not specified but must conform to the rules specified below.The iterator’s next
method processes object properties to determine whether the property key should be returned as an iterator value. Returned property keys do not include keys
that are Symbols. Properties of the target object may be deleted during enumeration. A property that is deleted before it is
processed by the iterator’s next
method is ignored. If new properties are added to the target object
during enumeration, the newly added properties are not guaranteed to be processed in the active enumeration. A property name
will be returned by the iterator’s next
method at most once in any enumeration.
Enumerating the properties of the target object includes enumerating properties of its prototype, and the prototype of
the prototype, and so on, recursively; but a property of a prototype is not processed if it has the same name as a property
that has already been processed by the iterator’s next
method. The values of [[Enumerable]] attributes
are not considered when determining if a property of a prototype object has already been processed. The enumerable property
names of prototype objects must be obtained as if by invoking the prototype object’s [[Enumerate]] internal method.
[[Enumerate]] must obtain the own property keys of the target object as if by calling its [[OwnPropertyKeys]] internal
method. Property attributes of the target object must be obtained as if by calling its [[GetOwnProperty]] internal
method.
NOTE The following is an informative definition of an ECMAScript generator function that conforms to these rules:
function* enumerate(obj) {
let visited=new Set;
for (let key of Reflect.ownKeys(obj)) {
if (typeof key === "string") {
let desc = Reflect.getOwnPropertyDescriptor(obj,key);
if (desc) {
visited.add(key);
if (desc.enumerable) yield key;
}
}
}
let proto = Reflect.getPrototypeOf(obj)
if (proto === null) return;
for (let protoName of Reflect.enumerate(proto)) {
if (!visited.has(protoName)) yield protoName;
}
}
When the [[OwnPropertyKeys]] internal method of O is called the following steps are taken:
The abstract operation ObjectCreate with argument proto (an object or null) is used to specify the runtime creation of new ordinary objects. The optional argument internalSlotsList is a List of the names of additional internal slots that must be defined as part of the object. If the list is not provided, an empty List is used. This abstract operation performs the following steps:
The abstract operation OrdinaryCreateFromConstructor creates an ordinary object whose [[Prototype]]
value is retrieved from a constructor’s prototype
property, if it exists. Otherwise the intrinsic named
by intrinsicDefaultProto is used for [[Prototype]]. The optional internalSlotsList is a List of the names of additional internal slots that must be defined as
part of the object. If the list is not provided, an empty List is
used. This abstract operation performs the following steps:
The abstract operation GetPrototypeFromConstructor determines the [[Prototype]] value that should be
used to create an object corresponding to a specific constructor. The value is retrieved from the constructor’s
prototype
property, if it exists. Otherwise the intrinsic named by intrinsicDefaultProto is used for
[[Prototype]]. This abstract operation performs the following steps:
"prototype"
).NOTE If constructor does not supply a [[Prototype]] value, the default value that is used is obtained from the Code Realm of the constructor function rather than from the running execution context.
ECMAScript function objects encapsulate parameterized ECMAScript code closed over a lexical environment and support the dynamic evaluation of that code. An ECMAScript function object is an ordinary object and has the same internal slots and the same internal methods as other ordinary objects. The code of an ECMAScript function object may be either strict mode code (10.2.1) or non-strict mode code. An ECMAScript function object whose code is strict mode code is called a strict function. One whose code is not strict mode code is called a non-strict function.
ECMAScript function objects have the additional internal slots listed in Table 27.
Internal Slot | Type | Description |
---|---|---|
[[Environment]] | Lexical Environment | The Lexical Environment that the function was closed over. Used as the outer environment when evaluating the code of the function. |
[[FormalParameters]] | Parse Node | The root parse node of the source text that defines the function’s formal parameter list. |
[[FunctionKind]] | String | Either "normal" , "classConstructor" or "generator" . |
[[ECMAScriptCode]] | Parse Node | The root parse node of the source text that defines the function’s body. |
[[ConstructorKind]] | String | Either "base" or "derived" . |
[[Realm]] | Realm Record | The Code Realm in which the function was created and which provides any intrinsic objects that are accessed when evaluating the function. |
[[ThisMode]] | (lexical, strict, global) | Defines how this references are interpreted within the formal parameters and code body of the function. lexical means that this refers to the this value of a lexically enclosing function. strict means that the this value is used exactly as provided by an invocation of the function. global means that a this value of undefined is interpreted as a reference to the global object. |
[[Strict]] | Boolean | true if this is a strict mode function, false if this is not a strict mode function. |
[[HomeObject]] | Object | If the function uses super , this is the object whose [[GetPrototypeOf]] provides the object where super property lookups begin. |
All ECMAScript function objects have the [[Call]] internal method defined here. ECMAScript functions that are also constructors in addition have the [[Construct]] internal method. ECMAScript function objects whose code is not strict mode code have the [[GetOwnProperty]] internal method defined here.
The [[Call]] internal method for an ECMAScript function object F is called with parameters thisArgument and argumentsList, a List of ECMAScript language values. The following steps are taken:
"classConstructor"
, throw a TypeError exception.NOTE When calleeContext is removed from the execution context stack in step 8 it must not be destroyed if it is suspended and retained for later resumption by an accessible generator object.
When the abstract operation PrepareForOrdinaryCall is called with function object F and ECMAScript language value newTarget, the following steps are taken:
When the abstract operation OrdinaryCallBindThis is called with function object F, execution context calleeContext, and ECMAScript value thisArgument the following steps are taken:
"uninitialized"
.When the abstract operation OrdinaryCallEvaluateBody is called with function object F and List argumentsList the following steps are taken:
The [[Construct]] internal method for an ECMAScript Function object F is called with parameters argumentsList and newTarget. argumentsList is a possibly empty List of ECMAScript language values. The following steps are taken:
"base"
, then
"%ObjectPrototype%"
)."base"
, perform OrdinaryCallBindThis(F,
calleeContext, thisArgument)."base"
, return NormalCompletion(thisArgument).The abstract operation FunctionAllocate requires the two arguments functionPrototype and strict. It also accepts one optional argument, functionKind. FunctionAllocate performs the following steps:
"normal"
, "non-constructor"
or "generator"
."normal"
."non-constructor"
, then
"normal"
."generator"
, set the [[ConstructorKind]] internal slot of F to
"derived"
."base"
."derived"
constructors to prevent [[Construct]] from
preallocating a generator instance. Generator instance objects are allocated when EvaluateBody is applied to the
GeneratorBody of a generator function.The abstract operation FunctionInitialize requires the arguments: a function object F, kind which is one of (Normal, Method, Arrow), a parameter list production specified by ParameterList, a body production specified by Body, a Lexical Environment specified by Scope. FunctionInitialize performs the following steps:
length
own property."length"
,
PropertyDescriptor{[[Value]]: len, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
true}).The abstract operation FunctionCreate requires the arguments: kind which is one of (Normal, Method, Arrow), a parameter list production specified by ParameterList, a body production specified by Body, a Lexical Environment specified by Scope, a Boolean flag Strict, and optionally, an object prototype. FunctionCreate performs the following steps:
"non-constructor"
."normal"
.The abstract operation GeneratorFunctionCreate requires the arguments: kind which is one of (Normal, Method), a parameter list production specified by ParameterList, a body production specified by Body, a Lexical Environment specified by Scope, and a Boolean flag Strict. GeneratorFunctionCreate performs the following steps:
"generator"
).The abstract operation AddRestrictedFunctionProperties is called with a function object F and Realm Record realm as its argument. It performs the following steps:
"caller"
,
PropertyDescriptor {[[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]: false,
[[Configurable]]: true})."arguments"
,
PropertyDescriptor {[[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]: false,
[[Configurable]]: true}).The %ThrowTypeError% intrinsic is an anonymous built-in function object that is defined once for each Realm. When %ThrowTypeError% is called it performs the following steps:
The value of the [[Extensible]] internal slot of a %ThrowTypeError% function is false.
The length
property of a %ThrowTypeError% function has the attributes { [[Writable]]: false,
[[Enumerable]]: false, [[Configurable]]: false }.
The abstract operation MakeConstructor requires a Function argument F and optionally, a
Boolean writablePrototype and an object prototype. If prototype is provided it is assumed
to already contain, if needed, a "constructor"
property whose value is F. This operation converts
F into a constructor by performing the following steps:
prototype
own property."constructor"
, PropertyDescriptor{[[Value]]: F, [[Writable]]: writablePrototype,
[[Enumerable]]: false, [[Configurable]]: true })."prototype"
, PropertyDescriptor{[[Value]]: prototype, [[Writable]]: writablePrototype,
[[Enumerable]]: false, [[Configurable]]: false}).The abstract operation MakeClassConstructor with argument F performs the following steps:
"normal"
."classConstructor"
.The abstract operation MakeMethod with arguments F and homeObject configures F as a method by performing the following steps:
The abstract operation SetFunctionName requires a Function argument F, a String or Symbol
argument name and optionally a String argument prefix. This operation adds a name
property to F by performing the following steps:
name
own property."["
, description, and "]"
."name"
,
PropertyDescriptor{[[Value]]: name, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
true}).NOTE 1 When an execution context is established for evaluating an ECMAScript function a new function Environment Record is created and bindings for each formal parameter are instantiated in that Environment Record. Each declaration in the function body is also instantiated. If the function’s formal parameters do not include any default value initializers then the body declarations are instantiated in the same Environment Record as the parameters. If default value parameter initializers exist, a second Environment Record is created for the body declarations. Formal parameters and functions are initialized as part of FunctionDeclarationInstantiation. All other bindings are initialized during evaluation of the function body.
FunctionDeclarationInstantiation is performed as follows using arguments func and argumentsList. func is the function object for which the execution context is being established.
"arguments"
is an element of parameterNames, then
"arguments"
is an element of functionNames or if "arguments"
is an element of
lexicalNames, then
"arguments"
)."arguments"
)."arguments"
, ao)."arguments"
to parameterNames.eval
(see 12.3.4.1) can determine whether any var scoped
declarations introduced by the eval code conflict with pre-existing top-level lexically scoped declarations. This
is not needed for strict functions because a strict direct eval
always places all declarations into a
new Environment Record.NOTE 2 B.3.3 provides an extension to the above algorithm that is necessary for backwards compatibility with web browser implementations of ECMAScript that predate ECMAScript 2015.
The built-in function objects defined in this specification may be implemented as either ECMAScript function objects (9.2) whose behaviour is provided using ECMAScript code or as implementation provided exotic function objects whose behaviour is provided in some other manner. In either case, the effect of calling such functions must conform to their specifications. An implementation may also provide additional built-in function objects that are not defined in this specification.
If a built-in function object is implemented as an exotic object it must have the ordinary object behaviour specified in 9.1. All such exotic function objects also have [[Prototype]], [[Extensible]], and [[Realm]] internal slots.
Unless otherwise specified every built-in function object has the %FunctionPrototype% object (19.2.3) as the initial value of its [[Prototype]] internal slot.
The behaviour specified for each built-in function via algorithm steps or other means is the specification of the
function body behaviour for both [[Call]] and [[Construct]] invocations of the function. However, [[Construct]] invocation
is not supported by all built-in functions. For each built-in function, when invoked with [[Call]], the [[Call]]
thisArgument provides the this value, the [[Call]] argumentsList provides
the named parameters, and the NewTarget value is undefined. When invoked with [[Construct]], the
this value is uninitialized, the [[Construct]] argumentsList provides the named
parameters, and the [[Construct]] newTarget parameter provides the NewTarget value. If the built-in function is
implemented as an ECMAScript function object then this specified behaviour
must be implemented by the ECMAScript code that is the body of the function. Built-in functions that are ECMAScript function
objects must be strict mode functions. If a built-in constructor has any [[Call]] behaviour other than throwing a TypeError exception, an ECMAScript implementation of the function must be done in a manner that does
not cause the function’s [[FunctionKind]] internal slot
to have the value "classConstructor"
.
Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method
unless otherwise specified in the description of a particular function. When a built-in constructor is called as part of a
new
expression the argumentsList parameter of the invoked [[Construct]] internal method provides the
values for the built-in constructor’s named parameters.
Built-in functions that are not constructors do not have a prototype
property unless otherwise specified in
the description of a particular function.
If a built-in function object is not implemented as an ECMAScript function it must provide [[Call]] and [[Construct]] internal methods that conform to the following definitions:
The [[Call]] internal method for a built-in function object F is called with parameters thisArgument and argumentsList, a List of ECMAScript language values. The following steps are taken:
NOTE When calleeContext is removed from the execution context stack it must not be destroyed if it has been suspended and retained by an accessible generator object for later resumption.
The [[Construct]] internal method for built-in function object F is called with parameters argumentsList and newTarget. The steps performed are the same as [[Call]] (see 9.3.1) except that step 9 is replaced by:
9. Let result be the Completion Record that is the result of evaluating F in an implementation defined manner that conforms to the specification of F. The this value is uninitialized, argumentsList provides the named parameters, and newTarget provides the NewTarget value.
The abstract operation CreateBuiltinFunction takes arguments realm, prototype, and steps. The optional argument internalSlotsList is a List of the names of additional internal slots that must be defined as part of the object. If the list is not provided, an empty List is used. CreateBuiltinFunction returns a built-in function object created by the following steps:
Each built-in function defined in this specification is created as if by calling the CreateBuiltinFunction abstract operation, unless otherwise specified.
This specification defines several kinds of built-in exotic objects. These objects generally behave similar to ordinary objects except for a few specific situations. The following exotic objects use the ordinary object internal methods except where it is explicitly specified otherwise below:
A bound function is an exotic object that wraps another function object. A bound function is callable (it has a [[Call]] internal method and may have a [[Construct]] internal method). Calling a bound function generally results in a call of its wrapped function.
Bound function objects do not have the internal slots of ECMAScript function objects defined in Table 27. Instead they have the internal slots defined in Table 28.
Internal Slot | Type | Description |
---|---|---|
[[BoundTargetFunction]] | Callable Object | The wrapped function object. |
[[BoundThis]] | Any | The value that is always passed as the this value when calling the wrapped function. |
[[BoundArguments]] | List of Any | A list of values whose elements are used as the first arguments to any call to the wrapped function. |
Unlike ECMAScript function objects, bound function objects do not use an alternative definition of the [[GetOwnProperty]] internal methods. Bound function objects provide all of the essential internal methods as specified in 9.1. However, they use the following definitions for the essential internal methods of function objects.
When the [[Call]] internal method of an exotic bound function object, F, which was created using the bind function is called with parameters thisArgument and argumentsList, a List of ECMAScript language values, the following steps are taken:
When the [[Construct]] internal method of an exotic bound function object, F that was created using the bind function is called with a list of arguments argumentsList and newTarget, the following steps are taken:
The abstract operation BoundFunctionCreate with arguments targetFunction, boundThis and boundArgs is used to specify the creation of new Bound Function exotic objects. It performs the following steps:
An Array object is an exotic object that gives special treatment to array index property keys (see 6.1.7). A property whose property name is an array index is also called an element.
Every Array object has a length
property whose value is always a nonnegative integer less than 232. The value of the length
property is numerically
greater than the name of every own property whose name is an array index; whenever an own property of an Array object is
created or changed, other properties are adjusted as necessary to maintain this invariant. Specifically, whenever an own
property is added whose name is an array index, the value of the length
property is changed, if necessary, to
be one more than the numeric value of that array index; and whenever the value of the length
property is
changed, every own property whose name is an array index whose value is not smaller than the new length is deleted. This
constraint applies only to own properties of an Array object and is unaffected by length
or array index
properties that may be inherited from its prototypes.
NOTE A String property name P is an array index if and only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal to 232−1.
Array exotic objects always have a non-configurable property named "length"
.
Array exotic objects provide an alternative definition for the [[DefineOwnProperty]] internal method. Except for that internal method, Array exotic objects provide all of the other essential internal methods as specified in 9.1.
When the [[DefineOwnProperty]] internal method of an Array exotic object A is called with property key P, and Property Descriptor Desc the following steps are taken:
"length"
, then
"length"
)."length"
, oldLenDesc).The abstract operation ArrayCreate with argument length (a positive integer) and optional argument proto is used to specify the creation of new Array exotic objects. It performs the following steps:
"length"
,
PropertyDescriptor{[[Value]]: length, [[Writable]]: true, [[Enumerable]]: false,
[[Configurable]]: false}).The abstract operation ArraySpeciesCreate with arguments originalArray and length is used to specify the creation of a new Array object using a constructor function that is derived from originalArray. It performs the following steps:
"constructor"
).NOTE If originalArray was created using the standard built-in Array constructor for a Realm that is not the Realm of the running execution context, then a new Array is created using the Realm of the running execution context. This maintains compatibility with Web browsers that have historically had that behaviour for the Array.prototype methods that now are defined using ArraySpeciesCreate.
When the abstract operation ArraySetLength is called with an Array exotic object A, and Property Descriptor Desc the following steps are taken:
"length"
,
Desc)."length"
)."length"
,
newLenDesc)."length"
, newLenDesc)."length"
, newLenDesc)."length"
,
PropertyDescriptor{[[Writable]]: false}). This call will always return true.NOTE In steps 3 and 4, if Desc.[[Value]] is an object then its valueOf
method is called twice. This is legacy
behaviour that was specified with this effect starting with the 2nd Edition of this specification.
A String object is an exotic object that encapsulates a String value and exposes virtual integer indexed data
properties corresponding to the individual code unit elements of the String value. Exotic String objects always have a
data property named "length"
whose value is the number of code unit elements in the encapsulated String
value. Both the code unit data properties and the "length"
property are non-writable and
non-configurable.
Exotic String objects have the same internal slots as ordinary objects. They also have a [[StringData]] internal slot.
Exotic String objects provide alternative definitions for the following internal methods. All of the other exotic String object essential internal methods that are not defined below are as specified in 9.1.
When the [[GetOwnProperty]] internal method of an exotic String object S is called with property key P the following steps are taken:
When the abstract operation StringGetIndexProperty is called with an exotic String object S and with property key P, the following steps are taken:
When the [[HasProperty]] internal method of an exotic String object S is called with property key P, the following steps are taken:
When the [[OwnPropertyKeys]] internal method of a String exotic object O is called the following steps are taken:
The abstract operation StringCreate with arguments value and prototype is used to specify the creation of new exotic String objects. It performs the following steps:
"length"
,
PropertyDescriptor{[[Value]]: length, [[Writable]]: false, [[Enumerable]]: false,
[[Configurable]]: false }).Most ECMAScript functions make an arguments objects available to their code. Depending upon the characteristics of the function definition, its argument object is either an ordinary object or an arguments exotic object. An arguments exotic object is an exotic object whose array index properties map to the formal parameters bindings of an invocation of its associated ECMAScript function.
Arguments exotic objects have the same internal slots as ordinary objects. They also have a [[ParameterMap]] internal
slot. Ordinary arguments objects also have a [[ParameterMap]] internal slot whose value is always undefined. For ordinary
argument objects the [[ParameterMap]] internal slot is only used by Object.prototype.toString
(19.1.3.6) to identify them as such.
Arguments exotic objects provide alternative definitions for the following internal methods. All of the other exotic arguments object essential internal methods that are not defined below are as specified in 9.1
NOTE 1 For non-strict functions the integer indexed data properties of an arguments object whose numeric name values are less than the number of formal parameters of the corresponding function object initially share their values with the corresponding argument bindings in the function’s execution context. This means that changing the property changes the corresponding value of the argument binding and vice-versa. This correspondence is broken if such a property is deleted and then redefined or if the property is changed into an accessor property. For strict mode functions, the values of the arguments object’s properties are simply a copy of the arguments passed to the function and there is no dynamic linkage between the property values and the formal parameter values.
NOTE 2 The ParameterMap object and its property values are used as a device for specifying the arguments object correspondence to argument bindings. The ParameterMap object and the objects that are the values of its properties are not directly observable from ECMAScript code. An ECMAScript implementation does not need to actually create or use such objects to implement the specified semantics.
NOTE 3 Arguments objects for strict mode functions define non-configurable accessor
properties named "caller"
and "callee"
which throw a TypeError exception on access. The
"callee"
property has a more specific meaning for non-strict functions and a "caller"
property
has historically been provided as an implementation-defined extension by some ECMAScript implementations. The strict
mode definition of these properties exists to ensure that neither of them is defined in any other manner by conforming
ECMAScript implementations.
The [[GetOwnProperty]] internal method of an arguments exotic object when called with a property key P performs the following steps:
"caller"
and desc.[[Value]] is a strict mode Function object, throw a TypeError
exception.If an implementation does not provide a built-in caller
property for argument exotic objects then step 8
of this algorithm is must be skipped.
The [[DefineOwnProperty]] internal method of an arguments exotic object when called with a property key P and Property Descriptor Desc performs the following steps:
The [[Get]] internal method of an arguments exotic object when called with a property key P and ECMAScript language value Receiver performs the following steps:
The [[Set]] internal method of an arguments exotic object when called with property key P, value V, and ECMAScript language value Receiver performs the following steps:
The [[Delete]] internal method of an arguments exotic object when called with a property key P performs the following steps:
The abstract operation CreateUnmappedArgumentsObject called with an argument argumentsList performs the following steps:
"length"
,
PropertyDescriptor{[[Value]]: len, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]:
true})."caller"
,
PropertyDescriptor {[[Get]]: %ThrowTypeError%, [[Set]]: %ThrowTypeError%, [[Enumerable]]: false, [[Configurable]]:
false})."callee"
,
PropertyDescriptor {[[Get]]: %ThrowTypeError%, [[Set]]: %ThrowTypeError%, [[Enumerable]]: false, [[Configurable]]:
false}).The abstract operation CreateMappedArgumentsObject is called with object func, parsed grammar phrase formals, List argumentsList, and Environment Record env. The following steps are performed:
"length"
,
PropertyDescriptor{[[Value]]: len, [[Writable]]: true, [[Enumerable]]: false,
[[Configurable]]: true})."callee"
,
PropertyDescriptor {[[Value]]: func, [[Writable]]: true, [[Enumerable]]: false,
[[Configurable]]: true}).The abstract operation MakeArgGetter called with String name and Environment Record env creates a built-in function object that when executed returns the value bound for name in env. It performs the following steps:
An ArgGetter function is an anonymous built-in function with [[name]] and [[env]] internal slots. When an ArgGetter function f that expects no arguments is called it performs the following steps:
NOTE ArgGetter functions are never directly accessible to ECMAScript code.
The abstract operation MakeArgSetter called with String name and Environment Record env creates a built-in function object that when executed sets the value bound for name in env. It performs the following steps:
An ArgSetter function is an anonymous built-in function with [[name]] and [[env]] internal slots. When an ArgSetter function f is called with argument value it performs the following steps:
NOTE ArgSetter functions are never directly accessible to ECMAScript code.
An Integer Indexed object is an exotic object that performs special handling of integer index property keys.
Integer Indexed exotic objects have the same internal slots as ordinary objects additionally [[ViewedArrayBuffer]], [[ArrayLength]], [[ByteOffset]], and [[TypedArrayName]] internal slots.
Integer Indexed Exotic objects provide alternative definitions for the following internal methods. All of the other Integer Indexed exotic object essential internal methods that are not defined below are as specified in 9.1.
When the [[GetOwnProperty]] internal method of an Integer Indexed exotic object O is called with property key P the following steps are taken:
When the [[HasProperty]] internal method of an Integer Indexed exotic object O is called with property key P, the following steps are taken:
When the [[DefineOwnProperty]] internal method of an Integer Indexed exotic object O is called with property key P, and Property Descriptor Desc the following steps are taken:
When the [[Get]] internal method of an Integer Indexed exotic object O is called with property key P and ECMAScript language value Receiver the following steps are taken:
When the [[Set]] internal method of an Integer Indexed exotic object O is called with property key P, value V, and ECMAScript language value Receiver, the following steps are taken:
When the [[OwnPropertyKeys]] internal method of an Integer Indexed exotic object O is called the following steps are taken:
The abstract operation IntegerIndexedObjectCreate with arguments prototype and internalSlotsList is used to specify the creation of new Integer Indexed exotic objects. The argument internalSlotsList is a List of the names of additional internal slots that must be defined as part of the object. IntegerIndexedObjectCreate performs the following steps:
The abstract operation IntegerIndexedElementGet with arguments O and index performs the following steps:
The abstract operation IntegerIndexedElementSet with arguments O, index, and value performs the following steps:
A module namespace object is an exotic object that exposes the bindings exported from an ECMAScript Module (See 15.2.3). There is a one-to-one correspondence between
the String-keyed own properties of a module namespace exotic object and the binding names exported by the Module. The exported bindings include any bindings that are indirectly exported using export
*
export items. Each String-valued own property key is the StringValue of the
corresponding exported binding name. These are the only String-keyed properties of a module namespace exotic object. Each
such property has the attributes {[[Configurable]]: false, [[Enumerable]]: true}. Module namespace objects are not extensible.
Module namespace objects have the internal slots defined in Table 29.
Internal Slot | Type | Description |
---|---|---|
[[Module]] | Module Record | The Module Record whose exports this namespace exposes. |
[[Exports]] | List of String | A List containing the String values of the exported names exposed as own properties of this object. The list is ordered as if an Array of those String values had been sorted using Array.prototype.sort using SortCompare as comparefn. |
Module namespace exotic objects provide alternative definitions for all of the internal methods.
When the [[GetPrototypeOf]] internal method of a module namespace exotic object O is called the following steps are taken:
When the [[SetPrototypeOf]] internal method of a module namespace exotic object O is called with argument V the following steps are taken:
When the [[IsExtensible]] internal method of a module namespace exotic object O is called the following steps are taken:
When the [[PreventExtensions]] internal method of a module namespace exotic object O is called the following steps are taken:
When the [[GetOwnProperty]] internal method of a module namespace exotic object O is called with property key P, the following steps are taken:
When the [[DefineOwnProperty]] internal method of a module namespace exotic object O is called with property key P and Property Descriptor Desc, the following steps are taken:
When the [[HasProperty]] internal method of a module namespace exotic object O is called with property key P, the following steps are taken:
When the [[Get]] internal method of a module namespace exotic object O is called with property key P and ECMAScript language value Receiver the following steps are taken:
"ambiguous"
.NOTE ResolveExport is idempotent and side-effect free. An implementation might choose to pre-compute or cache the ResolveExport results for the [[Exports]] of each module namespace exotic object.
When the [[Set]] internal method of a module namespace exotic object O is called with property key P, value V, and ECMAScript language value Receiver, the following steps are taken:
When the [[Delete]] internal method of a module namespace exotic object O is called with property key P the following steps are taken:
When the [[Enumerate]] internal method of a module namespace exotic object O is called the following steps are taken:
When the [[OwnPropertyKeys]] internal method of a module namespace exotic object O is called the following steps are taken:
The abstract operation ModuleNamespaceCreate with arguments module, and exports is used to specify the creation of new module namespace exotic objects. It performs the following steps:
A proxy object is an exotic object whose essential internal methods are partially implemented using ECMAScript code. Every proxy objects has an internal slot called [[ProxyHandler]]. The value of [[ProxyHandler]] is an object, called the proxy’s handler object, or null. Methods (see Table 30) of a handler object may be used to augment the implementation for one or more of the proxy object’s internal methods. Every proxy object also has an internal slot called [[ProxyTarget]] whose value is either an object or the null value. This object is called the proxy’s target object.
Internal Method | Handler Method |
---|---|
[[GetPrototypeOf]] | getPrototypeOf |
[[SetPrototypeOf]] | setPrototypeOf |
[[IsExtensible]] | isExtensible |
[[PreventExtensions]] | preventExtensions |
[[GetOwnProperty]] | getOwnPropertyDescriptor |
[[HasProperty]] | has |
[[Get]] | get |
[[Set]] | set |
[[Delete]] | deleteProperty |
[[DefineOwnProperty]] | defineProperty |
[[Enumerate]] | enumerate |
[[OwnPropertyKeys]] | ownKeys |
[[Call]] | apply |
[[Construct]] | construct |
When a handler method is called to provide the implementation of a proxy object internal method, the handler method is passed the proxy’s target object as a parameter. A proxy’s handler object does not necessarily have a method corresponding to every essential internal method. Invoking an internal method on the proxy results in the invocation of the corresponding internal method on the proxy’s target object if the handler object does not have a method corresponding to the internal trap.
The [[ProxyHandler]] and [[ProxyTarget]] internal slots of a proxy object are always initialized when the object is created and typically may not be modified. Some proxy objects are created in a manner that permits them to be subsequently revoked. When a proxy is revoked, its [[ProxyHander]] and [[ProxyTarget]] internal slots are set to null causing subsequent invocations of internal methods on that proxy object to throw a TypeError exception.
Because proxy objects permit the implementation of internal methods to be provided by arbitrary ECMAScript code, it is possible to define a proxy object whose handler methods violates the invariants defined in 6.1.7.3. Some of the internal method invariants defined in 6.1.7.3 are essential integrity invariants. These invariants are explicitly enforced by the proxy object internal methods specified in this section. An ECMAScript implementation must be robust in the presence of all possible invariant violations.
In the following algorithm descriptions, assume O is an ECMAScript proxy object, P is a property key value, V is any ECMAScript language value and Desc is a Property Descriptor record.
When the [[GetPrototypeOf]] internal method of a Proxy exotic object O is called the following steps are taken:
"getPrototypeOf"
).NOTE [[GetPrototypeOf]] for proxy objects enforces the following invariant:
The result of [[GetPrototypeOf]] must be either an Object or null.
If the target object is not extensible, [[GetPrototypeOf]] applied to the proxy object must return the same value as [[GetPrototypeOf]] applied to the proxy object’s target object.
When the [[SetPrototypeOf]] internal method of a Proxy exotic object O is called with argument V the following steps are taken:
"setPrototypeOf"
).NOTE [[SetPrototypeOf]] for proxy objects enforces the following invariant:
The result of [[SetPrototypeOf]] is a Boolean value.
If the target object is not extensible, the argument value must be the same as the result of [[GetPrototypeOf]] applied to target object.
When the [[IsExtensible]] internal method of a Proxy exotic object O is called the following steps are taken:
"isExtensible"
).NOTE [[IsExtensible]] for proxy objects enforces the following invariant:
The result of [[IsExtensible]] is a Boolean value.
[[IsExtensible]] applied to the proxy object must return the same value as [[IsExtensible]] applied to the proxy object’s target object with the same argument.
When the [[PreventExtensions]] internal method of a Proxy exotic object O is called the following steps are taken:
"preventExtensions"
).NOTE [[PreventExtensions]] for proxy objects enforces the following invariant:
The result of [[PreventExtensions]] is a Boolean value.
[[PreventExtensions]] applied to the proxy object only returns true if [[IsExtensible]] applied to the proxy object’s target object is false.
When the [[GetOwnProperty]] internal method of a Proxy exotic object O is called with property key P, the following steps are taken:
"getOwnPropertyDescriptor"
).NOTE [[GetOwnProperty]] for proxy objects enforces the following invariants:
The result of [[GetOwnProperty]] must be either an Object or undefined.
A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
A property cannot be reported as non-existent, if it exists as an own property of the target object and the target object is not extensible.
A property cannot be reported as existent, if it does not exists as an own property of the target object and the target object is not extensible.
A property cannot be reported as non-configurable, if it does not exists as an own property of the target object or if it exists as a configurable own property of the target object.
When the [[DefineOwnProperty]] internal method of a Proxy exotic object O is called with property key P and Property Descriptor Desc, the following steps are taken:
"defineProperty"
).NOTE [[DefineOwnProperty]] for proxy objects enforces the following invariants:
The result of [[DefineOwnProperty]] is a Boolean value.
A property cannot be added, if the target object is not extensible.
A property cannot be non-configurable, unless there exists a corresponding non-configurable own property of the target object.
If a property has a corresponding target object property then applying the Property Descriptor of the property to the target object using [[DefineOwnProperty]] will not throw an exception.
When the [[HasProperty]] internal method of a Proxy exotic object O is called with property key P, the following steps are taken:
"has"
).NOTE [[HasProperty]] for proxy objects enforces the following invariants:
The result of [[HasProperty]] is a Boolean value.
A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
A property cannot be reported as non-existent, if it exists as an own property of the target object and the target object is not extensible.
When the [[Get]] internal method of a Proxy exotic object O is called with property key P and ECMAScript language value Receiver the following steps are taken:
"get"
).NOTE [[Get]] for proxy objects enforces the following invariants:
The value reported for a property must be the same as the value of the corresponding target object property if the target object property is a non-writable, non-configurable own data property.
The value reported for a property must be undefined if the corresponding target object property is a non-configurable own accessor property that has undefined as its [[Get]] attribute.
When the [[Set]] internal method of a Proxy exotic object O is called with property key P, value V, and ECMAScript language value Receiver, the following steps are taken:
"set"
).NOTE [[Set]] for proxy objects enforces the following invariants:
The result of [[Set]] is a Boolean value.
Cannot change the value of a property to be different from the value of the corresponding target object property if the corresponding target object property is a non-writable, non-configurable own data property.
Cannot set the value of a property if the corresponding target object property is a non-configurable own accessor property that has undefined as its [[Set]] attribute.
When the [[Delete]] internal method of a Proxy exotic object O is called with property key P the following steps are taken:
"deleteProperty"
).NOTE [[Delete]] for proxy objects enforces the following invariant:
When the [[Enumerate]] internal method of a Proxy exotic object O is called the following steps are taken:
"enumerate"
).NOTE [[Enumerate]] for proxy objects enforces the following invariants:
When the [[OwnPropertyKeys]] internal method of a Proxy exotic object O is called the following steps are taken:
"ownKeys"
).NOTE [[OwnPropertyKeys]] for proxy objects enforces the following invariants:
The result of [[OwnPropertyKeys]] is a List.
The Type of each result List element is either String or Symbol.
The result List must contain the keys of all non-configurable own properties of the target object.
If the target object is not extensible, then the result List must contain all the keys of the own properties of the target object and no other values.
The [[Call]] internal method of a Proxy exotic object O is called with parameters thisArgument and argumentsList, a List of ECMAScript language values. The following steps are taken:
"apply"
).NOTE A Proxy exotic object only has a [[Call]] internal method if the initial value of its [[ProxyTarget]] internal slot is an object that has a [[Call]] internal method.
The [[Construct]] internal method of a Proxy exotic object O is called with parameters argumentsList which is a possibly empty List of ECMAScript language values and newTarget. The following steps are taken:
"construct"
).NOTE 1 A Proxy exotic object only has a [[Construct]] internal method if the initial value of its [[ProxyTarget]] internal slot is an object that has a [[Construct]] internal method.
NOTE 2 [[Construct]] for proxy objects enforces the following invariants:
The abstract operation ProxyCreate with arguments target and handler is used to specify the creation of new Proxy exotic objects. It performs the following steps:
ECMAScript code is expressed using Unicode, version 5.1 or later. ECMAScript source text is a sequence of code points. All Unicode code point values from U+0000 to U+10FFFF, including surrogate code points, may occur in source text where permitted by the ECMAScript grammars. The actual encodings used to store and interchange ECMAScript source text is not relevant to this specification. Regardless of the external source text encoding, a conforming ECMAScript implementation processes the source text as if it was an equivalent sequence of SourceCharacter values. Each SourceCharacter being a Unicode code point. Conforming ECMAScript implementations are not required to perform any normalization of source text, or behave as though they were performing normalization of source text.
The components of a combining character sequence are treated as individual Unicode code points even though a user might think of the whole sequence as a single character.
NOTE In string literals, regular expression literals, template literals and identifiers, any Unicode code point may also be expressed using Unicode escape sequences that explicitly express a code point’s numeric value. Within a comment, such an escape sequence is effectively ignored as part of the comment.
ECMAScript differs from the Java programming language in the behaviour of Unicode escape sequences. In a Java program,
if the Unicode escape sequence \u000A
, for example, occurs within a single-line comment, it is interpreted as
a line terminator (Unicode code point U+000A is LINE FEED (LF) and therefore the next code point is not part of the
comment. Similarly, if the Unicode escape sequence \u000A
occurs within a string literal in a Java program,
it is likewise interpreted as a line terminator, which is not allowed within a string literal—one must write
\n
instead of \u000A
to cause a LINE FEED (LF) to be part of the String value of a string
literal. In an ECMAScript program, a Unicode escape sequence occurring within a comment is never interpreted and therefore
cannot contribute to termination of the comment. Similarly, a Unicode escape sequence occurring within a string literal in
an ECMAScript program always contributes to the literal and is never interpreted as a line terminator or as a code point
that might terminate the string literal.
The UTF16Encoding of a numeric code point value, cp, is determined as follows:
Two code units, lead and trail, that form a UTF-16 surrogate pair are converted to a code point by performing the following steps:
There are four types of ECMAScript code:
Global code is source text that is treated as an ECMAScript Script. The global code of a particular Script does not include any source text that is parsed as part of a FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, MethodDefinition, ArrowFunction, ClassDeclaration, or ClassExpression.
Eval code is the source text supplied to the built-in eval
function. More precisely, if the
parameter to the built-in eval
function is a String, it is treated as an ECMAScript Script. The eval
code for a particular invocation of eval
is the global code portion of that Script.
Function code is source text that is parsed to supply the value of the [[ECMAScriptCode]] and [[FormalParameters]] internal slots (see 9.2) of an ECMAScript function object. The function code of a particular ECMAScript function does not include any source text that is parsed as the function code of a nested FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, MethodDefinition, ArrowFunction, ClassDeclaration, or ClassExpression.
Module code is source text that is code that is provided as a ModuleBody. It is the code that is directly evaluated when a module is initialized. The module code of a particular module does not include any source text that is parsed as part of a nested FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, MethodDefinition, ArrowFunction, ClassDeclaration, or ClassExpression.
NOTE Function code is generally provided as the bodies of Function Definitions (14.1), Arrow Function Definitions (14.2), Method Definitions (14.3) and
Generator Definitions (14.4). Function code is also derived from the
arguments to the Function
constructor (19.2.1.1) and the
GeneratorFunction constructor (25.2.1.1).
An ECMAScript Script syntactic unit may be processed using either unrestricted or strict mode syntax and semantics. Code is interpreted as strict mode code in the following situations:
Global code is strict mode code if it begins with a Directive Prologue that contains a Use Strict Directive (see 14.1.1).
Module code is always strict mode code.
All parts of a ClassDeclaration or a ClassExpression are strict mode code.
Eval code is strict mode code if it begins with a Directive Prologue that contains a Use Strict Directive or if the call to eval is a direct eval (see 12.3.4.1) that is contained in strict mode code.
Function code is strict mode code if the associated FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, MethodDefinition, or ArrowFunction is contained in strict mode code or if the code that produces the value of the function’s [[ECMAScriptCode]] internal slot begins with a Directive Prologue that contains a Use Strict Directive.
Function code that is supplied as the arguments to the built-in Function
and Generator
constructors is strict mode code if the last argument is a String that when processed is a FunctionBody that begins with a Directive Prologue that contains a Use Strict Directive.
ECMAScript code that is not strict mode code is called non-strict code.
An ECMAScript implementation may support the evaluation of exotic function objects whose evaluative behaviour is expressed in some implementation defined form of executable code other than via ECMAScript code. Whether a function object is an ECMAScript code function or a non-ECMAScript function is not semantically observable from the perspective of an ECMAScript code function that calls or is called by such a non-ECMAScript function.
The source text of an ECMAScript Script or Module is first converted into a sequence of input elements, which are tokens, line terminators, comments, or white space. The source text is scanned from left to right, repeatedly taking the longest possible sequence of code points as the next input element.
There are several situations where the identification of lexical input elements is sensitive to the syntactic grammar context that is consuming the input elements. This requires multiple goal symbols for the lexical grammar. The InputElementRegExpOrTemplateTail goal is used in syntactic grammar contexts where a RegularExpressionLiteral, a TemplateMiddle, or a TemplateTail is permitted. The InputElementRegExp goal symbol is used in all syntactic grammar contexts where a RegularExpressionLiteral is permitted but neither a TemplateMiddle, nor a TemplateTail is permitted. The InputElementTemplateTail goal is used in all syntactic grammar contexts where a TemplateMiddle or a TemplateTail is permitted but a RegularExpressionLiteral is not permitted. In all other contexts, InputElementDiv is used as the lexical goal symbol.
NOTE The use of multiple lexical goals ensures that there are no lexical ambiguities that would affect automatic semicolon insertion. For example, there are no syntactic grammar contexts where both a leading division or division-assignment, and a leading RegularExpressionLiteral are permitted. This is not affected by semicolon insertion (see 11.9); in examples such as the following:
a = b
/hi/g.exec(c).map(d);
where the first non-whitespace, non-comment code point after a LineTerminator is U+002F (SOLIDUS) and the syntactic context allows division or division-assignment, no semicolon is inserted at the LineTerminator. That is, the above example is interpreted in the same way as:
a = b / hi / g.exec(c).map(d);
The Unicode format-control characters (i.e., the characters in category “Cf” in the Unicode Character Database such as LEFT-TO-RIGHT MARK or RIGHT-TO-LEFT MARK) are control codes used to control the formatting of a range of text in the absence of higher-level protocols for this (such as mark-up languages).
It is useful to allow format-control characters in source text to facilitate editing and display. All format control characters may be used within comments, and within string literals, template literals, and regular expression literals.
U+200C (ZERO WIDTH NON-JOINER) and U+200D (ZERO WIDTH JOINER) are format-control characters that are used to make necessary distinctions when forming words or phrases in certain languages. In ECMAScript source text these code points may also be used in an IdentifierName (see 11.6.1) after the first character.
U+FEFF (ZERO WIDTH NO-BREAK SPACE) is a format-control character used primarily at the start of a text to mark it as Unicode and to allow detection of the text's encoding and byte order. <ZWNBSP> characters intended for this purpose can sometimes also appear after the start of a text, for example as a result of concatenating files. In ECMAScript source text <ZWNBSP> code points are treated as white space characters (see 11.2).
The special treatment of certain format-control characters outside of comments, string literals, and regular expression literals is summarized in Table 31.
Code Point | Name | Abbreviation | Usage |
---|---|---|---|
U+200C |
ZERO WIDTH NON-JOINER | <ZWNJ> | IdentifierPart |
U+200D |
ZERO WIDTH JOINER | <ZWJ> | IdentifierPart |
U+FEFF |
ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> | WhiteSpace |
White space code points are used to improve source text readability and to separate tokens (indivisible lexical units) from each other, but are otherwise insignificant. White space code points may occur between any two tokens and at the start or end of input. White space code points may occur within a StringLiteral, a RegularExpressionLiteral, a Template, or a TemplateSubstitutionTail where they are considered significant code points forming part of a literal value. They may also occur within a Comment, but cannot appear within any other kind of token.
The ECMAScript white space code points are listed in Table 32.
Code Point | Name | Abbreviation |
---|---|---|
U+0009 |
CHARACTER TABULATION | <TAB> |
U+000B |
LINE TABULATION | <VT> |
U+000C |
FORM FEED (FF) | <FF> |
U+0020 |
SPACE | <SP> |
U+00A0 |
NO-BREAK SPACE | <NBSP> |
U+FEFF |
ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> |
Other category “Zs” | Any other Unicode “Separator, space” code point | <USP> |
ECMAScript implementations must recognize as WhiteSpace code points listed in the “Separator, space” (Zs) category by Unicode 5.1. ECMAScript implementations may also recognize as WhiteSpace additional category Zs code points from subsequent editions of the Unicode Standard.
NOTE Other than for the code points listed in Table 32, ECMAScript WhiteSpace intentionally excludes all code points that have the Unicode “White_Space” property but which are not classified in category “Zs”.
Like white space code points, line terminator code points are used to improve source text readability and to separate tokens (indivisible lexical units) from each other. However, unlike white space code points, line terminators have some influence over the behaviour of the syntactic grammar. In general, line terminators may occur between any two tokens, but there are a few places where they are forbidden by the syntactic grammar. Line terminators also affect the process of automatic semicolon insertion (11.9). A line terminator cannot occur within any token except a StringLiteral, Template, or TemplateSubstitutionTail. Line terminators may only occur within a StringLiteral token as part of a LineContinuation.
A line terminator can occur within a MultiLineComment (11.4) but cannot occur within a SingleLineComment.
Line terminators are included in the set of white space code points that are matched by the \s
class in
regular expressions.
The ECMAScript line terminator code points are listed in Table 33.
Code Point | Unicode Name | Abbreviation |
---|---|---|
U+000A |
LINE FEED (LF) | <LF> |
U+000D |
CARRIAGE RETURN (CR) | <CR> |
U+2028 |
LINE SEPARATOR | <LS> |
U+2029 |
PARAGRAPH SEPARATOR | <PS> |
Only the Unicode code points in Table 33 are treated as line terminators. Other new line or line breaking Unicode code points are not treated as line terminators but are treated as white space if they meet the requirements listed in Table 32. The sequence <CR><LF> is commonly used as a line terminator. It should be considered a single SourceCharacter for the purpose of reporting line numbers.
Comments can be either single or multi-line. Multi-line comments cannot nest.
Because a single-line comment can contain any Unicode code point except a LineTerminator code
point, and because of the general rule that a token is always as long as possible, a single-line comment always consists of
all code points from the //
marker to the end of the line. However, the LineTerminator at
the end of the line is not considered to be part of the single-line comment; it is recognized separately by the lexical
grammar and becomes part of the stream of input elements for the syntactic grammar. This point is very important, because it
implies that the presence or absence of single-line comments does not affect the process of automatic semicolon insertion (see
11.9).
Comments behave like white space and are discarded except that, if a MultiLineComment contains a line terminator code point, then the entire comment is considered to be a LineTerminator for purposes of parsing by the syntactic grammar.
/*
MultiLineCommentCharsopt */
*
PostAsteriskCommentCharsopt*
PostAsteriskCommentCharsopt*
/
or *
//
SingleLineCommentCharsoptNOTE The DivPunctuator, RegularExpressionLiteral, RightBracePunctuator, and TemplateSubstitutionTail productions derive additional tokens that are not included in the CommonToken production.
IdentifierName and ReservedWord are tokens that are interpreted according to the Default Identifier Syntax given in Unicode Standard Annex #31, Identifier and Pattern Syntax, with some small modifications. ReservedWord is an enumerated subset of IdentifierName. The syntactic grammar defines Identifier as an IdentifierName that is not a ReservedWord (see 11.6.2). The Unicode identifier grammar is based on character properties specified by the Unicode Standard. The Unicode code points in the specified categories in version 5.1.0 of the Unicode standard must be treated as in those categories by all conforming ECMAScript implementations. ECMAScript implementations may recognize identifier code points defined in later editions of the Unicode Standard.
NOTE 1 This standard specifies specific code point additions: U+0024 (DOLLAR SIGN) and U+005F (LOW LINE) are permitted anywhere in an IdentifierName, and the code points U+200C (ZERO WIDTH NON-JOINER) and U+200D (ZERO WIDTH JOINER) are permitted anywhere after the first code point of an IdentifierName.
Unicode escape sequences are permitted in an IdentifierName, where they contribute a single
Unicode code point to the IdentifierName. The code point is expressed by the HexDigits of the UnicodeEscapeSequence (see 11.8.4). The \
preceding the UnicodeEscapeSequence and the u
and { }
code units, if they appear, do not
contribute code points to the IdentifierName. A UnicodeEscapeSequence cannot
be used to put a code point into an IdentifierName that would otherwise be illegal. In other words,
if a \
UnicodeEscapeSequence sequence were replaced by the SourceCharacter it contributes, the result must still be a valid IdentifierName
that has the exact same sequence of SourceCharacter elements as the original IdentifierName. All interpretations of IdentifierName within this specification
are based upon their actual code points regardless of whether or not an escape sequence was used to contribute any
particular code point.
Two IdentifierName that are canonically equivalent according to the Unicode standard are not equal unless, after replacement of each UnicodeEscapeSequence, they are represented by the exact same sequence of code points.
$
_
\
UnicodeEscapeSequence$
_
\
UnicodeEscapeSequenceThe definitions of the nonterminal UnicodeEscapeSequence is given in 11.8.4.
NOTE 2 The sets of code points with Unicode properties “ID_Start” and “ID_Continue” include, respectively, the code points with Unicode properties “Other_ID_Start” and “Other_ID_Continue”.
\
UnicodeEscapeSequenceIt is a Syntax Error if SV(UnicodeEscapeSequence) is none
of "$"
, or "_"
, or the UTF16Encoding (10.1.1) of a code point matched by the UnicodeIDStart lexical
grammar production.
\
UnicodeEscapeSequenceIt is a Syntax Error if SV(UnicodeEscapeSequence) is none
of "$"
, or "_"
, or the UTF16Encoding (10.1.1) of either <ZWNJ> or <ZWJ>, or the UTF16Encoding of a Unicode code point that would be matched by the UnicodeIDContinue lexical grammar production.
\
UnicodeEscapeSequence are first replaced with the
code point represented by the UnicodeEscapeSequence and then the code points of the entire
IdentifierName are converted to code units by UTF16Encoding (10.1.1) each code point.A reserved word is an IdentifierName that cannot be used as an Identifier.
NOTE The ReservedWord definitions are specified as literal sequences
of specific SourceCharacter elements. A code point in a ReservedWord
cannot be expressed by a \
UnicodeEscapeSequence.
The following tokens are ECMAScript keywords and may not be used as Identifiers in ECMAScript programs.
break |
do |
in |
typeof |
case |
else |
instanceof |
var |
catch |
export |
new |
void |
class |
extends |
return |
while |
const |
finally |
super |
with |
continue |
for |
switch |
yield |
debugger |
function |
this |
|
default |
if |
throw |
|
delete |
import |
try |
The following tokens are reserved for used as keywords in future language extensions.
enum
await
await
is only treated as a FutureReservedWord when Module
is the goal symbol of the syntactic grammar.
NOTE Use of the following tokens within strict mode code (see 10.2.1) is also reserved. That usage is restricted using static semantic restrictions (see 12.1.1) rather than the lexical grammar:
implements |
package |
protected |
|
interface |
private |
public |
{ |
( |
) |
[ |
] |
. |
... |
; |
, |
< |
> |
<= |
>= |
== |
!= |
=== |
!== |
|
+ |
- |
* |
% |
++ |
-- |
<< |
>> |
>>> |
& |
| |
^ |
! |
~ |
&& |
|| |
? |
: |
= |
+= |
-= |
*= |
%= |
<<= |
>>= |
>>>= |
&= |
|= |
^= |
=> |
/
/=
}
null
true
false
.
DecimalDigitsopt ExponentPartopt.
DecimalDigits ExponentPartopt0
0
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
e
E
+
DecimalDigits-
DecimalDigits0b
BinaryDigits0B
BinaryDigits0
1
0o
OctalDigits0O
OctalDigits0
1
2
3
4
5
6
7
0x
HexDigits0X
HexDigits0
1
2
3
4
5
6
7
8
9
a
b
c
d
e
f
A
B
C
D
E
F
The SourceCharacter immediately following a NumericLiteral must not be an IdentifierStart or DecimalDigit.
NOTE For example:
3in
is an
error and not the two input elements 3
and in
.
A conforming implementation, when processing strict mode code (see 10.2.1), must not extend, as described in B.1.1, the syntax of NumericLiteral to include LegacyOctalIntegerLiteral, nor extend the syntax of DecimalIntegerLiteral to include NonOctalDecimalIntegerLiteral.
A numeric literal stands for a value of the Number type. This value is determined in two steps: first, a mathematical value (MV) is derived from the literal; second, this mathematical value is rounded as described below.
The MV of NumericLiteral :: DecimalLiteral is the MV of DecimalLiteral.
The MV of NumericLiteral :: BinaryIntegerLiteral is the MV of BinaryIntegerLiteral.
The MV of NumericLiteral :: OctalIntegerLiteral is the MV of OctalIntegerLiteral.
The MV of NumericLiteral :: HexIntegerLiteral is the MV of HexIntegerLiteral.
The MV of DecimalLiteral :: DecimalIntegerLiteral .
is the MV of DecimalIntegerLiteral.
The MV of DecimalLiteral :: DecimalIntegerLiteral .
DecimalDigits is the
MV of DecimalIntegerLiteral plus (the MV of DecimalDigits × 10–n), where
n is the number of code points in DecimalDigits.
The MV of DecimalLiteral :: DecimalIntegerLiteral .
ExponentPart is the MV
of DecimalIntegerLiteral × 10e, where e is the MV of ExponentPart.
The MV of DecimalLiteral :: DecimalIntegerLiteral .
DecimalDigits ExponentPart is (the MV of DecimalIntegerLiteral plus (the MV of DecimalDigits
× 10–n)) × 10e, where n is the number of code points in
DecimalDigits and e is the MV of ExponentPart.
The MV of DecimalLiteral :: .
DecimalDigits is the MV of DecimalDigits ×
10–n, where n is the number of code points in DecimalDigits.
The MV of DecimalLiteral :: .
DecimalDigits ExponentPart is the MV of
DecimalDigits × 10e–n, where n is the number of code points in
DecimalDigits and e is the MV of ExponentPart.
The MV of DecimalLiteral :: DecimalIntegerLiteral is the MV of DecimalIntegerLiteral.
The MV of DecimalLiteral :: DecimalIntegerLiteral ExponentPart is the MV of DecimalIntegerLiteral × 10e, where e is the MV of ExponentPart.
The MV of DecimalIntegerLiteral :: 0
is 0.
The MV of DecimalIntegerLiteral :: NonZeroDigit is the MV of NonZeroDigit.
The MV of DecimalIntegerLiteral :: NonZeroDigit DecimalDigits is (the MV of NonZeroDigit × 10n) plus the MV of DecimalDigits, where n is the number of code points in DecimalDigits.
The MV of DecimalDigits :: DecimalDigit is the MV of DecimalDigit.
The MV of DecimalDigits :: DecimalDigits DecimalDigit is (the MV of DecimalDigits × 10) plus the MV of DecimalDigit.
The MV of ExponentPart :: ExponentIndicator SignedInteger is the MV of SignedInteger.
The MV of SignedInteger :: DecimalDigits is the MV of DecimalDigits.
The MV of SignedInteger :: +
DecimalDigits is the MV of DecimalDigits.
The MV of SignedInteger :: -
DecimalDigits is the negative of the MV of DecimalDigits.
The MV of DecimalDigit :: 0
or of HexDigit :: 0
or of OctalDigit ::
0
or of BinaryDigit :: 0
is 0.
The MV of DecimalDigit :: 1
or of NonZeroDigit ::
1
or of HexDigit ::
1
or of OctalDigit :: 1
or
of BinaryDigit
:: 1
is 1.
The MV of DecimalDigit :: 2
or of NonZeroDigit ::
2
or of HexDigit ::
2
or of OctalDigit :: 2
is 2.
The MV of DecimalDigit :: 3
or of NonZeroDigit ::
3
or of HexDigit ::
3
or of OctalDigit :: 3
is 3.
The MV of DecimalDigit :: 4
or of NonZeroDigit ::
4
or of HexDigit ::
4
or of OctalDigit :: 4
is 4.
The MV of DecimalDigit :: 5
or of NonZeroDigit ::
5
or of HexDigit ::
5
or of OctalDigit :: 5
is 5.
The MV of DecimalDigit :: 6
or of NonZeroDigit ::
6
or of HexDigit ::
6
or of OctalDigit :: 6
is 6.
The MV of DecimalDigit :: 7
or of NonZeroDigit ::
7
or of HexDigit ::
7
or of OctalDigit :: 7
is 7.
The MV of DecimalDigit :: 8
or of NonZeroDigit ::
8
or of HexDigit ::
8
is 8.
The MV of DecimalDigit :: 9
or of NonZeroDigit ::
9
or of HexDigit ::
9
is 9.
The MV of HexDigit :: a
or of HexDigit :: A
is 10.
The MV of HexDigit :: b
or of HexDigit :: B
is 11.
The MV of HexDigit :: c
or of HexDigit :: C
is 12.
The MV of HexDigit :: d
or of HexDigit :: D
is 13.
The MV of HexDigit :: e
or of HexDigit :: E
is 14.
The MV of HexDigit :: f
or of HexDigit :: F
is 15.
The MV of BinaryIntegerLiteral :: 0b
BinaryDigits is the MV of BinaryDigits.
The MV of BinaryIntegerLiteral :: 0B
BinaryDigits is the MV of BinaryDigits.
The MV of BinaryDigits :: BinaryDigit is the MV of BinaryDigit.
The MV of BinaryDigits :: BinaryDigits BinaryDigit is (the MV of BinaryDigits × 2) plus the MV of BinaryDigit.
The MV of OctalIntegerLiteral :: 0o
OctalDigits is the MV of OctalDigits.
The MV of OctalIntegerLiteral :: 0O
OctalDigits is the MV of OctalDigits.
The MV of OctalDigits :: OctalDigit is the MV of OctalDigit.
The MV of OctalDigits :: OctalDigits OctalDigit is (the MV of OctalDigits × 8) plus the MV of OctalDigit.
The MV of HexIntegerLiteral :: 0x
HexDigits is the MV of HexDigits.
The MV of HexIntegerLiteral :: 0X
HexDigits is the MV of HexDigits.
The MV of HexDigits :: HexDigit is the MV of HexDigit.
The MV of HexDigits :: HexDigits HexDigit is (the MV of HexDigits × 16) plus the MV of HexDigit.
Once the exact MV for a numeric literal has been determined, it is then rounded to a value of the Number type. If the
MV is 0, then the rounded value is +0; otherwise, the rounded value must be the Number value
for the MV (as specified in 6.1.6), unless the literal is a DecimalLiteral and the literal has more than 20 significant digits, in which case the Number value may
be either the Number value for the MV of a literal produced by replacing each significant digit after the 20th with a
0
digit or the Number value for the MV of a literal produced by replacing each significant digit after the
20th with a 0
digit and then incrementing the literal at the 20th significant digit position. A digit is
significant if it is not part of an ExponentPart and
0
; orNOTE 1 A string literal is zero or more Unicode code points enclosed in single or double quotes. Unicode code points may also be represented by an escape sequence. All code points may appear literally in a string literal except for the closing quote code points, U+005C (REVERSE SOLIDUS), U+000D (CARRIAGE RETURN), U+2028 (LINE SEPARATOR), U+2029 (PARAGRAPH SEPARATOR), and U+000A (LINE FEED). Any code points may appear in the form of an escape sequence. String literals evaluate to ECMAScript String values. When generating these String values Unicode code points are UTF-16 encoded as defined in 10.1.1. Code points belonging to the Basic Multilingual Plane are encoded as a single code unit element of the string. All other code points are encoded as two code unit elements of the string.
"
DoubleStringCharactersopt "
'
SingleStringCharactersopt '
"
or \
or LineTerminator\
EscapeSequence'
or \
or LineTerminator\
EscapeSequence\
LineTerminatorSequence0
[lookahead ∉ DecimalDigit]A conforming implementation, when processing strict mode code (see 10.2.1), must not extend the syntax of EscapeSequence to include LegacyOctalEscapeSequence as described in B.1.2.
'
"
\
b
f
n
r
t
v
x
u
x
HexDigit HexDigitu
Hex4Digitsu{
HexDigits }
The definition of the nonterminal HexDigit is given in 11.8.3. SourceCharacter is defined in 10.1.
NOTE 2 A line terminator code point cannot appear in a string literal, except as part of a
LineContinuation to produce the empty code points sequence. The proper way to cause a line
terminator code point to be part of the String value of a string literal is to use an escape sequence such as
\n
or \u000A
.
u{
HexDigits }
"
DoubleStringCharactersopt "
'
SingleStringCharactersopt '
A string literal stands for a value of the String type. The String value (SV) of the literal is described in terms of code unit values contributed by the various parts of the string literal. As part of this process, some Unicode code points within the string literal are interpreted as having a mathematical value (MV), as described below or in 11.8.3.
The SV of StringLiteral :: ""
is the empty code unit sequence.
The SV of StringLiteral :: ''
is the empty code unit sequence.
The SV of StringLiteral :: "
DoubleStringCharacters "
is the SV of
DoubleStringCharacters.
The SV of StringLiteral :: '
SingleStringCharacters '
is the SV of
SingleStringCharacters.
The SV of DoubleStringCharacters :: DoubleStringCharacter is a sequence of one or two code units that is the SV of DoubleStringCharacter.
The SV of DoubleStringCharacters :: DoubleStringCharacter DoubleStringCharacters is a sequence of one or two code units that is the SV of DoubleStringCharacter followed by all the code units in the SV of DoubleStringCharacters in order.
The SV of SingleStringCharacters :: SingleStringCharacter is a sequence of one or two code units that is the SV of SingleStringCharacter.
The SV of SingleStringCharacters :: SingleStringCharacter SingleStringCharacters is a sequence of one or two code units that is the SV of SingleStringCharacter followed by all the code units in the SV of SingleStringCharacters in order.
The SV of DoubleStringCharacter :: SourceCharacter but not one of "
or \
or LineTerminator is the UTF16Encoding (10.1.1) of the code point value of SourceCharacter.
The SV of DoubleStringCharacter :: \
EscapeSequence is the SV of the EscapeSequence.
The SV of DoubleStringCharacter :: LineContinuation is the empty code unit sequence.
The SV of SingleStringCharacter :: SourceCharacter but not one of '
or \
or LineTerminator is the UTF16Encoding (10.1.1) of the code point value of SourceCharacter.
The SV of SingleStringCharacter :: \
EscapeSequence is the SV of the EscapeSequence.
The SV of SingleStringCharacter :: LineContinuation is the empty code unit sequence.
The SV of EscapeSequence :: CharacterEscapeSequence is the SV of the CharacterEscapeSequence.
The SV of EscapeSequence :: 0
is the code unit value 0.
The SV of EscapeSequence :: HexEscapeSequence is the SV of the HexEscapeSequence.
The SV of EscapeSequence :: UnicodeEscapeSequence is the SV of the UnicodeEscapeSequence.
The SV of CharacterEscapeSequence :: SingleEscapeCharacter is the code unit whose value is determined by the SingleEscapeCharacter according to Table 34.
Escape Sequence | Code Unit Value | Unicode Character Name | Symbol |
---|---|---|---|
\b |
0x0008 |
BACKSPACE | <BS> |
\t |
0x0009 |
CHARACTER TABULATION | <HT> |
\n |
0x000A |
LINE FEED (LF) | <LF> |
\v |
0x000B |
LINE TABULATION | <VT> |
\f |
0x000C |
FORM FEED (FF) | <FF> |
\r |
0x000D |
CARRIAGE RETURN (CR) | <CR> |
\" |
0x0022 |
QUOTATION MARK | " |
\' |
0x0027 |
APOSTROPHE | ' |
\\ |
0x005C |
REVERSE SOLIDUS | \ |
The SV of CharacterEscapeSequence :: NonEscapeCharacter is the SV of the NonEscapeCharacter.
The SV of NonEscapeCharacter :: SourceCharacter but not one of EscapeCharacter or LineTerminator is the UTF16Encoding (10.1.1) of the code point value of SourceCharacter.
The SV of HexEscapeSequence :: x
HexDigit HexDigit is the code unit value
that is (16 times the MV of the first HexDigit) plus the MV of the second HexDigit.
The SV of UnicodeEscapeSequence :: u
Hex4Digits is the SV of Hex4Digits.
The SV of Hex4Digits :: HexDigit HexDigit HexDigit HexDigit is the code unit value that is (4096 times the MV of the first HexDigit) plus (256 times the MV of the second HexDigit) plus (16 times the MV of the third HexDigit) plus the MV of the fourth HexDigit.
The SV of UnicodeEscapeSequence :: u{
HexDigits }
is the UTF16Encoding (10.1.1) of the MV of
HexDigits.
NOTE 1 A regular expression literal is an input element that is converted to a RegExp object
(see 21.2) each time the literal is evaluated. Two regular
expression literals in a program evaluate to regular expression objects that never compare as ===
to each
other even if the two literals' contents are identical. A RegExp object may also be created at runtime by new
RegExp
or calling the RegExp
constructor as a function (see
21.2.3).
The productions below describe the syntax for a regular expression literal and are used by the input element scanner to find the end of the regular expression literal. The source text comprising the RegularExpressionBody and the RegularExpressionFlags are subsequently parsed again using the more stringent ECMAScript Regular Expression grammar (21.2.1).
An implementation may extend the ECMAScript Regular Expression grammar defined in 21.2.1, but it must not extend the RegularExpressionBody and RegularExpressionFlags productions defined below or the productions used by these productions.
/
RegularExpressionBody /
RegularExpressionFlags*
or \
or /
or [
\
or /
or [
\
RegularExpressionNonTerminator[
RegularExpressionClassChars ]
]
or \
NOTE 2 Regular expression literals may not be empty; instead of representing an empty regular
expression literal, the code unit sequence //
starts a single-line comment. To specify an empty regular
expression, use: /(?:)/
.
/
RegularExpressionBody /
RegularExpressionFlags/
RegularExpressionBody /
RegularExpressionFlags`
TemplateCharactersopt `
`
TemplateCharactersopt ${
}
TemplateCharactersopt ${
}
TemplateCharactersopt `
$
[lookahead ≠ { ]\
EscapeSequence`
or \
or $
or LineTerminatorA conforming implementation must not use the extended definition of EscapeSequence described in B.1.2 when parsing a TemplateCharacter.
NOTE TemplateSubstitutionTail is used by the InputElementTemplateTail alternative lexical goal.
A template literal component is interpreted as a sequence of Unicode code points. The Template Value (TV) of a literal component is described in terms of code unit values (SV, 11.8.4) contributed by the various parts of the template literal component. As part of this process, some Unicode code points within the template component are interpreted as having a mathematical value (MV, 11.8.3). In determining a TV, escape sequences are replaced by the UTF-16 code unit(s) of the Unicode code point represented by the escape sequence. The Template Raw Value (TRV) is similar to a Template Value with the difference that in TRVs escape sequences are interpreted literally.
The TV and TRV of NoSubstitutionTemplate ::
``
is the empty code unit sequence.
The TV and TRV of TemplateHead :: `${
is the empty code unit sequence.
The TV and TRV of TemplateMiddle :: }${
is the empty code unit sequence.
The TV and TRV of TemplateTail :: }`
is the empty code unit sequence.
The TV of NoSubstitutionTemplate :: `
TemplateCharacters `
is the TV of
TemplateCharacters.
The TV of TemplateHead :: `
TemplateCharacters ${
is the TV of
TemplateCharacters.
The TV of TemplateMiddle :: }
TemplateCharacters ${
is the TV of
TemplateCharacters.
The TV of TemplateTail :: }
TemplateCharacters `
is the TV of
TemplateCharacters.
The TV of TemplateCharacters :: TemplateCharacter is the TV of TemplateCharacter.
The TV of TemplateCharacters :: TemplateCharacter TemplateCharacters is a sequence consisting of the code units in the TV of TemplateCharacter followed by all the code units in the TV of TemplateCharacters in order.
The TV of TemplateCharacter :: SourceCharacter but not one of `
or \
or $
or LineTerminator is the UTF16Encoding (10.1.1) of the code point value of
SourceCharacter.
The TV of TemplateCharacter :: $
is the code unit value 0x0024.
The TV of TemplateCharacter :: \
EscapeSequence is the SV of EscapeSequence.
The TV of TemplateCharacter :: LineContinuation is the TV of LineContinuation.
The TV of TemplateCharacter :: LineTerminatorSequence is the TRV of LineTerminatorSequence.
The TV of LineContinuation :: \
LineTerminatorSequence is the empty code unit sequence.
The TRV of NoSubstitutionTemplate :: `
TemplateCharacters `
is the TRV of
TemplateCharacters.
The TRV of TemplateHead :: `
TemplateCharacters ${
is the TRV of
TemplateCharacters.
The TRV of TemplateMiddle :: }
TemplateCharacters ${
is the TRV of
TemplateCharacters.
The TRV of TemplateTail :: }
TemplateCharacters `
is the TRV of
TemplateCharacters.
The TRV of TemplateCharacters :: TemplateCharacter is the TRV of TemplateCharacter.
The TRV of TemplateCharacters :: TemplateCharacter TemplateCharacters is a sequence consisting of the code units in the TRV of TemplateCharacter followed by all the code units in the TRV of TemplateCharacters, in order.
The TRV of TemplateCharacter :: SourceCharacter but not one of `
or \
or $
or LineTerminator is the UTF16Encoding (10.1.1) of the code point value of
SourceCharacter.
The TRV of TemplateCharacter :: $
is the code unit value 0x0024.
The TRV of TemplateCharacter :: \
EscapeSequence is the sequence consisting of the code unit value
0x005C followed by the code units of TRV of EscapeSequence.
The TRV of TemplateCharacter :: LineContinuation is the TRV of LineContinuation.
The TRV of TemplateCharacter :: LineTerminatorSequence is the TRV of LineTerminatorSequence.
The TRV of EscapeSequence :: CharacterEscapeSequence is the TRV of the CharacterEscapeSequence.
The TRV of EscapeSequence :: 0
is the code unit value 0x0030.
The TRV of EscapeSequence :: HexEscapeSequence is the TRV of the HexEscapeSequence.
The TRV of EscapeSequence :: UnicodeEscapeSequence is the TRV of the UnicodeEscapeSequence.
The TRV of CharacterEscapeSequence :: SingleEscapeCharacter is the TRV of the SingleEscapeCharacter.
The TRV of CharacterEscapeSequence :: NonEscapeCharacter is the SV of the NonEscapeCharacter.
The TRV of SingleEscapeCharacter :: one of '
"
\
b
f
n
r
t
v
is the SV of the SourceCharacter that is that single code point.
The TRV of HexEscapeSequence :: x
HexDigit HexDigit is the sequence
consisting of code unit value 0x0078 followed by TRV of the first HexDigit followed by the TRV of the second
HexDigit.
The TRV of UnicodeEscapeSequence :: u
Hex4Digits is the sequence consisting of code unit value 0x0075
followed by TRV of Hex4Digits.
The TRV of UnicodeEscapeSequence :: u{
HexDigits }
is the sequence consisting of
code unit value 0x0075 followed by code unit value 0x007B followed by TRV of HexDigits followed by code unit
value 0x007D.
The TRV of Hex4Digits :: HexDigit HexDigit HexDigit HexDigit is the sequence consisting of the TRV of the first HexDigit followed by the TRV of the second HexDigit followed by the TRV of the third HexDigit followed by the TRV of the fourth HexDigit.
The TRV of HexDigits :: HexDigit is the TRV of HexDigit.
The TRV of HexDigits :: HexDigits HexDigit is the sequence consisting of TRV of HexDigits followed by TRV of HexDigit.
The TRV of a HexDigit is the SV of the SourceCharacter that is that HexDigit.
The TRV of LineContinuation :: \
LineTerminatorSequence is the sequence consisting of the code unit
value 0x005C followed by the code units of TRV of LineTerminatorSequence.
The TRV of LineTerminatorSequence :: <LF> is the code unit value 0x000A.
The TRV of LineTerminatorSequence :: <CR> is the code unit value 0x000A.
The TRV of LineTerminatorSequence :: <LS> is the code unit value 0x2028.
The TRV of LineTerminatorSequence :: <PS> is the code unit value 0x2029.
The TRV of LineTerminatorSequence :: <CR><LF> is the sequence consisting of the code unit value 0x000A.
NOTE TV excludes the code units of LineContinuation while TRV includes them. <CR><LF> and <CR> LineTerminatorSequences are normalized to <LF> for both TV and TRV. An explicit EscapeSequence is needed to include a <CR> or <CR><LF> sequence.
Certain ECMAScript statements (empty statement, let
, const
, import
, and
export
declarations, variable statement, expression statement, debugger
statement,
continue
statement, break
statement, return
statement, and throw
statement) must be terminated with semicolons. Such semicolons may always appear explicitly in the source text. For
convenience, however, such semicolons may be omitted from the source text in certain situations. These situations are
described by saying that semicolons are automatically inserted into the source code token stream in those situations.
In the following rules, “token” means the actual recognized lexical token determined using the current lexical goal symbol as described in clause 11.
There are three basic rules of semicolon insertion:
The offending token is separated from the previous token by at least one LineTerminator.
The offending token is }
.
The previous token is )
and the inserted semicolon would then be parsed as the terminating semicolon
of a do-while statement (13.7.2).
However, there is an additional overriding condition on the preceding rules: a semicolon is never inserted automatically
if the semicolon would then be parsed as an empty statement or if that semicolon would become one of the two semicolons in
the header of a for
statement (see 13.7.4).
NOTE The following are the only restricted productions in the grammar:
++
--
continue;
continue
[no LineTerminator here] LabelIdentifier[?Yield] ;
break
;
break
[no LineTerminator here] LabelIdentifier[?Yield] ;
return
[no LineTerminator here] Expression ;
return
[no LineTerminator here] Expression[In, ?Yield] ;
throw
[no LineTerminator here] Expression[In, ?Yield] ;
=>
ConciseBody[?In]yield
[no LineTerminator here] *
AssignmentExpression[?In, Yield]yield
[no LineTerminator here] AssignmentExpression[?In, Yield]The practical effect of these restricted productions is as follows:
When a ++
or --
token is encountered where the parser would treat it as a postfix
operator, and at least one LineTerminator occurred between the preceding token and the
++
or --
token, then a semicolon is automatically inserted before the ++
or
--
token.
When a continue
, break
, return
, throw
, or yield
token is encountered and a LineTerminator is encountered before the next token, a semicolon is
automatically inserted after the continue
, break
, return
, throw
,
or yield
token.
The resulting practical advice to ECMAScript programmers is:
A postfix ++
or --
operator should appear on the same line as its operand.
An Expression in a return
or throw
statement or an AssignmentExpression in a yield
expression should start on the same line as the
return
, throw
, or yield
token.
An IdentifierReference in a break
or continue
statement should be
on the same line as the break
or continue
token.
The source
{ 1 2 } 3
is not a valid sentence in the ECMAScript grammar, even with the automatic semicolon insertion rules. In contrast, the source
{ 1
2 } 3
is also not a valid ECMAScript sentence, but is transformed by automatic semicolon insertion into the following:
{ 1
;2 ;} 3;
which is a valid ECMAScript sentence.
The source
for (a; b
)
is not a valid ECMAScript sentence and is not altered by automatic semicolon
insertion because the semicolon is needed for the header of a for
statement. Automatic semicolon insertion
never inserts one of the two semicolons in the header of a for
statement.
The source
return
a + b
is transformed by automatic semicolon insertion into the following:
return;
a + b;
NOTE 1 The expression a + b
is not treated as a value to be returned by the
return
statement, because a LineTerminator separates it from the token
return
.
The source
a = b
++c
is transformed by automatic semicolon insertion into the following:
a = b;
++c;
NOTE 2 The token ++
is not treated as a postfix operator applying to the variable
b
, because a LineTerminator occurs between b
and ++
.
The source
if (a > b)
else c = d
is not a valid ECMAScript sentence and is not altered by automatic semicolon
insertion before the else
token, even though no production of the grammar applies at that point, because an
automatically inserted semicolon would then be parsed as an empty statement.
The source
a = b + c
(d + e).print()
is not transformed by automatic semicolon insertion, because the parenthesized expression that begins the second line can be interpreted as an argument list for a function call:
a = b + c(d + e).print()
In the circumstance that an assignment statement must begin with a left parenthesis, it is a good idea for the programmer to provide an explicit semicolon at the end of the preceding statement rather than to rely on automatic semicolon insertion.
Syntax
yield
yield
yield
It is a Syntax Error if the code matched by this production is contained in strict
mode code and the StringValue of Identifier is "arguments"
or
"eval"
.
IdentifierReference : yield
BindingIdentifier :
yield
LabelIdentifier :
yield
It is a Syntax Error if the code matched by this production is contained in strict mode code.
IdentifierReference[Yield] : Identifier
BindingIdentifier[Yield] : Identifier
LabelIdentifier[Yield] :
Identifier
It is a Syntax Error if this production has a [Yield] parameter and StringValue of Identifier is "yield"
.
It is a Syntax Error if this phrase is contained in strict mode code and the
StringValue of IdentifierName is: "implements"
, "interface"
,
"let"
, "package"
, "private"
, "protected"
, "public"
,
"static"
, or "yield"
.
It is a Syntax Error if StringValue of IdentifierName is the same String value as the
StringValue of any ReservedWord except for yield
.
NOTE StringValue of IdentifierName normalizes any Unicode escape sequences in IdentifierName hence such escapes cannot be used to write an Identifier whose code point sequence is the same as a ReservedWord.
See also: 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
yield
"yield"
.See also: 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
"eval"
or "arguments"
, return false.yield
IdentifierReference : yield
BindingIdentifier :
yield
LabelIdentifier :
yield
"yield"
.With arguments value and environment.
NOTE undefined is passed for environment to indicate that a PutValue operation should be used to assign the initialization value. This is the case for
var
statements and formal parameter lists of some non-strict functions (See 9.2.12). In those cases a lexical binding is hoisted and preinitialized
prior to evaluation of its initializer.
yield
"yield"
, value,
environment).yield
"yield"
).NOTE 1 The result of evaluating an IdentifierReference is always a value of type Reference.
NOTE 2 In non-strict code, the keyword yield
may be used as an identifier. Evaluating the IdentifierReference production resolves the binding
of yield
as if it was an Identifier. Early Error restriction ensures that such an
evaluation only can occur for non-strict code. See 13.3.1 for the handling of yield
in binding creation contexts.
this
(
Expression[In, ?Yield] )
(
)
(
...
BindingIdentifier[?Yield] )
(
Expression[In, ?Yield] ,
...
BindingIdentifier[?Yield] )
When processing the production
PrimaryExpression[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]
the interpretation of CoverParenthesizedExpressionAndArrowParameterList is refined using the following grammar:
(
Expression[In, ?Yield] )
(
Expression[In, ?Yield] )
See also: 14.1.8, 14.2.7, 14.4.7, 14.5.6.
See also: 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
this
See also: 12.3.1.4.
this
See also: 12.1.3, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
this
this
Keywordthis
See 12.1 for IdentifierReference.
false
.true
.NOTE An ArrayLiteral is an expression describing the initialization of an Array object, using a list, of zero or more expressions each of which represents an array element, enclosed in square brackets. The elements need not be literals; they are evaluated each time the array initializer is evaluated.
Array elements may be elided at the beginning, middle or end of the element list. Whenever a comma in the element list is not preceded by an AssignmentExpression (i.e., a comma at the beginning or after another comma), the missing array element contributes to the length of the Array and increases the index of subsequent elements. Elided array elements are not defined. If an element is elided at the end of an array, that element does not contribute to the length of the Array.
[
Elisionopt ]
[
ElementList[?Yield] ]
[
ElementList[?Yield] ,
Elisionopt ]
,
Elisionopt AssignmentExpression[In, ?Yield],
Elisionopt SpreadElement[?Yield],
,
...
AssignmentExpression[In, ?Yield],
,
With parameters array and nextIndex.
,
Elisionopt AssignmentExpression,
Elisionopt SpreadElement...
AssignmentExpressionNOTE CreateDataProperty is used to ensure that own properties are defined for the array even if the standard built-in Array prototype object has been modified in a manner that would preclude the creation of new own properties using [[Set]].
[
Elisionopt ]
"length"
, pad, false).[
ElementList ]
"length"
, len, false).[
ElementList ,
Elisionopt ]
"length"
, ToUint32(padding+len), false).NOTE 1 An object initializer is an expression describing the initialization of an Object, written in a form resembling a literal. It is a list of zero or more pairs of property keys and associated values, enclosed in curly brackets. The values need not be literals; they are evaluated each time the object initializer is evaluated.
{
}
{
PropertyDefinitionList[?Yield] }
{
PropertyDefinitionList[?Yield] ,
}
,
PropertyDefinition[?Yield]:
AssignmentExpression[In, ?Yield][
AssignmentExpression[In, ?Yield] ]
=
AssignmentExpression[?In, ?Yield]NOTE 2 MethodDefinition is defined in 14.3.
NOTE 3 In certain contexts, ObjectLiteral is used as a cover grammar for a more restricted secondary grammar. The CoverInitializedName production is necessary to fully cover these secondary grammars. However, use of this production results in an early Syntax Error in normal contexts where an actual ObjectLiteral is expected.
In addition to describing an actual object initializer the ObjectLiteral productions are also used as a cover grammar for ObjectAssignmentPattern (12.14.5). and may be recognized as part of a CoverParenthesizedExpressionAndArrowParameterList. When ObjectLiteral appears in a context where ObjectAssignmentPattern is required the following Early Error rules are not applied. In addition, they are not applied when initially parsing a CoverParenthesizedExpressionAndArrowParameterList.
NOTE This production exists so that ObjectLiteral can serve as a cover grammar for ObjectAssignmentPattern (12.14.5). It cannot occur in an actual object initializer.
With parameter symbol.
See also: 14.3.2, 14.4.3, 14.5.5.
With parameter symbol.
See also: 5.3, 12.3.1.1, 14.1.4, 14.2.3, 14.4.4, 14.5.4.
NOTE Static semantic rules that depend upon substructure generally do not look into function definitions.
,
PropertyDefinition:
AssignmentExpressionSee also: 14.3.6, 14.4.10, 14.5.12
:
AssignmentExpression[
AssignmentExpression ]
,
PropertyDefinition{
}
{
PropertyDefinitionList }
{
PropertyDefinitionList ,
}
[
AssignmentExpression ]
With parameter object and enumerable.
See also: 14.3.9, 14.4.13, B.3.1
,
PropertyDefinition:
AssignmentExpression"name"
).NOTE An alternative semantics for this production is given in B.3.1.
See 14.1 for PrimaryExpression : FunctionExpression .
See 14.4 for PrimaryExpression : GeneratorExpression .
See 14.5 for PrimaryExpression : ClassExpression .
It is a Syntax Error if BodyText of RegularExpressionLiteral cannot be recognized using the goal symbol Pattern of the ECMAScript RegExp grammar specified in 21.2.1.
It is a Syntax Error if FlagText of RegularExpressionLiteral contains any code points other than "g"
, "i"
,
"m"
, "u"
, or "y"
, or if it contains the same code point more than once.
With parameter raw.
See also: 12.3.6.1
The abstract operation GetTemplateObject is called with a grammar production, templateLiteral, as an argument. It performs the following steps:
"frozen"
)."raw"
, PropertyDescriptor{[[Value]]:
rawObj, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
false})."frozen"
).NOTE 1 The creation of a template object cannot result in an abrupt completion.
NOTE 2 Each TemplateLiteral in the program code of a Realm is associated with a unique template object that is used in the evaluation of tagged Templates (12.2.9.5). The template objects are frozen and the same template object is used each time a specific tagged Template is evaluated. Whether template objects are created lazily upon first evaluation of the TemplateLiteral or eagerly prior to first evaluation is an implementation choice that is not observable to ECMAScript code.
NOTE 3 Future editions of this specification may define additional non-enumerable properties of template objects.
NOTE 1 The string conversion semantics applied to the Expression
value are like String.prototype.concat
rather than the
+
operator.
NOTE 2 The string conversion semantics applied to the Expression
value are like String.prototype.concat
rather than the
+
operator.
NOTE 3 The string conversion semantics applied to the Expression
value are like String.prototype.concat
rather than the
+
operator.
It is a Syntax Error if the lexical token sequence matched by CoverParenthesizedExpressionAndArrowParameterList cannot be parsed with no tokens left over using ParenthesizedExpression as the goal symbol.
All Early Errors rules for ParenthesizedExpression and its derived productions also apply to CoveredParenthesizedExpression of CoverParenthesizedExpressionAndArrowParameterList.
See also: 12.2.1.3, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
(
Expression )
See also: 12.1.3, 12.2.1.5, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
(
Expression )
(
Expression )
NOTE This algorithm does not apply GetValue to the result of
evaluating Expression. The principal motivation for this is so that operators such as
delete
and typeof
may be applied to parenthesized expressions.
[
Expression[In, ?Yield] ]
.
IdentifierNamenew
MemberExpression[?Yield] Arguments[?Yield]super
[
Expression[In, ?Yield] ]
super
.
IdentifierNamenew
.
target
new
NewExpression[?Yield][
Expression[In, ?Yield] ]
.
IdentifierNamesuper
Arguments[?Yield](
)
(
ArgumentList[?Yield] )
...
AssignmentExpression[In, ?Yield],
AssignmentExpression[In, ?Yield],
...
AssignmentExpression[In, ?Yield]With parameter symbol.
See also: 5.3, 12.2.6.3, 14.1.4, 14.2.3, 14.4.4, 14.5.4
.
IdentifierNamesuper
.
IdentifierNamesuper
, return true..
IdentifierNameSee also: 12.2.1.3, 12.2.10.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
[
Expression ]
.
IdentifierNamenew
MemberExpression Argumentsnew
NewExpression[
Expression ]
.
IdentifierNameSee also: 13.7.5.6.
[
Expression ]
.
IdentifierNamenew
MemberExpression Argumentsnew
NewExpression[
Expression ]
.
IdentifierNameSee also: 12.2.1.4.
[
Expression ]
.
IdentifierNamenew
MemberExpression Argumentsnew
NewExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
[
Expression ]
.
IdentifierName[
Expression ]
.
IdentifierNamenew
NewExpressionnew
MemberExpression Argumentsnew
.
target
NOTE Properties are accessed by name, using either the dot notation:
.
IdentifierName.
IdentifierNameor the bracket notation:
[
Expression ]
[
Expression ]
The dot notation is explained by the following syntactic conversion:
.
IdentifierNameis identical in its behaviour to
[
<identifier-name-string> ]
and similarly
.
IdentifierNameis identical in its behaviour to
[
<identifier-name-string> ]
where <identifier-name-string> is the result of evaluating StringValue of IdentifierName.
[
Expression ]
.
IdentifierName[
Expression ]
Is evaluated in exactly the same manner as MemberExpression : MemberExpression [
Expression ]
except that the contained CallExpression is evaluated in step 1.
.
IdentifierNameIs evaluated in exactly the same manner as MemberExpression : MemberExpression .
IdentifierName except that the contained CallExpression is evaluated
in step 1.
new
Operatornew
NewExpressionnew
MemberExpression ArgumentsThe abstract operation EvaluateNew with arguments constructProduction, and arguments performs the following steps:
"eval"
, then
A CallExpression evaluation that executes step 4.a.vii is a direct eval.
The abstract operation EvaluateCall takes as arguments a value ref, a syntactic grammar production arguments, and a Boolean argument tailPosition. It performs the following steps:
The abstract operation EvaluateDirectCall takes as arguments a value func, a value thisValue, a syntactic grammar production arguments, and a Boolean argument tailPosition. It performs the following steps:
super
Keywordsuper
[
Expression ]
super
.
IdentifierNamesuper
ArgumentsThe abstract operation GetSuperConstructor performs the following steps:
The abstract operation MakeSuperPropertyReference with arguments propertyKey and strict performs the following steps:
See also: 12.2.9.2
(
)
...
AssignmentExpression,
AssignmentExpression,
...
AssignmentExpressionnew
.
target
++
--
++
--
It is an early Reference Error if IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8
++
--
See also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
++
--
++
1
to oldValue, using the same rules as for
the +
operator (see 12.7.5).--
1
from oldValue, using the same rules
as for the -
operator (12.7.5).delete
UnaryExpression[?Yield]void
UnaryExpression[?Yield]typeof
UnaryExpression[?Yield]++
UnaryExpression[?Yield]--
UnaryExpression[?Yield]+
UnaryExpression[?Yield]-
UnaryExpression[?Yield]~
UnaryExpression[?Yield]!
UnaryExpression[?Yield]++
UnaryExpression--
UnaryExpressionIt is an early Reference Error if IsValidSimpleAssignmentTarget of UnaryExpression is false.
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
delete
UnaryExpressionvoid
UnaryExpressiontypeof
UnaryExpression++
UnaryExpression--
UnaryExpression+
UnaryExpression-
UnaryExpression~
UnaryExpression!
UnaryExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
delete
UnaryExpressionvoid
UnaryExpressiontypeof
UnaryExpression++
UnaryExpression--
UnaryExpression+
UnaryExpression-
UnaryExpression~
UnaryExpression!
UnaryExpressiondelete
Operatordelete
UnaryExpressionIt is a Syntax Error if the UnaryExpression is contained in strict mode code and the derived UnaryExpression is PrimaryExpression : IdentifierReference.
It is a Syntax Error if the derived UnaryExpression is
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
and CoverParenthesizedExpressionAndArrowParameterList ultimately derives a phrase that, if used in place
of UnaryExpression, would produce a Syntax Error according to these rules. This rule is recursively
applied.
NOTE The last rule means that expressions such as
delete
(((foo)))
produce early errors because of recursive application of the first rule.
delete
UnaryExpressionNOTE When a delete
operator occurs within strict
mode code, a SyntaxError exception is thrown if its UnaryExpression is a direct
reference to a variable, function argument, or function name. In addition, if a delete
operator occurs
within strict mode code and the property to be deleted has the attribute {
[[Configurable]]: false }, a TypeError exception is thrown.
void
Operatorvoid
UnaryExpressionNOTE GetValue must be called even though its value is not used because it may have observable side-effects.
typeof
Operatortypeof
UnaryExpression"undefined"
.Type of val | Result |
---|---|
Undefined | "undefined" |
Null | "object" |
Boolean | "boolean" |
Number | "number" |
String | "string" |
Symbol | "symbol" |
Object (ordinary and does not implement [[Call]]) | "object" |
Object (standard exotic and does not implement [[Call]]) | "object" |
Object (implements [[Call]]) | "function" |
Object (non-standard exotic and does not implement [[Call]]) | Implementation-defined. Must not be "undefined" , "boolean" , "function" , "number" , "symbol" , or "string". |
NOTE Implementations are discouraged from defining new typeof
result values for
non-standard exotic objects. If possible "object"
should be used for such objects.
++
UnaryExpression1
to oldValue, using the same rules as for
the +
operator (see 12.7.5).--
UnaryExpression1
from oldValue, using the same
rules as for the -
operator (see
12.7.5).+
OperatorNOTE The unary + operator converts its operand to Number type.
+
UnaryExpression-
OperatorNOTE The unary -
operator converts its operand to Number type and then negates
it. Negating +0 produces −0, and negating −0 produces +0.
-
UnaryExpression~
)~
UnaryExpression!
)!
UnaryExpression*
/
%
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
MultiplicativeExpression : MultiplicativeExpression MultiplicativeOperator UnaryExpression
See also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
MultiplicativeExpression : MultiplicativeExpression MultiplicativeOperator UnaryExpression
MultiplicativeExpression : MultiplicativeExpression MultiplicativeOperator UnaryExpression
*
OperatorThe *
MultiplicativeOperator performs multiplication, producing the product of its
operands. Multiplication is commutative. Multiplication is not always associative in ECMAScript, because of finite
precision.
The result of a floating-point multiplication is governed by the rules of IEEE 754-2008 binary double-precision arithmetic:
If either operand is NaN, the result is NaN.
The sign of the result is positive if both operands have the same sign, negative if the operands have different signs.
Multiplication of an infinity by a zero results in NaN.
Multiplication of an infinity by an infinity results in an infinity. The sign is determined by the rule already stated above.
Multiplication of an infinity by a finite nonzero value results in a signed infinity. The sign is determined by the rule already stated above.
In the remaining cases, where neither an infinity nor NaN is involved, the product is computed and rounded to the nearest representable value using IEEE 754-2008 round-to-nearest mode. If the magnitude is too large to represent, the result is then an infinity of appropriate sign. If the magnitude is too small to represent, the result is then a zero of appropriate sign. The ECMAScript language requires support of gradual underflow as defined by IEEE 754-2008.
/
OperatorThe /
MultiplicativeOperator performs division, producing the quotient of its
operands. The left operand is the dividend and the right operand is the divisor. ECMAScript does not perform integer
division. The operands and result of all division operations are double-precision floating-point numbers. The result of
division is determined by the specification of IEEE 754-2008 arithmetic:
If either operand is NaN, the result is NaN.
The sign of the result is positive if both operands have the same sign, negative if the operands have different signs.
Division of an infinity by an infinity results in NaN.
Division of an infinity by a zero results in an infinity. The sign is determined by the rule already stated above.
Division of an infinity by a nonzero finite value results in a signed infinity. The sign is determined by the rule already stated above.
Division of a finite value by an infinity results in zero. The sign is determined by the rule already stated above.
Division of a zero by a zero results in NaN; division of zero by any other finite value results in zero, with the sign determined by the rule already stated above.
Division of a nonzero finite value by a zero results in a signed infinity. The sign is determined by the rule already stated above.
In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, the quotient is computed and rounded to the nearest representable value using IEEE 754-2008 round-to-nearest mode. If the magnitude is too large to represent, the operation overflows; the result is then an infinity of appropriate sign. If the magnitude is too small to represent, the operation underflows and the result is a zero of the appropriate sign. The ECMAScript language requires support of gradual underflow as defined by IEEE 754-2008.
%
OperatorThe %
MultiplicativeOperator yields the remainder of its operands from an implied
division; the left operand is the dividend and the right operand is the divisor.
NOTE In C and C++, the remainder operator accepts only integral operands; in ECMAScript, it also accepts floating-point operands.
The result of a floating-point remainder operation as computed by the %
operator is not the same as the
“remainder” operation defined by IEEE 754-2008. The IEEE 754-2008 “remainder” operation computes
the remainder from a rounding division, not a truncating division, and so its behaviour is not analogous to that of the
usual integer remainder operator. Instead the ECMAScript language defines %
on floating-point operations to
behave in a manner analogous to that of the Java integer remainder operator; this may be compared with the C library
function fmod.
The result of an ECMAScript floating-point remainder operation is determined by the rules of IEEE arithmetic:
If either operand is NaN, the result is NaN.
The sign of the result equals the sign of the dividend.
If the dividend is an infinity, or the divisor is a zero, or both, the result is NaN.
If the dividend is finite and the divisor is an infinity, the result equals the dividend.
If the dividend is a zero and the divisor is nonzero and finite, the result is the same as the dividend.
In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, the floating-point remainder r from a dividend n and a divisor d is defined by the mathematical relation r = n − (d × q) where q is an integer that is negative only if n/d is negative and positive only if n/d is positive, and whose magnitude is as large as possible without exceeding the magnitude of the true mathematical quotient of n and d. r is computed and rounded to the nearest representable value using IEEE 754-2008 round-to-nearest mode.
+
MultiplicativeExpression[?Yield]-
MultiplicativeExpression[?Yield]See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
+
MultiplicativeExpression-
MultiplicativeExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
+
MultiplicativeExpression-
MultiplicativeExpression+
)NOTE The addition operator either performs string concatenation or numeric addition.
+
MultiplicativeExpressionNOTE 1 No hint is provided in the calls to ToPrimitive in steps 7 and 9. All standard objects except Date objects handle the absence of a hint as if the hint Number were given; Date objects handle the absence of a hint as if the hint String were given. Exotic objects may handle the absence of a hint in some other manner.
NOTE 2 Step 11 differs from step 5 of the Abstract Relational Comparison algorithm (7.2.11), by using the logical-or operation instead of the logical-and operation.
-
)-
MultiplicativeExpressionThe +
operator performs addition when applied to two operands of numeric type, producing the sum of the
operands. The -
operator performs subtraction, producing the difference of two numeric operands.
Addition is a commutative operation, but not always associative.
The result of an addition is determined using the rules of IEEE 754-2008 binary double-precision arithmetic:
If either operand is NaN, the result is NaN.
The sum of two infinities of opposite sign is NaN.
The sum of two infinities of the same sign is the infinity of that sign.
The sum of an infinity and a finite value is equal to the infinite operand.
The sum of two negative zeroes is −0. The sum of two positive zeroes, or of two zeroes of opposite sign, is +0.
The sum of a zero and a nonzero finite value is equal to the nonzero operand.
The sum of two nonzero finite values of the same magnitude and opposite sign is +0.
In the remaining cases, where neither an infinity, nor a zero, nor NaN is involved, and the operands have the same sign or have different magnitudes, the sum is computed and rounded to the nearest representable value using IEEE 754-2008 round-to-nearest mode. If the magnitude is too large to represent, the operation overflows and the result is then an infinity of appropriate sign. The ECMAScript language requires support of gradual underflow as defined by IEEE 754-2008.
NOTE The -
operator performs subtraction when applied to two operands of numeric
type, producing the difference of its operands; the left operand is the minuend and the right operand is the subtrahend.
Given numeric operands a and b, it is always the case that a–
b produces the same result as
a +(–
b)
.
<<
AdditiveExpression[?Yield]>>
AdditiveExpression[?Yield]>>>
AdditiveExpression[?Yield]See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
<<
AdditiveExpression>>
AdditiveExpression>>>
AdditiveExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
<<
AdditiveExpression>>
AdditiveExpression>>>
AdditiveExpression<<
)NOTE Performs a bitwise left shift operation on the left operand by the amount specified by the right operand.
<<
AdditiveExpression>>
)NOTE Performs a sign-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
>>
AdditiveExpression>>>
)NOTE Performs a zero-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
>>>
AdditiveExpressionNOTE 1 The result of evaluating a relational operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
<
ShiftExpression[?Yield]>
ShiftExpression[?Yield]<=
ShiftExpression[? Yield]>=
ShiftExpression[?Yield]instanceof
ShiftExpression[?Yield]in
ShiftExpression[?Yield]NOTE 2 The [In] grammar parameter is needed to avoid confusing the in
operator in
a relational expression with the in
operator in a for
statement.
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
<
ShiftExpression>
ShiftExpression<=
ShiftExpression>=
ShiftExpressioninstanceof
ShiftExpressionin
ShiftExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
<
ShiftExpression>
ShiftExpression<=
ShiftExpression>=
ShiftExpressioninstanceof
ShiftExpressionin
ShiftExpression<
ShiftExpression>
ShiftExpression<=
ShiftExpression>=
ShiftExpressioninstanceof
ShiftExpressionin
ShiftExpressionThe abstract operation InstanceofOperator(O, C) implements the generic algorithm for determining if an object O inherits from the inheritance path defined by constructor C. This abstract operation performs the following steps:
NOTE Steps 5 and 6 provide compatibility with previous editions of ECMAScript that did not use
a @@hasInstance method to define the instanceof
operator semantics. If a function object does not define or
inherit @@hasInstance it uses the default instanceof
semantics.
NOTE The result of evaluating an equality operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
==
RelationalExpression[?In, ?Yield]!=
RelationalExpression[?In, ?Yield]===
RelationalExpression[?In, ?Yield]!==
RelationalExpression[?In, ?Yield]See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
==
RelationalExpression!=
RelationalExpression===
RelationalExpression!==
RelationalExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
==
RelationalExpression!=
RelationalExpression===
RelationalExpression!==
RelationalExpression==
RelationalExpression!=
RelationalExpression===
RelationalExpression!==
RelationalExpressionNOTE 1 Given the above definition of equality:
"" + a == "" + b
.+a == +b
.!a == !b
.NOTE 2 The equality operators maintain the following invariants:
A
!=
B
is equivalent to !(A
==
B)
.A
==
B
is equivalent to B
==
A
, except
in the order of evaluation of A
and B
.NOTE 3 The equality operator is not always transitive. For example, there might be two distinct
String objects, each representing the same String value; each String object would be considered equal to the String value
by the ==
operator, but the two String objects would not be equal to each other. For example:
new String("a") == "a"
and "a" == new String("a")
are both true.new String("a") == new String("a")
is false.NOTE 4 Comparison of Strings uses a simple equality test on sequences of code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore Strings values that are canonically equal according to the Unicode standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized form.
&
EqualityExpression[?In, ?Yield]^
BitwiseANDExpression[?In, ?Yield]|
BitwiseXORExpression[?In, ?Yield]See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
BitwiseANDExpression : BitwiseANDExpression &
EqualityExpression
BitwiseXORExpression : BitwiseXORExpression ^
BitwiseANDExpression
BitwiseORExpression : BitwiseORExpression |
BitwiseXORExpression
See also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.12.2, 12.13.2, 12.14.3, 12.15.2.
BitwiseANDExpression : BitwiseANDExpression &
EqualityExpression
BitwiseXORExpression : BitwiseXORExpression ^
BitwiseANDExpression
BitwiseORExpression : BitwiseORExpression |
BitwiseXORExpression
The production A : A @ B, where @ is one of the bitwise operators in the productions above, is evaluated as follows:
&&
BitwiseORExpression[?In, ?Yield]||
LogicalANDExpression[?In, ?Yield]NOTE The value produced by a &&
or ||
operator is not
necessarily of type Boolean. The value produced will always be the value of one of the two operand expressions.
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
LogicalANDExpression : LogicalANDExpression &&
BitwiseORExpression
LogicalORExpression : LogicalORExpression ||
LogicalANDExpression
See also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.13.2, 12.14.3, 12.15.2.
LogicalANDExpression : LogicalANDExpression &&
BitwiseORExpression
LogicalORExpression : LogicalORExpression ||
LogicalANDExpression
&&
BitwiseORExpression||
LogicalANDExpression? : )
?
AssignmentExpression[In, ?Yield] :
AssignmentExpression[?In, ?Yield]NOTE The grammar for a ConditionalExpression in ECMAScript is slightly different from that in C and Java, which each allow the second subexpression to be an Expression but restrict the third expression to be a ConditionalExpression. The motivation for this difference in ECMAScript is to allow an assignment expression to be governed by either arm of a conditional and to eliminate the confusing and fairly useless case of a comma expression as the centre expression.
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
?
AssignmentExpression :
AssignmentExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.14.3, 12.15.2.
?
AssignmentExpression :
AssignmentExpression?
AssignmentExpression :
AssignmentExpression=
AssignmentExpression[?In, ?Yield]*=
/=
%=
+=
-=
<<=
>>=
>>>=
&=
^=
|=
=
AssignmentExpressionIt is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and the lexical token sequence matched by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.
It is an early Reference Error if LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.
It is an early Reference Error if IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.15.1, 14.1.11, 14.4.9, 14.5.8.
=
AssignmentExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.15.2.
=
AssignmentExpressionAssignmentExpression[In, Yield] : LeftHandSideExpression[?Yield] =
AssignmentExpression[?In, ?Yield]
"name"
).@
where AssignmentOperator is @=
NOTE When an assignment occurs within strict mode code, it is an runtime error if lref in step 1.f.of the first algorithm or step 9 of the second algorithm it is an unresolvable reference. If it is, a ReferenceError exception is thrown. The LeftHandSide also may not be a reference to a data property with the attribute value {[[Writable]]:false}, to an accessor property with the attribute value {[[Set]]:undefined}, nor to a non-existent property of an object for which the IsExtensible predicate returns the value false. In these cases a TypeError exception is thrown.
In certain circumstances when processing the production AssignmentExpression
: LeftHandSideExpression =
AssignmentExpression the following grammar is used to refine the interpretation of LeftHandSideExpression.
{
}
{
AssignmentPropertyList[?Yield] }
{
AssignmentPropertyList[?Yield] ,
}
[
Elisionopt AssignmentRestElement[?Yield]opt ]
[
AssignmentElementList[?Yield] ]
[
AssignmentElementList[?Yield] ,
Elisionopt AssignmentRestElement[?Yield]opt ]
,
AssignmentProperty[?Yield],
AssignmentElisionElement[?Yield]:
AssignmentElement[?Yield]...
DestructuringAssignmentTarget[?Yield]It is a Syntax Error if IsValidSimpleAssignmentTarget of IdentifierReference is false.
It is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.
It is a Syntax Error if LeftHandSideExpression is neither an ObjectLiteral nor an ArrayLiteral and IsValidSimpleAssignmentTarget(LeftHandSideExpression) is false.
with parameter value
{
}
{
AssignmentPropertyList }
{
AssignmentPropertyList ,
}
[
]
[
Elision ]
[
Elisionopt AssignmentRestElement ]
[
AssignmentElementList ]
[
AssignmentElementList ,
Elisionopt AssignmentRestElementopt ]
,
AssignmentProperty"name"
).:
AssignmentElementwith parameters iteratorRecord
,
AssignmentElisionElement,
,
AssignmentElement[Yield] : DestructuringAssignmentTarget Initializeropt
"name"
).NOTE Left to right evaluation order is maintained by evaluating a DestructuringAssignmentTarget that is not a destructuring pattern prior to accessing the iterator or evaluating the Initializer.
AssignmentRestElement[Yield] : ...
DestructuringAssignmentTarget
with parameters value and propertyName
AssignmentElement[Yield] : DestructuringAssignmentTarget Initializeropt
"name"
)., )
,
AssignmentExpression[?In, ?Yield]See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 14.1.11, 14.4.9, 14.5.8.
,
AssignmentExpressionSee also: 12.1.3, 12.2.1.5, 12.2.10.3, 12.3.1.5, 12.4.3, 12.5.3, 12.6.2, 12.7.2, 12.8.2, 12.9.2, 12.10.2, 12.11.2, 12.12.2, 12.13.2, 12.14.3.
,
AssignmentExpression,
AssignmentExpressionNOTE GetValue must be called even though its value is not used because it may have observable side-effects.
With argument labelSet.
See also: 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
With argument labelSet.
See also: 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
With arguments iterationSet and labelSet.
See also: 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
See also: 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
See also: 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
With argument labelSet.
See also: 13.7.2.6, 13.7.3.6, 13.7.4.7, 13.7.5.11, 13.13.14.
NOTE A BreakableStatement is one that can be exited via an unlabelled BreakStatement.
{
StatementList[?Yield, ?Return]opt }
{
StatementList }
It is a Syntax Error if the LexicallyDeclaredNames of StatementList contains any duplicate entries.
It is a Syntax Error if any element of the LexicallyDeclaredNames of StatementList also occurs in the VarDeclaredNames of StatementList.
With argument labelSet.
See also: 13.1.1, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
{
}
With argument labelSet.
See also: 13.1.2, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
{
}
With arguments iterationSet and labelSet.
See also: 13.1.3, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
{
}
See also: 13.12.5, 13.13.6, 14.1.13, 14.2.10, 15.1.3, 15.2.1.11.
{
}
See also: 13.12.6, 13.13.7, 14.1.14, 14.2.11, 15.1.4, 15.2.1.12, 15.2.3.8.
See also: 13.13.8.
NOTE At the top level of a function, or script, function declarations are treated like var declarations rather than like lexical declarations.
See also: 13.13.9.
{
}
See also: 13.13.10.
{
}
NOTE At the top level of a function or script, inner function declarations are treated like var declarations.
See also: 13.13.11.
{
}
See also: 13.1.5, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
{
}
See also: 13.1.6, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
{
}
{
}
{
StatementList }
NOTE 1 No matter how control leaves the Block the LexicalEnvironment is always restored to its former state.
NOTE 2 The value of a StatementList is the value of the last value
producing item in the StatementList. For example, the following calls to the eval
function all return the value 1:
eval("1;;;;;")
eval("1;{}")
eval("1;var a;")
NOTE When a Block or CaseBlock production is evaluated a new declarative Environment Record is created and bindings for each block scoped variable, constant, function, generator function, or class declared in the block are instantiated in the Environment Record.
BlockDeclarationInstantiation is performed as follows using arguments code and env. code is the grammar production corresponding to the body of the block. env is the declarative Environment Record in which bindings are to be created.
NOTE let
and const
declarations define variables that are scoped to
the running execution context’s LexicalEnvironment. The variables are created when their containing Lexical Environment is instantiated but may not be accessed in any way until the
variable’s LexicalBinding is evaluated. A variable defined by a LexicalBinding with an Initializer is assigned the value of its Initializer’s AssignmentExpression when
the LexicalBinding is evaluated, not when the variable is created. If a LexicalBinding in a let
declaration does not have an Initializer
the variable is assigned the value undefined when the LexicalBinding is evaluated.
;
let
const
,
LexicalBinding[?In, ?Yield];
"let"
.It is a Syntax Error if Initializer is not present and IsConstantDeclaration of the LexicalDeclaration containing this production is true.
See also: 12.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
;
,
LexicalBindingSee also: 14.1.10, 14.4.8, 14.5.7, 15.2.3.7.
;
let
const
;
,
LexicalBindingNOTE A static semantics rule ensures that this form of LexicalBinding
never occurs in a const
declaration.
"name"
).NOTE A var
statement declares variables that are scoped to the running execution context’s VariableEnvironment. Var variables are created when their containing Lexical Environment is instantiated and are initialized to undefined when
created. Within the scope of any VariableEnvironment a common BindingIdentifier may appear in more than one VariableDeclaration but those
declarations collective define only one variable. A variable defined by a VariableDeclaration
with an Initializer is assigned the value of its Initializer’s AssignmentExpression when the VariableDeclaration is executed, not when the variable is created.
var
VariableDeclarationList[In, ?Yield] ;
,
VariableDeclaration[?In, ?Yield]See also: 12.1.2, 13.3.1.2, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
,
VariableDeclarationSee also: 13.1.5, 13.2.11, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
var
VariableDeclarationList ;
See also: 13.1.6, 13.2.12, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
,
VariableDeclarationvar
VariableDeclarationList ;
,
VariableDeclaration"name"
).NOTE If a VariableDeclaration is nested within a with statement and the BindingIdentifier in the VariableDeclaration is the same as a property name of the binding object of the with statement’s object Environment Record, then step 7 will assign value to the property instead of assigning to the VariableEnvironment binding of the Identifier.
{
}
{
BindingPropertyList[?Yield] }
{
BindingPropertyList[?Yield] ,
}
[
Elisionopt BindingRestElement[?Yield]opt ]
[
BindingElementList[?Yield] ]
[
BindingElementList[?Yield] ,
Elisionopt BindingRestElement[?Yield]opt ]
,
BindingProperty[?Yield],
BindingElisionElement[?Yield]:
BindingElement[?Yield]...
BindingIdentifier[?Yield]See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
{
}
[
Elisionopt ]
[
Elisionopt BindingRestElement ]
[
BindingElementList ,
Elisionopt ]
[
BindingElementList ,
Elisionopt BindingRestElement ]
,
BindingProperty,
BindingElisionElement:
BindingElement{
}
[
Elisionopt ]
[
Elisionopt BindingRestElement ]
[
BindingElementList ,
Elisionopt ]
[
BindingElementList ,
Elisionopt BindingRestElement ]
,
BindingProperty,
BindingElisionElement:
BindingElementWith parameters value and environment.
NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to deal with the possibility of multiple parameters with the same name.
{
}
,
BindingProperty:
BindingElementWith parameters iteratorRecord, and environment.
NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to deal with the possibility of multiple parameters with the same name.
[
]
[
Elision ]
[
Elisionopt BindingRestElement ]
[
BindingElementList ]
[
BindingElementList ,
]
[
BindingElementList ,
Elision ]
[
BindingElementList ,
Elisionopt BindingRestElement ]
,
BindingElisionElement"name"
)....
BindingIdentifierWith parameters value, environment, and propertyName.
NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to deal with the possibility of multiple parameters with the same name.
"name"
).;
{
, function
, class
, let [
}] Expression[In, ?Yield] ;
NOTE An ExpressionStatement cannot start with a U+007B (LEFT CURLY
BRACKET) because that might make it ambiguous with a Block. Also, an ExpressionStatement cannot start with the function
or class
keywords because
that would make it ambiguous with a FunctionDeclaration, a GeneratorDeclaration, or a ClassDeclaration. An ExpressionStatement cannot start with the two token sequence let [
because that would make
it ambiguous with a let
LexicalDeclaration whose first LexicalBinding was an ArrayBindingPattern.
;
if
Statementif
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return] else
Statement[?Yield, ?Return]if
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return]Each else
for which the choice of associated if
is ambiguous shall be associated with the
nearest possible if that would otherwise have no corresponding else
.
if
(
Expression )
Statement else
Statementif
(
Expression )
StatementNOTE It is only necessary to apply this rule if the extension specified in B.3.2 is implemented.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
if
(
Expression )
Statement else
Statementif
(
Expression )
StatementWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
if
(
Expression )
Statement else
Statementif
(
Expression )
StatementWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
if
(
Expression )
Statement else
Statementif
(
Expression )
StatementSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
if
(
Expression )
Statement else
Statementif
(
Expression )
StatementSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
if
(
Expression )
Statement else
Statementif
(
Expression )
Statementif
(
Expression )
Statement else
Statementif
(
Expression )
Statementdo
Statement[?Yield, ?Return] while
(
Expression[In, ?Yield] )
;
while
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
[lookahead ∉ {let [
}] Expression[?Yield]opt ;
Expression[In, ?Yield]opt ;
Expression[In, ?Yield]opt )
Statement[?Yield, ?Return]for
(
var
VariableDeclarationList[?Yield] ;
Expression[In, ?Yield]opt ;
Expression[In, ?Yield]opt )
Statement[?Yield, ?Return]for
(
LexicalDeclaration[?Yield] Expression[In, ?Yield]opt ;
Expression[In, ?Yield]opt )
Statement[?Yield, ?Return]for
(
[lookahead ∉ {let [
}] LeftHandSideExpression[?Yield] in
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
var
ForBinding[?Yield] in
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
ForDeclaration[?Yield] in
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
[lookahead ≠ let ] LeftHandSideExpression[?Yield] of
AssignmentExpression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
var
ForBinding[?Yield] of
AssignmentExpression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
ForDeclaration[?Yield] of
AssignmentExpression[In, ?Yield] )
Statement[?Yield, ?Return]do
Statement while
(
Expression )
;
while
(
Expression )
Statementfor
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
Statementfor
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementNOTE It is only necessary to apply this rule if the extension specified in B.3.2 is implemented.
The abstract operation LoopContinues with arguments completion and labelSet is defined by the following steps:
NOTE Within the Statement part of an IterationStatement a ContinueStatement may be used to begin a new iteration.
do
-while
StatementWith argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
do
Statement while
(
Expression )
;
With argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
do
Statement while
(
Expression )
;
With arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
do
Statement while
(
Expression )
;
See also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
do
Statement while
(
Expression )
;
See also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
do
Statement while
(
Expression )
;
With argument labelSet.
See also: 13.1.7, 13.7.3.6, 13.7.4.7, 13.7.5.11, 13.13.14.
do
Statement while
(
Expression )
;
while
StatementWith argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
while
(
Expression )
StatementWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
while
(
Expression )
StatementWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
while
(
Expression )
StatementSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
while
(
Expression )
StatementSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
while
(
Expression )
StatementWith argument labelSet.
See also: 13.1.7, 13.7.2.6, 13.7.4.7, 13.7.5.11, 13.13.14.
while
(
Expression )
Statementfor
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementIt is a Syntax Error if any element of the BoundNames of LexicalDeclaration also occurs in the VarDeclaredNames of Statement.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
for
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
for
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
for
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
for
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
for
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementWith argument labelSet.
See also: 13.1.7, 13.7.2.6, 13.7.3.6, 13.7.5.11, 13.13.14.
for
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
StatementThe abstract operation ForBodyEvaluation with arguments test, increment, stmt, perIterationBindings, and labelSet is performed as follows:
The abstract operation CreatePerIterationEnvironment with argument perIterationBindings is performed as follows:
for
-in
and
for
-of
Statementsfor
(
LeftHandSideExpression in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
StatementIt is a Syntax Error if LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression cannot be parsed with no tokens left over using AssignmentPattern as the goal symbol.
If LeftHandSideExpression is either an ObjectLiteral or an ArrayLiteral and if the lexical token sequence matched by LeftHandSideExpression can be parsed with no tokens left over using AssignmentPattern as the goal symbol then the following rules are not applied. Instead, the Early Error rules for AssignmentPattern are used.
It is a Syntax Error if IsValidSimpleAssignmentTarget of LeftHandSideExpression is false.
It is a Syntax Error if the LeftHandSideExpression is CoverParenthesizedExpressionAndArrowParameterList :
(
Expression )
and Expression derives a production that would produce a Syntax Error according to these rules if that
production is substituted for LeftHandSideExpression. This rule is recursively applied.
NOTE The last rule means that the other rules are applied even if parentheses surround Expression.
for
(
ForDeclaration in
Expression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementIt is a Syntax Error if the BoundNames of ForDeclaration contains "let"
.
It is a Syntax Error if any element of the BoundNames of ForDeclaration also occurs in the VarDeclaredNames of Statement.
It is a Syntax Error if the BoundNames of ForDeclaration contains any duplicate entries.
See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.11.2, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
for
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
for
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.8.2, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
for
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementSee also: 12.3.1.3.
See also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
for
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
for
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementWith arguments value and environment.
NOTE undefined is passed for environment to indicate that a PutValue operation should be used to assign the initialization value. This is the case for
var
statements and the formal parameter lists of some non-strict functions (see 9.2.12). In those cases a lexical binding is hoisted and
preinitialized prior to evaluation of its initializer.
With argument environment.
With argument labelSet.
See also: 13.1.7, 13.7.2.6, 13.7.3.6, 13.7.4.7, 13.13.14.
for
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
StatementThe abstract operation ForIn/OfHeadEvaluation is called with arguments TDZnames, expr, and iterationKind. The value of iterationKind is either enumerate or iterate.
The abstract operation ForIn/OfBodyEvaluation is called with arguments lhs, stmt, iterator, lhsKind, and labelSet. The value of lhsKind is either assignment, varBinding or lexicalBinding.
continue
Statementcontinue
;
continue
[no LineTerminator here] LabelIdentifier[?Yield] ;
ContinueStatement : continue
;
continue
LabelIdentifier ;
It is a Syntax Error if this production is not nested, directly or indirectly (but not crossing function boundaries), within an IterationStatement.
With arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.11.4, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
continue
;
continue
LabelIdentifier ;
continue
;
continue
LabelIdentifier ;
break
Statementbreak
;
break
[no LineTerminator here] LabelIdentifier[?Yield] ;
break
;
It is a Syntax Error if this production is not nested, directly or indirectly (but not crossing function boundaries), within an IterationStatement or a SwitchStatement.
With argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.11.3, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
break
;
break
LabelIdentifier ;
break
;
break
LabelIdentifier ;
return
Statementreturn
;
return
[no LineTerminator here] Expression[In, ?Yield] ;
NOTE A return
statement causes a function to cease execution and return a value to
the caller. If Expression is omitted, the return value is undefined. Otherwise, the return
value is the value of Expression.
return
;
return
Expression ;
with
Statementwith
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return]NOTE The with
statement adds an object Environment Record for a computed object to the lexical environment of the running execution
context. It then executes a statement using this augmented lexical
environment. Finally, it restores the original lexical environment.
with
(
Expression )
StatementNOTE It is only necessary to apply the second rule if the extension specified in B.3.2 is implemented.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.12.2, 13.13.2, 13.15.2, 15.2.1.2.
with
(
Expression )
StatementWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.12.3, 13.13.3, 13.15.3, 15.2.1.3.
with
(
Expression )
StatementWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.12.4, 13.13.4,13.15.4, 15.2.1.4.
with
(
Expression )
StatementSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
with
(
Expression )
StatementSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
with
(
Expression )
Statementwith
(
Expression )
StatementNOTE No matter how control leaves the embedded Statement, whether normally or by some form of abrupt completion or exception, the LexicalEnvironment is always restored to its former state.
switch
Statementswitch
(
Expression[In, ?Yield] )
CaseBlock[?Yield, ?Return]{
CaseClauses[?Yield, ?Return]opt }
{
CaseClauses[?Yield, ?Return]opt DefaultClause[?Yield, ?Return] CaseClauses[?Yield, ?Return]opt }
case
Expression[In, ?Yield] :
StatementList[?Yield, ?Return]optdefault
:
StatementList[?Yield, ?Return]opt{
CaseClauses }
It is a Syntax Error if the LexicallyDeclaredNames of CaseClauses contains any duplicate entries.
It is a Syntax Error if any element of the LexicallyDeclaredNames of CaseClauses also occurs in the VarDeclaredNames of CaseClauses.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.13.2, 13.15.2, 15.2.1.2.
switch
(
Expression )
CaseBlock{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.13.3, 13.15.3, 15.2.1.3.
switch
(
Expression )
CaseBlock{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.13.4,13.15.4, 15.2.1.4.
switch
(
Expression )
CaseBlock{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptSee also: 13.2.5, 13.13.6, 14.1.13, 14.2.10, 15.1.3, 15.2.1.11.
{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptSee also: 13.2.6, 13.13.7, 14.1.14, 14.2.11, 15.1.4, 15.2.1.12, 15.2.3.8.
{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
switch
(
Expression )
CaseBlock{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
switch
(
Expression )
CaseBlock{
}
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptdefault
:
StatementListoptWith argument input.
{
}
{
CaseClauses }
{
CaseClausesopt DefaultClause CaseClausesopt }
case
Expression :
StatementListoptNOTE CaseSelectorEvaluation does not execute the associated StatementList. It simply evaluates the Expression and returns the value, which the CaseBlock algorithm uses to determine which StatementList to start executing.
switch
(
Expression )
CaseBlockNOTE No matter how control leaves the SwitchStatement the LexicalEnvironment is always restored to its former state.
case
Expression :
case
Expression :
StatementListdefault
:
default
:
StatementList:
LabelledItem[?Yield, ?Return]NOTE A Statement may be prefixed by a label. Labelled statements are
only used in conjunction with labelled break
and continue
statements. ECMAScript has no
goto
statement. A Statement can be part of a LabelledStatement, which itself can be part of a LabelledStatement, and so on.
The labels introduced this way are collectively referred to as the “current label set” when describing the
semantics of individual statements. A LabelledStatement has no semantic meaning other than the
introduction of a label to a label set.
NOTE An alternative definition for this rule is provided in B.3.2.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.15.2, 15.2.1.2.
:
LabelledItemWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.15.3, 15.2.1.3.
:
LabelledItemWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.15.4, 15.2.1.4.
:
LabelledItemThe abstract operation IsLabelledFunction with argument stmt performs the following steps:
See also: 13.2.5, 13.12.5, 14.1.13, 14.2.10, 15.1.3, 15.2.1.11.
:
LabelledItemSee also: 13.2.6, 13.12.6, 14.1.14, 14.2.11, 15.1.4, 15.2.1.12, 15.2.3.8.
:
LabelledItemSee also: 13.2.7.
:
LabelledItemSee also: 13.2.8.
:
LabelledItemSee also: 13.2.9.
:
LabelledItemSee also: 13.2.10.
:
LabelledItemSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.15.5, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
:
LabelledItemSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.15.6, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
:
LabelledItemWith argument labelSet.
See also: 13.1.7, 13.7.2.6, 13.7.3.6, 13.7.4.7, 13.7.5.11.
:
LabelledItemLabelledItem : FunctionDeclaration
:
LabelledItemthrow
Statementthrow
[no LineTerminator here] Expression[In, ?Yield] ;
throw
Expression ;
try
Statementtry
Block[?Yield, ?Return] Catch[?Yield, ?Return]try
Block[?Yield, ?Return] Finally[?Yield, ?Return]try
Block[?Yield, ?Return] Catch[?Yield, ?Return] Finally[?Yield, ?Return]catch
(
CatchParameter[?Yield] )
Block[?Yield, ?Return]finally
Block[?Yield, ?Return]NOTE The try
statement encloses a block of code in which an exceptional condition
can occur, such as a runtime error or a throw
statement. The catch
clause provides the
exception-handling code. When a catch clause catches an exception, its CatchParameter is bound to
that exception.
catch
(
CatchParameter )
BlockIt is a Syntax Error if BoundNames of CatchParameter contains any duplicate elements.
It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the LexicallyDeclaredNames of Block.
It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the VarDeclaredNames of Block.
NOTE An alternative static semantics for this production is given in B.3.5.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 15.2.1.2.
try
Block Catchtry
Block Finallytry
Block Catch Finallycatch
(
CatchParameter )
BlockWith argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 15.2.1.3.
try
Block Catchtry
Block Finallytry
Block Catch Finallycatch
(
CatchParameter )
BlockWith arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4, 15.2.1.4.
try
Block Catchtry
Block Finallytry
Block Catch Finallycatch
(
CatchParameter )
BlockSee also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 14.1.15, 14.2.12, 15.1.5, 15.2.1.13.
try
Block Catchtry
Block Finallytry
Block Catch Finallycatch
(
CatchParameter )
BlockSee also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 14.1.16, 14.2.13, 15.1.6, 15.2.1.14.
try
Block Catchtry
Block Finallytry
Block Catch Finallycatch
(
CatchParameter )
Blockwith parameter thrownValue
catch
(
CatchParameter )
BlockNOTE No matter how control leaves the Block the LexicalEnvironment is always restored to its former state.
try
Block Catchtry
Block Finallytry
Block Catch FinallyNOTE Evaluating the DebuggerStatement production may allow an implementation to cause a breakpoint when run under a debugger. If a debugger is not present or active this statement has no observable effect.
debugger
;
function
BindingIdentifier[?Yield] (
FormalParameters )
{
FunctionBody }
function
(
FormalParameters )
{
FunctionBody }
function
BindingIdentifieropt (
FormalParameters )
{
FunctionBody }
,
FunctionRestParameter[?Yield],
FormalParameter[?Yield]A Directive Prologue is the longest sequence of ExpressionStatement productions occurring as the initial StatementListItem or ModuleItem productions of a FunctionBody, a ScriptBody, or a ModuleBody and where each ExpressionStatement in the sequence consists entirely of a StringLiteral token followed by a semicolon. The semicolon may appear explicitly or may be inserted by automatic semicolon insertion. A Directive Prologue may be an empty sequence.
A Use Strict Directive is an ExpressionStatement in a Directive Prologue whose StringLiteral is either the exact code unit sequences "use
strict"
or
'use
strict'
. A Use Strict Directive may not contain an EscapeSequence or LineContinuation.
A Directive Prologue may contain more than one Use Strict Directive. However, an implementation may issue a warning if this occurs.
NOTE The ExpressionStatement productions of a Directive Prologue are evaluated normally during evaluation of the containing production. Implementations may define implementation specific meanings for ExpressionStatement productions which are not a Use Strict Directive and which occur in a Directive Prologue. If an appropriate notification mechanism exists, an implementation should issue a warning if it encounters in a Directive Prologue an ExpressionStatement that is not a Use Strict Directive and which does not have a meaning defined by the implementation.
FunctionDeclaration : function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
FunctionDeclaration : function
(
FormalParameters )
{
FunctionBody }
FunctionExpression : function
BindingIdentifieropt (
FormalParameters )
{
FunctionBody
}
If the source code matching this production is strict code, the Early Error rules for StrictFormalParameters : FormalParameters are applied.
If the source code matching this production is strict code, it is a Syntax Error
if BindingIdentifier is the IdentifierName eval
or the
IdentifierName arguments
.
It is a Syntax Error if any element of the BoundNames of FormalParameters also occurs in the LexicallyDeclaredNames of FunctionBody.
It is a Syntax Error if FormalParameters Contains SuperProperty is true.
It is a Syntax Error if FunctionBody Contains SuperProperty is true.
It is a Syntax Error if FormalParameters Contains SuperCall is true.
It is a Syntax Error if FunctionBody Contains SuperCall is true.
NOTE 1 The LexicallyDeclaredNames of a FunctionBody does not include identifiers bound using var or function declarations.
It is a Syntax Error if BoundNames of FormalParameters contains any duplicate elements.
It is a Syntax Error if IsSimpleParameterList of FormalParameterList is false and BoundNames of FormalParameterList contains any duplicate elements.
NOTE 2 Multiple occurrences of the same BindingIdentifier in a FormalParameterList is only allowed for functions and generator functions which have simple parameter lists and which are not defined in strict mode code.
It is a Syntax Error if the LexicallyDeclaredNames of FunctionStatementList contains any duplicate entries.
It is a Syntax Error if any element of the LexicallyDeclaredNames of FunctionStatementList also occurs in the VarDeclaredNames of FunctionStatementList.
It is a Syntax Error if ContainsDuplicateLabels of FunctionStatementList with argument « » is true.
It is a Syntax Error if ContainsUndefinedBreakTarget of FunctionStatementList with argument « » is true.
It is a Syntax Error if ContainsUndefinedContinueTarget of FunctionStatementList with arguments « » and « » is true.
See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
function
(
FormalParameters )
{
FunctionBody }
"*default*"
».NOTE "*default*"
is used within this specification as a synthetic name for
hoistable anonymous functions that are defined using export declarations.
,
FunctionRestParameter,
FormalParameterWith parameter symbol.
See also: 5.3, 12.2.6.3, 12.3.1.1, 14.2.3, 14.4.4, 14.5.4
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
FunctionDeclaration : function
(
FormalParameters )
{
FunctionBody }
FunctionExpression : function
BindingIdentifieropt (
FormalParameters )
{
FunctionBody
}
NOTE Static semantic rules that depend upon substructure generally do not look into function definitions.
,
FunctionRestParameter,
FormalParameter,
FunctionRestParameterNOTE The ExpectedArgumentCount of a FormalParameterList is the number of FormalParameters to the left of either the rest parameter or the first FormalParameter with an Initializer. A FormalParameter without an initializer is allowed after the first parameter with an initializer but such parameters are considered to be optional with undefined as their default value.
,
FormalParameter,
FunctionRestParameter,
FormalParameterSee also: 12.2.1.2, 14.2.7, 14.4.7, 14.5.6.
function
(
FormalParameters )
{
FunctionBody }
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
The abstract operation IsAnonymousFunctionDefinition determines if its argument is a function definition that does not bind a name. The argument production is the result of parsing an AssignmentExpression or Initializer. The following steps are taken:
See also: 13.3.1.3, 14.4.8, 14.5.7, 15.2.3.7.
FunctionDeclaration : function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
FunctionDeclaration : function
(
FormalParameters )
{
FunctionBody }
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.4.9, 14.5.8.
function
(
FormalParameters )
{
FunctionBody }
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
,
FunctionRestParameter,
FormalParameterSee also: 13.2.5, 13.12.5, 13.13.6, 14.2.10, 15.1.3, 15.2.1.11.
See also: 13.2.6, 13.12.6, 13.13.7, 14.2.11, 15.1.4, 15.2.1.12, 15.2.3.8.
See also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.2.12, 15.1.5, 15.2.1.13.
See also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.2.13, 15.1.6, 15.2.1.14.
With parameter functionObject.
With parameters iteratorRecord and environment.
NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to deal with the possibility of multiple parameters with the same name.
,
FunctionRestParameter,
FormalParameterThe new Environment Record created in step 6 is only used if the BindElement’s Initializer contains a direct eval.
With parameter scope.
See also: 14.4.12.
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
function
(
FormalParameters )
{
FunctionBody }
"default"
).NOTE An anonymous FunctionDeclaration can only occur as part of an
export default
declaration.
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
NOTE 1 An alternative semantics is provided in B.3.3.
function
(
FormalParameters )
{
FunctionBody }
function
(
FormalParameters )
{
FunctionBody }
function
BindingIdentifier (
FormalParameters )
{
FunctionBody }
NOTE 2 The BindingIdentifier in a FunctionExpression can be referenced from inside the FunctionExpression's FunctionBody to allow the function to call itself recursively. However, unlike in a FunctionDeclaration, the BindingIdentifier in a FunctionExpression cannot be referenced from and does not affect the scope enclosing the FunctionExpression.
NOTE 3 A prototype
property is automatically created for every function defined
using a FunctionDeclaration or FunctionExpression, to allow for the
possibility that the function will be used as a constructor.
=>
ConciseBody[?In]{
FunctionBody }
When the production
ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]
is recognized the following grammar is used to refine the interpretation of CoverParenthesizedExpressionAndArrowParameterList :
(
StrictFormalParameters[?Yield] )
=>
ConciseBodyIt is a Syntax Error if ArrowParameters Contains YieldExpression is true.
It is a Syntax Error if ConciseBody Contains YieldExpression is true.
It is a Syntax Error if any element of the BoundNames of ArrowParameters also occurs in the LexicallyDeclaredNames of ConciseBody.
ArrowParameters[Yield] : CoverParenthesizedExpressionAndArrowParameterList[?Yield]
If the [Yield] grammar parameter is present on ArrowParameters, it is a Syntax Error if the lexical token sequence matched by CoverParenthesizedExpressionAndArrowParameterList[?Yield] cannot be parsed with no tokens left over using ArrowFormalParameters[Yield] as the goal symbol.
If the [Yield] grammar parameter is not present on ArrowParameters, it is a Syntax Error if the lexical token sequence matched by CoverParenthesizedExpressionAndArrowParameterList[?Yield] cannot be parsed with no tokens left over using ArrowFormalParameters as the goal symbol.
All early errors rules for ArrowFormalParameters and its derived productions also apply to CoveredFormalsList of CoverParenthesizedExpressionAndArrowParameterList[?Yield].
See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.4.2, 14.5.2, 15.2.2.2, 15.2.3.2.
With parameter symbol.
See also: 5.3, 12.2.6.3, 12.3.1.1, 14.1.4, 14.4.4, 14.5.4
=>
ConciseBodysuper
or
this
, return false.NOTE Normally, Contains does not look inside
most function forms However, Contains is used to detect
new.target
, this
, and super
usage within an ArrowFunction.
ArrowParameters : CoverParenthesizedExpressionAndArrowParameterList
See also: 12.2.1.2, 14.1.8, 14.4.7, 14.5.6.
=>
ConciseBody(
Expression )
(
)
(
...
BindingIdentifier )
(
Expression ,
...
BindingIdentifier )
See also: 13.2.5, 13.12.5, 13.13.6, 14.1.13, 15.1.3, 15.2.1.11.
See also: 13.2.6, 13.12.6, 13.13.7, 14.1.14, 15.1.4, 15.2.1.12, 15.2.3.8.
See also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 15.1.5, 15.2.1.13.
See also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 15.1.6, 15.2.1.14.
With parameters iteratorRecord and environment.
NOTE When undefined is passed for environment it indicates that a PutValue operation should be used to assign the initialization value. This is the case for formal parameter lists of non-strict functions. In that case the formal parameter bindings are preinitialized in order to deal with the possibility of multiple parameters with the same name.
With parameter functionObject.
=>
ConciseBodyNOTE An ArrowFunction does not define local bindings for
arguments
, super
, this
, or new.target
. Any reference to
arguments
, super
, this
, or new.target
within an ArrowFunction must resolve to a binding in a lexically enclosing environment. Typically this will be the
Function Environment of an immediately enclosing function. Even though an ArrowFunction may
contain references to super
, the function object created in step 4 is not made into a method by performing MakeMethod. An ArrowFunction that references super
is
always contained within a non-ArrowFunction and the necessary state to implement
super
is accessible via the scope that is captured by the function object of the ArrowFunction.
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName[?Yield] (
)
{
FunctionBody }
set
PropertyName[?Yield] (
PropertySetParameterList )
{
FunctionBody }
(
StrictFormalParameters )
{
FunctionBody }
It is a Syntax Error if any element of the BoundNames of StrictFormalParameters also occurs in the LexicallyDeclaredNames of FunctionBody.
set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
It is a Syntax Error if BoundNames of PropertySetParameterList contains any duplicate elements.
It is a Syntax Error if any element of the BoundNames of PropertySetParameterList also occurs in the LexicallyDeclaredNames of FunctionBody.
With parameter symbol.
See also: 12.2.6.2, 14.4.3, 14.5.5.
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName (
)
{
FunctionBody }
set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName (
)
{
FunctionBody }
set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
See also: 14.4.6.
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName (
)
{
FunctionBody }
set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
See also: 12.2.6.6, 14.4.10, 14.5.12
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName (
)
{
FunctionBody }
set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName (
)
{
FunctionBody }
set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
With parameters object and optional parameter functionPrototype.
(
StrictFormalParameters )
{
FunctionBody }
With parameters object and enumerable.
See also: 12.2.6.9, 14.4.13, B.3.1
(
StrictFormalParameters )
{
FunctionBody }
See 14.4.
get
PropertyName (
)
{
FunctionBody }
"get"
).set
PropertyName (
PropertySetParameterList )
{
FunctionBody }
"set"
).*
PropertyName[?Yield] (
StrictFormalParameters[Yield] )
{
GeneratorBody }
function
*
BindingIdentifier[?Yield] (
FormalParameters[Yield] )
{
GeneratorBody }
function
*
(
FormalParameters[Yield] )
{
GeneratorBody }
function
*
BindingIdentifier[Yield]opt (
FormalParameters[Yield] )
{
GeneratorBody }
yield
yield
[no LineTerminator here] AssignmentExpression[?In, Yield]yield
[no LineTerminator here] *
AssignmentExpression[?In, Yield]NOTE 1 The syntactic context immediately following yield
requires use of the InputElementRegExpOrTemplateTail lexical goal.
NOTE 2 YieldExpression cannot be used within the FormalParameters of a generator function because any expressions that are part of FormalParameters are evaluated before the resulting generator object is in a resumable state.
NOTE 3 Abstract operations relating to generator objects are defined in 25.3.3.
*
PropertyName (
StrictFormalParameters )
{
GeneratorBody }
It is a Syntax Error if HasDirectSuper of GeneratorMethod is true.
It is a Syntax Error if StrictFormalParameters Contains YieldExpression is true.
It is a Syntax Error if any element of the BoundNames of StrictFormalParameters also occurs in the LexicallyDeclaredNames of GeneratorBody.
function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
function
*
BindingIdentifieropt (
FormalParameters )
{
GeneratorBody }
GeneratorDeclaration : function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody
}
GeneratorExpression :
function
*
BindingIdentifieropt (
FormalParameters )
{
GeneratorBody }
If the source code matching this production is strict code, the Early Error rules for StrictFormalParameters : FormalParameters are applied.
If the source code matching this production is strict code, it is a Syntax Error
if BindingIdentifier is the IdentifierName eval
or the
IdentifierName arguments
.
It is a Syntax Error if any element of the BoundNames of FormalParameters also occurs in the LexicallyDeclaredNames of GeneratorBody.
It is a Syntax Error if FormalParameters Contains YieldExpression is true.
It is a Syntax Error if FormalParameters Contains SuperProperty is true.
It is a Syntax Error if GeneratorBody Contains SuperProperty is true.
See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.5.2, 15.2.2.2, 15.2.3.2.
function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
function
*
(
FormalParameters )
{
GeneratorBody }
"*default*"
».NOTE "*default*"
is used within this specification as a synthetic name for
hoistable anonymous functions that are defined using export declarations.
With parameter symbol.
See also: 12.2.6.2, 14.3.2, 14.5.5.
*
PropertyName (
StrictFormalParameters )
{
GeneratorBody }
With parameter symbol.
See also: 5.3, 12.2.6.3, 12.3.1.1, 14.1.4, 14.2.3, 14.5.4
GeneratorDeclaration : function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody
}GeneratorDeclaration
:
function
*
(
FormalParameters )
{
GeneratorBody }
function
*
BindingIdentifieropt (
FormalParameters )
{
GeneratorBody }
NOTE Static semantic rules that depend upon substructure generally do not look into function definitions.
*
PropertyName (
StrictFormalParameters )
{
GeneratorBody }
See also: 14.3.5.
*
PropertyName (
StrictFormalParameters )
{
GeneratorBody }
GeneratorDeclaration : function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody
}
GeneratorDeclaration :
function
*
(
FormalParameters )
{
GeneratorBody }
GeneratorExpression : function
*
(
FormalParameters )
{
GeneratorBody }
GeneratorExpression : function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
See also: 12.2.1.2, 14.1.8, 14.2.7, 14.5.6.
function
*
(
FormalParameters )
{
GeneratorBody }
function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
See also: 13.3.1.3, 14.1.10, 14.5.7, 15.2.3.7.
GeneratorDeclaration : function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody
}GeneratorDeclaration
:
function
*
(
FormalParameters )
{
GeneratorBody }
See also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.5.8.
function
*
(
FormalParameters )
{
GeneratorBody }
function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
See also: 12.2.6.6, 14.3.6, 14.5.12
*
PropertyName (
StrictFormalParameters )
{
GeneratorBody }
With parameter functionObject.
"%GeneratorPrototype%"
, «[[GeneratorState]], [[GeneratorContext]]» ).NOTE If the generator was invoked using [[Call]], the this
binding will have
already been initialized in the normal manner. If the generator was invoked using [[Construct]], the this
bind is not initialized and any references to this
within the FunctionBody will
produce a ReferenceError exception.
With parameter scope.
See also: 14.1.19.
function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
function
*
(
FormalParameters )
{
GeneratorBody }
"default"
).NOTE An anonymous GeneratorDeclaration can only occur as part of an
export default
declaration.
With parameter object and enumerable.
See also: 12.2.6.9, 14.3.9, B.3.1
*
PropertyName (
StrictFormalParameters )
{
GeneratorBody }
function
*
(
FormalParameters )
{
GeneratorBody }
function
*
BindingIdentifier (
FormalParameters )
{
GeneratorBody }
NOTE The BindingIdentifier in a GeneratorExpression can be referenced from inside the GeneratorExpression's FunctionBody to allow the generator code to call itself recursively. However, unlike in a GeneratorDeclaration, the BindingIdentifier in a GeneratorExpression cannot be referenced from and does not affect the scope enclosing the GeneratorExpression.
yield
yield
AssignmentExpressionyield
*
AssignmentExpression"throw"
).throw
method are propagated. Normal completions
from an inner throw
method are processed similarly to an inner next
.throw
method, this throw is going to terminate
the yield*
loop. But first we need to give iterator a chance to clean up.yield*
protocol violation: iterator does not have a throw
method."return"
).class
BindingIdentifier[?Yield] ClassTail[?Yield]class
ClassTail[?Yield]class
BindingIdentifier[?Yield]opt ClassTail[?Yield]{
ClassBody[?Yield]opt }
extends
LeftHandSideExpression[?Yield]static
MethodDefinition[?Yield];
NOTE A ClassBody is always strict code.
{
ClassBody }
It is a Syntax Error if ClassHeritage is not present and the following algorithm evaluates to true:
It is a Syntax Error if PrototypePropertyNameList of ClassElementList contains more than one occurrence of "constructor"
.
It is a Syntax Error if PropName of MethodDefinition is not "constructor"
and HasDirectSuper of MethodDefinition is true.
It is a Syntax Error if PropName of MethodDefinition is "constructor"
and SpecialMethod of MethodDefinition is true.
static
MethodDefinition"prototype"
.See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 15.2.2.2, 15.2.3.2.
class
BindingIdentifier ClassTailclass
ClassTail"*default*"
».;
, return empty."constructor"
, return empty.;
, return empty."constructor"
, return empty.NOTE Early Error rules ensure that there is only one method definition named
"constructor"
and that it is not an accessor property or generator definition.
With parameter symbol.
See also: 5.3, 12.2.6.3, 12.3.1.1, 14.1.4, 14.2.3, 14.4.4
{
ClassBody }
NOTE Static semantic rules that depend upon substructure generally do not look into class bodies except for PropertyName productions.
With parameter symbol.
See also: 12.2.6.2, 14.3.2, 14.4.3.
static
MethodDefinition;
See also: 12.2.1.2, 14.1.8, 14.2.7, 14.4.7.
class
ClassTailclass
BindingIdentifier ClassTailSee also: 13.3.1.3, 14.1.10, 14.4.8, 15.2.3.7.
ClassDeclaration : class
BindingIdentifier ClassTail
class
ClassTailSee also: 12.2.1.3, 12.2.10.2, 12.3.1.2, 12.4.2, 12.5.2, 12.6.1, 12.7.1, 12.8.1, 12.9.1, 12.10.1, 12.11.1, 12.12.1, 12.13.1, 12.14.2, 12.15.1, 14.1.11, 14.4.9.
class
ClassTailclass
BindingIdentifier ClassTailstatic
MethodDefinition;
;
, return a new empty List."constructor"
,
return a new empty List.;
, return list."constructor"
,
return list.See also: 12.2.6.6, 14.3.6, 14.4.10
;
With parameter className.
{
ClassBodyopt }
"generator"
, throw a TypeError exception."prototype"
).constructor(... args){ super
(...args);}
using
the syntactic grammar with the goal symbol MethodDefinition.constructor(
){ }
using the syntactic grammar with the goal symbol MethodDefinition."derived"
."constructor"
,
F).class
BindingIdentifier ClassTail"name"
).class
ClassTailNOTE ClassDeclaration :
class
ClassTail only occurs as part of an ExportDeclaration and the setting of a name property and establishing its binding are handled as part
of the evaluation action for that production. See 15.2.3.11.
class
BindingIdentifier ClassTailNOTE 1 ClassDeclaration :
class
ClassTail only occurs as part of an ExportDeclaration and is never directly evaluated.
class
BindingIdentifieropt ClassTail"name"
).NOTE 2 If the class definition included a name
static method then that method is
not over-written with a name
data property for the class name.
The abstract operation IsInTailPosition with argument nonterminal performs the following steps:
NOTE Tail Position calls are only defined in strict mode code because of a common non-standard language extension (see 9.2.7) that enables observation of the chain of caller contexts.
With parameter nonterminal.
NOTE nonterminal is a parsed grammar production that represent a specific range of source text. When the following algorithms compare nonterminal to other grammar symbols they are testing whether the same source text was matched by both symbols.
FunctionStatementList : [empty]
StatementListItem : Declaration
:
{
}
:
return
;
:
FunctionDeclarationfor
(
LeftHandSideExpression in
Expression )
Statementfor
(
var
ForBinding in
Expression )
Statementfor
(
ForDeclaration in
Expression )
Statementfor
(
LeftHandSideExpression of
AssignmentExpression )
Statementfor
(
var
ForBinding of
AssignmentExpression )
Statementfor
(
ForDeclaration of
AssignmentExpression )
Statement:
{
}
if
(
Expression )
Statement else
StatementIfStatement : if
(
Expression )
Statement
do
Statement while
(
Expression )
;
while
(
Expression )
Statementfor
(
Expressionopt ;
Expressionopt ;
Expressionopt )
Statementfor
(
var
VariableDeclarationList ;
Expressionopt ;
Expressionopt )
Statementfor
(
LexicalDeclaration Expressionopt ;
Expressionopt )
Statement:
with
(
Expression )
Statement:
LabelledItemreturn
Expression ;
switch
(
Expression )
CaseBlock{
CaseClausesopt DefaultClause CaseClausesopt }
CaseClause : case
Expression :
StatementListopt
default
:
StatementListopttry
Block CatchTryStatement : try
Block Finally
try
Block Catch Finallycatch
(
CatchParameter )
BlockNOTE A potential tail position call that is immediately followed by return GetValue of the call result is also a possible tail position call. Function calls cannot return reference values, so such a GetValue operation will always returns the same value as the actual function call result.
=
AssignmentExpression:
BitwiseANDExpression &
EqualityExpression:
BitwiseXORExpression ^
BitwiseANDExpression:
BitwiseORExpression |
BitwiseXORExpression==
RelationalExpression!=
RelationalExpression===
RelationalExpression!==
RelationalExpression<
ShiftExpression>
ShiftExpression<=
ShiftExpression>=
ShiftExpressioninstanceof
ShiftExpressionin
ShiftExpression<<
AdditiveExpression>>
AdditiveExpression>>>
AdditiveExpression+
MultiplicativeExpression-
MultiplicativeExpressiondelete
UnaryExpressionvoid
UnaryExpressiontypeof
UnaryExpression++
UnaryExpression--
UnaryExpression+
UnaryExpression-
UnaryExpression~
UnaryExpression!
UnaryExpression++
--
[
Expression ]
.
IdentifierName:
new
NewExpression[
Expression ]
.
IdentifierNamenew
MemberExpression Argumentsthis
,
AssignmentExpression?
AssignmentExpression :
AssignmentExpression&&
BitwiseORExpression||
LogicalANDExpression(
Expression )
The abstract operation PrepareForTailCall performs the following steps:
A tail position call must either release any transient internal resources associated with the currently executing function execution context before invoking the target function or reuse those resources in support of the target function.
NOTE For example, a tail position call should only grow an implementation’s activation record stack by the amount that the size of the target function’s activation record exceeds the size of the calling function’s activation record. If the target function’s activation record is smaller, then the total size of the stack should decrease.
It is a Syntax Error if the LexicallyDeclaredNames of ScriptBody contains any duplicate entries.
It is a Syntax Error if any element of the LexicallyDeclaredNames of ScriptBody also occurs in the VarDeclaredNames of ScriptBody.
It is a Syntax Error if StatementList Contains super
unless the source code containing super
is eval code that is
being processed by a direct eval
that is contained in function code that is not the function code of an
ArrowFunction.
It is a Syntax Error if StatementList Contains NewTarget unless the source code containing NewTarget is eval code that is being processed by a direct eval
that is contained in
function code that is not the function code of an ArrowFunction.
It is a Syntax Error if ContainsDuplicateLabels of StatementList with argument « » is true.
It is a Syntax Error if ContainsUndefinedBreakTarget of StatementList with argument « » is true.
It is a Syntax Error if ContainsUndefinedContinueTarget of StatementList with arguments « » and « » is true.
See also: 13.2.5, 13.12.5, 13.13.6, 14.1.13, 14.2.10, 15.2.1.11.
NOTE At the top level of a Script, function declarations are treated like var declarations rather than like lexical declarations.
See also: 13.2.6, 13.12.6, 13.13.7, 14.1.14, 14.2.11, 15.2.1.12, 15.2.3.8.
See also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.2.1.13.
See also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.2.1.14.
With argument realm.
NOTE 1 When an execution context is established for evaluating scripts, declarations are instantiated in the current global environment. Each global binding declared in the code is instantiated.
GlobalDeclarationInstantiation is performed as follows using arguments script and env. script is the ScriptBody for which the execution context is being established. env is the global lexical environment in which bindings are to be created.
NOTE 2 Early errors specified in 15.1.1 prevent name conflicts between function/var declarations and let/const/class declarations as well as redeclaration of let/const/class bindings for declaration contained within a single Script. However, such conflicts and redeclarations that span more than one Script are detected as runtime errors during GlobalDeclarationInstantiation. If any such errors are detected, no bindings are instantiated for the script. However, if the global object is defined using Proxy exotic objects then the runtime tests for conflicting declarations may be unreliable resulting in an abrupt completion and some global declarations not being instantiated. If this occurs, the code for the Script is not evaluated.
Unlike explicit var or function declarations, properties that are directly created on the global object result in global bindings that may be shadowed by let/const/class declarations.
The job ScriptEvaluationJob with parameter sourceText parses, validates, and evaluates sourceText as a Script.
NOTE An implementation may parse a sourceText as a Script and analyze it for Early Error conditions prior to the execution of the ScriptEvaluationJob for that sourceText. However, the reporting of any errors must be deferred until the ScriptEvaluationJob is actually executed.
It is a Syntax Error if the LexicallyDeclaredNames of ModuleItemList contains any duplicate entries.
It is a Syntax Error if any element of the LexicallyDeclaredNames of ModuleItemList also occurs in the VarDeclaredNames of ModuleItemList.
It is a Syntax Error if the ExportedNames of ModuleItemList contains any duplicate entries.
It is a Syntax Error if any element of the ExportedBindings of ModuleItemList does not also occur in either the VarDeclaredNames of ModuleItemList, or the LexicallyDeclaredNames of ModuleItemList.
It is a Syntax Error if ModuleItemList Contains super
.
It is a Syntax Error if ModuleItemList Contains NewTarget
It is a Syntax Error if ContainsDuplicateLabels of ModuleItemList with argument « » is true.
It is a Syntax Error if ContainsUndefinedBreakTarget of ModuleItemList with argument « » is true.
It is a Syntax Error if ContainsUndefinedContinueTarget of ModuleItemList with arguments « » and « » is true.
NOTE The duplicate ExportedNames rule implies that multiple export default
ExportDeclaration items within a ModuleBody is a Syntax Error. Additional
error conditions relating to conflicting or duplicate declarations are checked during module linking prior to evaluation
of a Module. If any such errors are detected the Module is not
evaluated.
With argument labelSet.
See also: 13.1.1, 13.2.2, 13.6.2, 13.7.2.1, 13.7.3.1, 13.7.4.2, 13.7.5.3, 13.11.2, 13.12.2, 13.13.2, 13.15.2.
With argument labelSet.
See also: 13.1.2, 13.2.3, 13.6.3, 13.7.2.2, 13.7.3.2, 13.7.4.3, 13.7.5.4, 13.9.2, 13.11.3, 13.12.3, 13.13.3, 13.15.3.
With arguments iterationSet and labelSet.
See also: 13.1.3, 13.2.4, 13.6.4, 13.7.2.3, 13.7.3.3, 13.7.4.4, 13.7.5.5, 13.8.2, 13.11.4, 13.12.4, 13.13.4, 13.15.4.
See also: 15.2.3.3.
NOTE ExportedBindings are the locally bound names that are explicitly associated with a Module’s ExportedNames.
See also: 15.2.3.4.
NOTE ExportedNames are the externally visible names that a Module explicitly maps to one of its local name bindings.
See also: 15.2.3.5.
See also: 15.2.2.3.
The abstract operation ImportedLocalNames with argument importEntries creates a List of all of the local name bindings defined by a List of ImportEntry Records (see Table 39). ImportedLocalNames performs the following steps:
See also: 13.2.5, 13.12.5, 13.13.6, 14.1.13, 14.2.10, 15.1.3.
NOTE 1 The LexicallyDeclaredNames of a Module includes the names of all of its imported bindings.
export
VariableStatement, return a new empty List.NOTE 2 At the top level of a Module, function declarations are treated like lexical declarations rather than like var declarations.
See also: 13.2.6, 13.12.6, 13.13.7, 14.1.14, 14.2.11, 15.1.4, 15.2.3.8.
See also: 13.1.5, 13.2.11, 13.3.2.2, 13.6.5, 13.7.2.4, 13.7.3.4, 13.7.4.5, 13.7.5.7, 13.11.5, 13.12.7, 13.13.12, 13.15.5, 14.1.15, 14.2.12, 15.1.5.
ModuleItemList : ModuleItemList ModuleItem
export
VariableStatement, return BoundNames of
ExportDeclaration.See also: 13.1.6, 13.2.12, 13.3.2.3, 13.6.6, 13.7.2.5, 13.7.3.5, 13.7.4.6, 13.7.5.8, 13.11.6, 13.12.8, 13.13.13, 13.15.6, 14.1.16, 14.2.13, 15.1.6.
export
VariableStatement, return VarScopedDeclarations of
VariableStatement.A Module Record encapsulates structural information about the imports and exports of a single module. This information is used to link the imports and exports of sets of connected modules. A Module Record includes four fields that are only used when evaluating a module.
For specification purposes Module Record values are values of the Record specification type and can be thought of as existing in a simple object-oriented hierarchy where Module Record is an abstract class with concrete subclasses. This specification only defines a single Module Record concrete subclass named Source Text Module Record. Other specifications and implementations may define additional Module Record subclasses corresponding to alternative module definition facilities that they defined.
Module Record defines the fields listed in Table 36. All Module Definition subclasses include at least those fields. Module Record also defines the abstract method list in Table 37. All Module definition subclasses must provide concrete implementations of these abstract methods.
Field Name | Value Type | Meaning |
---|---|---|
[[Realm]] | Realm Record | undefined | The Realm within which this module was created. undefined if not yet assigned. |
[[Environment]] | Lexical Environment | undefined | The Lexical Environment containing the top level bindings for this module. This field is set when the module is instantiated. |
[[Namespace]] | Object | undefined | The Module Namespace Object (26.3) if one has been created for this module. Otherwise undefined. |
[[Evaluated]] | Boolean | Initially false, true if evaluation of this module has started. Remains true when evaluation completes, even if it is an abrupt completion. |
Method | Purpose |
---|---|
GetExportedNames(exportStarSet) | Return a list of all names that are either directly or indirectly exported from this module. |
ResolveExport(exportName, resolveSet, exportStarSet) | Return the binding of a name exported by this modules. Bindings are represented by a Record of the form {[[module]]: Module Record, [[bindingName]]: String} |
ModuleDeclarationInstantiation() | Transitively resolve all module dependencies and create a module Environment Record for the module. |
ModuleEvaluation() |
Do nothing if this module has already been evaluated. Otherwise, transitively evaluate all module dependences of this module and then evaluate this module. ModuleDeclarationInstantiation must be completed prior to invoking this method. |
A Source Text Module Record is used to represent information about a module that was defined from ECMAScript source text (10) that was parsed using the goal symbol Module. Its fields contain digested information about the names that are imported by the module and its concrete methods use this digest to link, instantiate, and evaluate the module.
In addition to the fields, defined in Table 36, Source Text Module Records have the additional fields listed in Table 38. Each of these fields initially has the value undefined.
Field Name | Value Type | Meaning |
---|---|---|
[[ECMAScriptCode]] | a parse result | The result of parsing the source text of this module using Module as the goal symbol. |
[[RequestedModules]] | List of String | A List of all the ModuleSpecifier strings used by the module represented by this record to request the importation of a module. The List is source code occurrence ordered. |
[[ImportEntries]] | List of ImportEntry Records | A List of ImportEntry records derived from the code of this module. |
[[LocalExportEntries]] | List of ExportEntry Records | A List of ExportEntry records derived from the code of this module that correspond to declarations that occur within the module. |
[[IndirectExportEntries]] | List of ExportEntry Records | A List of ExportEntry records derived from the code of this module that correspond to reexported imports that occur within the module. |
[[StarExportEntries]] | List of ExportEntry Records | A List of ExportEntry records derived from the code of this module that correspond to export * declarations that occur within the module. |
An ImportEntry Record is a Record that digests information about a single declarative import. Each ImportEntry Record has the fields defined in Table 39:
Field Name | Value Type | Meaning |
---|---|---|
[[ModuleRequest]] | String | String value of the ModuleSpecifier of the ImportDeclaration. |
[[ImportName]] | String | The name under which the desired binding is exported by the module identified by [[ModuleRequest]]. The value "*" indicates that the import request is for the target module’s namespace object. |
[[LocalName]] | String | The name that is used to locally access the imported value from within the importing module. |
NOTE 1 Table 40 gives examples of ImportEntry records fields used to represent the syntactic import forms:
Import Statement Form |
[[ModuleRequest]] |
[[ImportName]] |
[[LocalName]] |
---|---|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
An ImportEntry Record is not created. |
An ExportEntry Record is a Record that digests information about a single declarative export. Each ExportEntry Record has the fields defined in Table 41:
Field Name | Value Type | Meaning |
---|---|---|
[[ExportName]] | String | The name used to export this binding by this module. |
[[ModuleRequest]] | String | null | The String value of the ModuleSpecifier of the ExportDeclaration. null if the ExportDeclaration does not have a ModuleSpecifier. |
[[ImportName]] | String | null | The name under which the desired binding is exported by the module identified by [[ModuleRequest]]. null if the ExportDeclaration does not have a ModuleSpecifier. "*" indicates that the export request is for all exported bindings. |
[[LocalName]] | String | null | The name that is used to locally access the exported value from within the importing module. null if the exported value is not locally accessible from within the module. |
NOTE 2 Table 42 gives examples of the ExportEntry record fields used to represent the syntactic export forms:
Export Statement Form |
[[ExportName]] |
[[ModuleRequest]] |
[[ImportName]] |
[[LocalName]] |
---|---|---|---|---|
|
|
null |
null |
|
|
|
null |
null |
|
|
|
null |
null |
|
|
|
null |
null |
|
|
|
null |
null |
|
|
|
null |
null |
|
|
|
|
|
null |
|
|
|
|
null |
|
null |
|
|
null |
The following definitions specify the required concrete methods and other abstract operations for Source Text Module Records
The abstract operation ParseModule with argument sourceText creates a Source Text Module Record based upon the result of parsing sourceText as a Module. ParseModule performs the following steps:
"*"
, then
"*"
, then
NOTE An implementation may parse module source text and analyze it for Early Error conditions prior to the evaluation of ParseModule for that module source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseModule upon that source text.
The GetExportedNames concrete method of a Source Text Module Record with argument exportStarSet performs the following steps:
"default"
) is false, then
NOTE GetExportedNames does not filter out or throw an exception for names that have ambiguous star export bindings.
The ResolveExport concrete method of a Source Text Module Record with arguments exportName, resolveSet, and exportStarSet performs the following steps:
"default"
) is true, then
default
export was not explicitly defined by
this module.default
export cannot be provided by an export *
."ambiguous"
, return "ambiguous"
."ambiguous"
.NOTE ResolveExport attempts to resolve an imported binding to the actual defining module and local binding name. The defining module may be the module represented by the Module Record this method was invoked on or some other module that is imported by that module. The parameter resolveSet is use to detect unresolved circular import/export paths. If a pair consisting of specific Module Record and exportName is reached that is already in resolveSet, an import circularity has been encountered. Before recursively calling ResolveExport, a pair consisting of module and exportName is added to resolveSet.
If a defining module is found a Record {[[module]], [[bindingName]]} is returned. This record identifies the
resolved binding of the originally requested export. If no definition was found or the request is found to be
circular, null is returned. If the request is found to be ambiguous, the string
"ambiguous"
is returned.
The ModuleDeclarationInstantiation concrete method of a Source Text Module Record performs the following steps:
"ambiguous"
, throw a
SyntaxError exception."*"
, then
"ambiguous"
, throw a
SyntaxError exception.The ModuleEvaluation concrete method of a Source Text Module Record performs the following steps:
HostResolveImportedModule is an implementation defined abstract operation that provides the concrete Module Record subclass instance that corresponds to the ModuleSpecifier String, specifier, occurring within the context of the module represented by the Module Record referencingModule.
The implementation of HostResolveImportedModule must conform to the following requirements:
The normal return value must be an instance of a concrete subclass of Module Record.
If a Module Record corresponding to the pair referencingModule, specifier does not exist or cannot be created, an exception must be thrown.
This operation must be idempotent if it completes normally. Each time it is called with a specific referencingModule, specifier pair as arguments it must return the same Module Record instance.
Multiple different referencingModule, specifier pairs may map to the same Module Record instance. The actual mapping semantic is implementation defined but typically a normalization process is applied to specifier as part of the mapping process. A typical normalization process would include actions such as alphabetic case folding and expansion of relative and abbreviated path specifiers.
The abstract operation GetModuleNamespace called with argument module performs the following steps:
"ambiguous"
, append name to unambiguousNames.A TopLevelModuleEvaluationJob with parameter sourceText is a job that parses, validates, and evaluates sourceText as a Module.
NOTE An implementation may parse a sourceText as a Module, analyze it for Early Error conditions, and instantiate it prior to the execution of the TopLevelModuleEvaluationJob for that sourceText. An implementation may also resolve, pre-parse and pre-analyze, and pre-instantiate module dependencies of sourceText. However, the reporting of any errors detected by these actions must be deferred until the TopLevelModuleEvaluationJob is actually executed.
NOTE The value of a ModuleItemList is the value of the last value producing item in the ModuleItemList.
import
ImportClause FromClause ;
import
ModuleSpecifier ;
,
NameSpaceImport,
NamedImports*
as
ImportedBinding{
}
{
ImportsList }
{
ImportsList ,
}
from
ModuleSpecifier,
ImportSpecifieras
ImportedBindingIt is a Syntax Error if the BoundNames of ImportDeclaration contains any duplicate entries.
See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.3.2.
import
ImportClause FromClause ;
import
ModuleSpecifier ;
,
NameSpaceImport,
NamedImports{
}
,
ImportSpecifieras
ImportedBindingSee also: 15.2.1.8.
import
ImportClause FromClause ;
import
ModuleSpecifier ;
With parameter module.
,
NameSpaceImport,
NamedImportsImportedDefaultBinding : ImportedBinding
"default"
,
[[LocalName]]: localName }.*
as
ImportedBinding"*"
, [[LocalName]]:
localName }.{
}
,
ImportSpecifieras
ImportedBindingimport
ImportClause FromClause ;
export
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclaration[Default]export
default
ClassDeclaration[Default]export
default
[lookahead ∉ {function
, class
}] AssignmentExpression[In] ;
{
}
{
ExportsList }
{
ExportsList ,
}
,
ExportSpecifieras
IdentifierNameexport
ExportClause ;
For each IdentifierName n in ReferencedBindings of ExportClause : It is
a
Syntax Error if
StringValue of
n is a ReservedWord
or if the StringValue of n is one of: "implements"
, "interface"
,
"let"
, "package"
, "private"
, "protected"
, "public"
,
"static"
, or "yield"
.
NOTE The above rule means that each ReferencedBindings of ExportClause is treated as an IdentifierReference.
See also: 12.1.2, 13.3.1.2, 13.3.2.1, 13.3.3.1, 13.7.5.2, 14.1.3, 14.2.2, 14.4.2, 14.5.2, 15.2.2.2.
export
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclaration"*default*"
, append "*default*"
to
declarationNames.export
default
ClassDeclaration"*default*"
, append "*default*"
to
declarationNames.ExportDeclaration : export default
AssignmentExpression
;
"*default*"
».See also: 15.2.1.5.
export
ExportClause FromClause ;
export
*
FromClause ;
export
ExportClause ;
export
VariableStatementexport
DeclarationExportDeclaration : export
default
HoistableDeclaration
ExportDeclaration : export
default
ClassDeclaration
ExportDeclaration : export
default
AssignmentExpression ;
{
}
,
ExportSpecifieras
IdentifierNameSee also: 15.2.1.6.
export
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
DeclarationExportDeclaration : export
default
HoistableDeclaration
ExportDeclaration : export
default
ClassDeclaration
ExportDeclaration : export
default
AssignmentExpression ;
"default"
».{
}
,
ExportSpecifieras
IdentifierNameSee also: 15.2.1.7.
export
*
FromClause ;
"*"
, [[LocalName]]:
null, [[ExportName]]: null }.export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclaration"default"
}.export
default
ClassDeclaration"default"
}.ExportDeclaration : export default
AssignmentExpression;
"*default*"
, [[ExportName]]: "default"
}.NOTE "*default*"
is used within this specification as a synthetic name for
anonymous default export values.
With parameter module.
{
}
,
ExportSpecifieras
IdentifierNameSee also: 13.3.1.3, 14.1.10, 14.4.8, 14.5.7.
export
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
default
AssignmentExpression ;
NOTE It is not necessary to treat export
default
AssignmentExpression as a constant declaration because there is no syntax that permits assignment to
the internal bound name used to reference a module’s default object.
See also: 13.2.6, 13.12.6, 13.13.7, 14.1.14, 14.2.11, 15.1.4, 15.2.1.12.
export
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclarationexport
default
ClassDeclarationExportDeclaration : export default
AssignmentExpression
;
See also: 15.2.1.10, 15.2.2.5.
ExportDeclaration : export
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclarationexport
default
ClassDeclarationexport
default
AssignmentExpression ;
{
}
,
ExportSpecifieras
IdentifierNameexport
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclarationexport
default
ClassDeclaration"*default*"
, then
"name"
)."default"
)."*default*"
,
value, env).ExportDeclaration : export default
AssignmentExpression
;
"name"
)."default"
)."*default*"
,
value, env).An implementation must report most errors at the time the relevant ECMAScript language construct is evaluated. An early
error is an error that can be detected and reported prior to the evaluation of any construct in the Script containing the error. The presence of an early error prevents the evaluation of the construct. An
implementation must report early errors in a Script as part of the ScriptEvaluationJob for that Script. Early errors in a Module are reported at the point when the Module would be evaluated and the Module is never initialized. Early errors in eval code are reported at the time eval
is
called and prevent evaluation of the eval code. All errors that are not early errors are runtime errors.
An implementation must report as an early error any occurrence of a condition that is listed in a “Static Semantics: Early Errors” subclause of this specification.
An implementation shall not treat other kinds of errors as early errors even if the compiler can prove that a construct cannot execute without error under any circumstances. An implementation may issue an early warning in such a case, but it should not report the error until the relevant construct is actually executed.
An implementation shall report all errors as specified, except for the following:
Except as restricted in 16.1, an implementation may extend Script
syntax, Module syntax, and regular expression pattern or flag syntax. To permit this, all operations (such as
calling eval
, using a regular expression literal, or using the Function
or RegExp
constructor) that are allowed to throw SyntaxError are permitted to exhibit implementation-defined behaviour
instead of throwing SyntaxError when they encounter an implementation-defined extension to the script syntax or
regular expression pattern or flag syntax.
Except as restricted in 16.1, an implementation may provide additional types, values, objects, properties, and functions beyond those described in this specification. This may cause constructs (such as looking up a variable in the global scope) to have implementation-defined behaviour instead of throwing an error (such as ReferenceError).
An implementation may define behaviour other than throwing RangeError for toFixed
,
toExponential
, and toPrecision
when the fractionDigits or precision argument
is outside the specified range.
An implementation must not extend this specification in the following ways:
Other than as defined in this specification, ECMAScript Function objects defined using syntactic constructors in strict mode code must not be created with own properties named "caller"
or
"arguments"
other than those that are created by applying the AddRestrictedFunctionProperties abstract operation (9.2.7) to the function. Such own properties also must not be created for
function objects defined using an ArrowFunction, MethodDefinition, GeneratorDeclaration, GeneratorExpression, ClassDeclaration, or ClassExpression regardless of whether the definition
is contained in strict mode code. Built-in functions, strict mode functions
created using the Function
constructor, generator functions created using the Generator
constructor, and functions created using the bind
method also must not be created with such own
properties.
If an implementation extends non-strict or built-in function objects with an own property named "caller"
the value of that property, as observed using [[Get]] or [[GetOwnProperty]], must not be a strict function object. If it
is an accessor property, the function that is the value of the property’s [[Get]] attribute must never return a
strict function when called.
The behaviour of the following methods must not be extended except as specified in ECMA-402: Object.prototype.toLocaleString
, Array.prototype.toLocaleString
, Number.prototype.toLocaleString
, Date.prototype.toLocaleDateString
, Date.prototype.toLocaleString
, Date.prototype.toLocaleTimeString
, String.prototype.localeCompare
.
The RegExp pattern grammars in 21.2.1 and B.1.4 must not be extended to recognize any of the source characters A-Z or a-z as IdentityEscape[U] when the U grammar parameter is present.
The Syntactic Grammar must not be extended in any manner that allows the token :
to immediate follow
source text that matches the BindingIdentifier nonterminal symbol.
When processing strict mode code, the syntax of NumericLiteral must not be extended to include LegacyOctalIntegerLiteral as defined in B.1.1.
TemplateCharacter (11.8.6) must not be extended to include LegacyOctalEscapeSequence as defined in B.1.2.
When processing strict mode code, the extensions defined in B.3.1, B.3.2, B.3.3, and B.3.4 must not be supported.
When parsing for the Module goal symbol, the lexical grammar extensions defined in B.1.3 must not be supported.
There are certain built-in objects available whenever an ECMAScript Script or Module begins execution. One, the global object, is part of the lexical environment of the executing program. Others are accessible as initial properties of the global object or indirectly as properties of accessible built-in objects.
Unless specified otherwise, a built-in object that is callable as a function is a built-in Function object with the characteristics described in 9.3. Unless specified otherwise, the [[Extensible]] internal slot of a built-in object initially has the value true. Every built-in Function object has a [[Realm]] internal slot whose value is the code Realm for which the object was initially created.
Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore are constructors: they are
functions intended for use with the new
operator. For each built-in function, this specification describes the
arguments required by that function and the properties of that function object. For each built-in constructor, this
specification furthermore describes properties of the prototype object of that constructor and properties of specific object
instances returned by a new
expression that invokes that constructor.
Unless otherwise specified in the description of a particular function, if a built-in function or constructor is given fewer
arguments than the function is specified to require, the function or constructor shall behave exactly as if it had been given
sufficient additional arguments, each such argument being the undefined value. Such missing arguments are considered to
be “not present” and may be identified in that manner by specification algorithms. In the description of a
particular function, the terms “this
value” and
“NewTarget” have the meanings given in 9.3.
Unless otherwise specified in the description of a particular function, if a built-in function or constructor described is given more arguments than the function is specified to allow, the extra arguments are evaluated by the call and then ignored by the function. However, an implementation may define implementation specific behaviour relating to such arguments as long as the behaviour is not the throwing of a TypeError exception that is predicated simply on the presence of an extra argument.
NOTE 1 Implementations that add additional capabilities to the set of built-in functions are encouraged to do so by adding new functions rather than adding new parameters to existing functions.
Unless otherwise specified every built-in function and every built-in constructor has the Function prototype object, which is
the initial value of the expression Function.prototype
(19.2.3), as the value of its [[Prototype]] internal slot.
Unless otherwise specified every built-in prototype object has the Object prototype object, which is the initial value of the
expression Object.prototype
(19.1.3), as the value of
its [[Prototype]] internal slot, except the Object prototype
object itself.
Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method unless otherwise specified in the description of a particular function.
Unless otherwise specified, each built-in function defined in this specification is created as if by calling the CreateBuiltinFunction abstract operation (9.3.3).
Every built-in Function object, including constructors, has a length
property whose value is an integer. Unless
otherwise specified, this value is equal to the largest number of named arguments shown in the subclause headings for the
function description, including optional parameters. However, rest parameters shown using the form “...name” are not
included in the default argument count.
NOTE 2 For example, the function object that is the initial value of the slice
property of the String prototype object is described under the subclause heading “String.prototype.slice (start, end)” which shows the two named arguments start
and end; therefore the value of the length
property of that Function object is 2
.
Unless otherwise specified, the length
property of a built-in Function object has the attributes
{ [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Every built-in Function object, including constructors, that is not identified as an anonymous function has a
name
property whose value is a String. Unless otherwise specified, this value is the name that is given to the
function in this specification. For functions that are specified as properties of objects, the name value is the property name
string used to access the function. Functions that are specified as get or set accessor functions of built-in properties have
"get "
or "set "
prepended to the property name string. The value of the name
property is
explicitly specified for each built-in functions whose property key is a Symbol value.
Unless otherwise specified, the name
property of a built-in Function object, if it exists, has the attributes
{ [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Every other data property described in clauses 18 through 26 and in Annex B.2 has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true } unless otherwise specified.
Every accessor property described in clauses 18 through 26 and in Annex B.2 has the attributes {[[Enumerable]]: false, [[Configurable]]: true } unless otherwise specified. If only a get accessor function is described, the set accessor function is the default value, undefined. If only a set accessor is described the get accessor is the default value, undefined.
The unique global object is created before control enters any execution context.
The global object does not have a [[Construct]] internal method; it is not possible to use the global object as a
constructor with the new
operator.
The global object does not have a [[Call]] internal method; it is not possible to invoke the global object as a function.
The value of the [[Prototype]] internal slot of the global object is implementation-dependent.
In addition to the properties defined in this specification the global object may have additional host defined properties.
This may include a property whose value is the global object itself; for example, in the HTML document object model the
window
property of the global object is the global object itself.
The value of Infinity
is +∞ (see
6.1.6). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
false }.
The value of NaN
is NaN (see 6.1.6). This
property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false
}.
The value of undefined
is undefined (see
6.1.1). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
false }.
The eval
function is the %eval% intrinsic object. When the eval
function
is called with one argument x, the following steps are taken:
The abstract operation PerformEval with arguments x, evalRealm, strictCaller, and direct performs the following steps:
eval
. If direct is false ctx will be the execution context for the invocation of the eval function.NOTE The eval code cannot instantiate variable or function bindings in the variable
environment of the calling context that invoked the eval if the calling context is evaluating formal parameter
initializers or if either the code of the calling context or the eval code is strict
code. Instead such bindings are instantiated in a new VariableEnvironment that
is only accessible to the eval code. Bindings introduced by let
, const
, or class
declarations are always instantiated in a new LexicalEnvironment.
When the abstract operation EvalDeclarationInstantiation is called with arguments body, varEnv, lexEnv, and strict the following steps are taken:
eval
will not create a global var declaration that would be shadowed by a global
lexical declaration.eval
will not hoist var declaration over a like-named lexical
declaration.NOTE An alternative version of this algorithm is described in B.3.5.
The isFinite
function is the %isFinite% intrinsic object. When the
isFinite
function is called with one argument x, the following steps are taken:
The isNaN
function is the %isNaN% intrinsic object. When the isNaN
function is called with one argument number, the following steps are taken:
NOTE A reliable way for ECMAScript code to test if a value X
is a NaN is an
expression of the form X !== X
. The result will be true if and only if X
is a
NaN.
The parseFloat
function produces a Number value dictated by interpretation of the contents of the
string argument as a decimal literal.
The parseFloat
function is the %parseFloat% intrinsic object. When the
parseFloat
function is called with one argument string, the following steps are taken:
"-"
, return −0.NOTE parseFloat
may interpret only a leading portion of string as a
Number value; it ignores any code units that cannot be interpreted as part of the notation of an decimal literal, and no
indication is given that any such code units were ignored.
The parseInt
function produces an integer value dictated by interpretation of the contents of the
string argument according to the specified radix. Leading white space in string is ignored.
If radix is undefined or 0, it is assumed to be 10
except when the number begins with the code unit pairs 0x
or 0X
, in which case a radix of 16 is
assumed. If radix is 16, the number may also optionally begin
with the code unit pairs 0x
or 0X
.
The parseInt
function is the %parseInt% intrinsic object. When the
parseInt
function is called, the following steps are taken:
"0x"
or
"0X"
, remove the first two code units from S and let R = 16.NOTE parseInt
may interpret only a leading portion of string as an
integer value; it ignores any code units that cannot be interpreted as part of the notation of an integer, and no
indication is given that any such code units were ignored.
Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or files) and transport protocols by which to access them (e.g. HTTP or FTP) on the Internet. The ECMAScript language itself does not provide any support for using URIs except for functions that encode and decode URIs as described in 18.2.6.2, 18.2.6.3, 18.2.6.4 and 18.2.6.5
NOTE Many implementations of ECMAScript provide additional functions and methods that manipulate web pages; these functions are beyond the scope of this standard.
A URI is composed of a sequence of components separated by component separators. The general form is:
Scheme : First /
Second ;
Third ?
Fourth
where the italicized names represent components and “:
”, “/
”,
“;
” and “?
” are reserved for use as separators. The
encodeURI
and decodeURI
functions are intended to work with complete URIs; they assume that
any reserved code units in the URI are intended to have special meaning and so are not encoded. The
encodeURIComponent
and decodeURIComponent
functions are intended to work with the individual
component parts of a URI; they assume that any reserved code units represent text and so must be encoded so that they
are not interpreted as reserved code units when the component is part of a complete URI.
The following lexical grammar specifies the form of encoded URIs.
;
/
?
:
@
&
=
+
$
,
%
HexDigit HexDigita
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
-
_
.
!
~
*
'
(
)
NOTE The above syntax is based upon RFC 2396 and does not reflect changes introduced by the more recent RFC 3986.
Runtime Semantics
When a code unit to be included in a URI is not listed above or is not intended to have the special meaning sometimes
given to the reserved code units, that code unit must be encoded. The code unit is transformed into its UTF-8 encoding,
with surrogate pairs first converted from UTF-16 to the corresponding code point value. (Note that for code units in the
range [0,127] this results in a single octet with the same value.) The resulting sequence of octets is then transformed
into a String with each octet represented by an escape sequence of the form "%xx"
.
The encoding and escaping process is described by the abstract operation Encode taking two String arguments string and unescapedSet.
"%
XY"
where
XY are two uppercase hexadecimal digits encoding the value of jOctet.The unescaping and decoding process is described by the abstract operation Decode taking two String arguments string and reservedSet.
"%"
, then
"%"
,
"%"
, throw a URIError exception.NOTE This syntax of Uniform Resource Identifiers is based upon RFC 2396 and does not reflect the more recent RFC 3986 which replaces RFC 2396. A formal description and implementation of UTF-8 is given in RFC 3629.
In UTF-8, characters are encoded using sequences of 1 to 6 octets. The only octet of a sequence of one has the higher-order bit set to 0, the remaining 7 bits being used to encode the character value. In a sequence of n octets, n>1, the initial octet has the n higher-order bits set to 1, followed by a bit set to 0. The remaining bits of that octet contain bits from the value of the character to be encoded. The following octets all have the higher-order bit set to 1 and the following bit set to 0, leaving 6 bits in each to contain bits from the character to be encoded. The possible UTF-8 encodings of ECMAScript characters are specified in Table 43.
Code Unit Value | Representation | 1st Octet | 2nd Octet | 3rd Octet | 4th Octet |
---|---|---|---|---|---|
0x0000 - 0x007F |
00000000 0zzzzzzz |
0zzzzzzz |
|||
0x0080 - 0x07FF |
00000yyy yyzzzzzz |
110yyyyy |
10zzzzzz |
||
0x0800 - 0xD7FF |
xxxxyyyy yyzzzzzz | 1110xxxx |
10yyyyyy |
10zzzzzz |
|
0xD800 - 0xDBFF followed by0xDC00 – 0xDFFF |
110110vv vvwwwwxx followed by110111yy yyzzzzzz |
11110uuu |
10uuwwww |
10xxyyyy |
10zzzzzz |
0xD800 - 0xDBFF not followed by0xDC00 – 0xDFFF |
causes URIError |
||||
0xDC00 – 0xDFFF |
causes URIError |
||||
0xE000 - 0xFFFF |
xxxxyyyy yyzzzzzz | 1110xxxx |
10yyyyyy |
10zzzzzz |
Where
uuuuu =
vvvv + 1
to account for the addition of 0x10000 as in Surrogates, section 3.7, of the Unicode Standard.
The range of code unit values 0xD800-0xDFFF is used to encode surrogate pairs; the above transformation combines a UTF-16 surrogate pair into a UTF-32 representation and encodes the resulting 21-bit value in UTF-8. Decoding reconstructs the surrogate pair.
RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the invalid sequence C0 80 must not decode into the code unit 0x0000. Implementations of the Decode algorithm are required to throw a URIError when encountering such invalid sequences.
The decodeURI
function computes a new version of a URI in which each escape sequence and UTF-8 encoding of
the sort that might be introduced by the encodeURI
function is replaced with the UTF-16 encoding of the code
points that it represents. Escape sequences that could not have been introduced by encodeURI
are not
replaced.
The decodeURI
function is the %decodeURI% intrinsic object. When the
decodeURI
function is called with one argument encodedURI, the following steps are taken:
"#"
.NOTE The code point "#"
is not decoded from escape sequences even though it is
not a reserved URI code point.
The decodeURIComponent
function computes a new version of a URI in which each escape sequence and UTF-8
encoding of the sort that might be introduced by the encodeURIComponent
function is replaced with the UTF-16
encoding of the code points that it represents.
The decodeURIComponent
function is the %decodeURIComponent% intrinsic object. When
the decodeURIComponent
function is called with one argument encodedURIComponent, the following
steps are taken:
The encodeURI
function computes a new version of a UTF-16 encoded (6.1.4) URI in which each instance of certain code points is replaced
by one, two, three, or four escape sequences representing the UTF-8 encoding of the code points.
The encodeURI
function is the %encodeURI% intrinsic object. When the
encodeURI
function is called with one argument uri, the following steps are
taken:
#
".NOTE The code unit "#"
is not encoded to an escape sequence even though it is
not a reserved or unescaped URI code point.
The encodeURIComponent
function computes a new version of a UTF-16 encoded (6.1.4) URI in which each instance of certain code points is replaced
by one, two, three, or four escape sequences representing the UTF-8 encoding of the code point.
The encodeURIComponent
function is the %encodeURIComponent% intrinsic object. When
the encodeURIComponent
function is called with one argument uriComponent, the
following steps are taken:
See 22.1.1.
See 24.1.2.
See 19.3.1.
See 24.2.2.
See 20.3.2.
See 19.5.1.
See 19.5.5.1.
See 22.2.4.
See 22.2.4.
See 19.2.1.
See 22.2.4.
See 22.2.4.
See 22.2.4.
See 23.1.1.
See 20.1.1.
See 19.1.1.
See 26.2.1.
See 25.4.3.
See 19.5.5.2.
See 19.5.5.3.
See 21.2.3.
See 23.2.1.
See 21.1.1.
See 19.4.1.
See 19.5.5.4.
See 19.5.5.5.
See 22.2.4.
See 22.2.4.
See 22.2.4.
See 22.2.4.
See 19.5.5.6.
See 23.3.1.
See 23.4.
See 24.3.
See 20.2.
See 26.1.
The Object constructor is the %Object% intrinsic object and the initial value of the Object
property of
the global object. When called as a constructor it creates a new ordinary object. When Object
is called as a
function rather than as a constructor, it performs a type conversion.
The Object
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition.
When Object
function is called with optional argument value, the following
steps are taken:
"%ObjectPrototype%"
).The value of the [[Prototype]] internal slot of the Object constructor is the intrinsic object %FunctionPrototype%.
Besides the length
property (whose value is 1), the Object constructor has the following
properties:
The assign function is used to copy the values of all of the enumerable own properties from one or more source objects to a target object. When the assign function is called, the following steps are taken:
The length
property of the assign
method is 2.
The create function creates a new object with a specified prototype. When the create function is called, the following steps are taken:
The defineProperties function is used to add own properties and/or update the attributes of existing own properties of an object. When the defineProperties function is called, the following steps are taken:
The abstract operation ObjectDefineProperties with arguments O and Properties performs the following steps:
The defineProperty function is used to add an own property and/or update the attributes of an existing own property of an object. When the defineProperty function is called, the following steps are taken:
When the freeze function is called, the following steps are taken:
frozen
").When the getOwnPropertyDescriptor
function is called, the following steps are
taken:
When the getOwnPropertyNames function is called, the following steps are taken:
When the getOwnPropertySymbols function is called with argument O, the following steps are taken:
The abstract operation GetOwnPropertyKeys is called with arguments O and Type where O is an Object and Type is one of the ECMAScript specification types String or Symbol. The following steps are taken:
When the getPrototypeOf
function is called with argument O, the following
steps are taken:
When the is function is called with arguments value1 and value2 the following steps are taken:
When the isExtensible function is called with argument O, the following steps are taken:
When the isFrozen function is called with argument O, the following steps are taken:
frozen
").When the isSealed function is called with argument O, the following steps are taken:
sealed
").When the keys function is called with argument O, the following steps are taken:
If an implementation defines a specific order of enumeration for the for-in statement, the same order must be used for the elements of the array returned in step 4.
When the preventExtensions function is called, the following steps are taken:
The initial value of Object.prototype
is the intrinsic object %ObjectPrototype% (19.1.3).
This property has the attributes {[[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
When the seal function is called, the following steps are taken:
sealed
").When the setPrototypeOf
function is called with arguments O and proto, the following steps are taken:
The Object prototype object is the intrinsic object %ObjectPrototype%. The Object prototype object is an ordinary object.
The value of the [[Prototype]] internal slot of the Object prototype object is null and the initial value of the [[Extensible]] internal slot is true.
The initial value of Object.prototype.constructor
is the intrinsic object %Object%.
When the hasOwnProperty
method is called with argument V, the following
steps are taken:
NOTE The ordering of steps 1 and 3 is chosen to ensure that any exception that would have been thrown by step 1 in previous editions of this specification will continue to be thrown even if the this value is undefined or null.
When the isPrototypeOf
method is called with argument V, the following
steps are taken:
NOTE The ordering of steps 1 and 2 preserves the behaviour specified by previous editions of this specification for the case where V is not an object and the this value is undefined or null.
When the propertyIsEnumerable
method is called with argument V, the
following steps are taken:
NOTE 1 This method does not consider objects in the prototype chain.
NOTE 2 The ordering of steps 1 and 3 is chosen to ensure that any exception that would have been thrown by step 1 in previous editions of this specification will continue to be thrown even if the this value is undefined or null.
When the toLocaleString method is called, the following steps are taken:
"toString"
).The optional parameters to this function are not used but are intended to correspond to the parameter pattern used by
ECMA-402 toLocalString
functions. Implementations that do not include ECMA-402 support must not use those
parameter positions for other purposes.
The length
property of the toLocaleString
method is 0.
NOTE 1 This function provides a generic toLocaleString
implementation for
objects that have no locale-specific toString
behaviour. Array
, Number
,
Date
, and Typed Arrays
provide their own locale-sensitive toLocaleString
methods.
NOTE 2 ECMA-402 intentionally does not provide an alternative to this default implementation.
When the toString
method is called, the following steps are taken:
"[object Undefined]"
."[object Null]"
."Array"
."String"
."Arguments"
."Function"
."Error"
."Boolean"
."Number"
."Date"
."RegExp"
."Object"
."[object "
, tag, and
"]"
.This function is the %ObjProto_toString% intrinsic object.
NOTE Historically, this function was occasionally used to access the String value of the
[[Class]] internal slot that was used in previous editions
of this specification as a nominal type tag for various built-in objects. The above definition of toString
preserves compatibility for legacy code that uses toString
as a test for those specific kinds of built-in
objects. It does not provide a reliable type testing mechanism for other kinds of built-in or program defined objects.
In addition, programs can use @@toStringTag in ways that will invalidate the reliability of such legacy type tests.
When the valueOf method is called, the following steps are taken:
Object instances have no special properties beyond those inherited from the Object prototype object.
The Function constructor is the %Function% intrinsic object and the initial value of the Function
property
of the global object. When Function
is called as a function rather than as a constructor, it creates and
initializes a new Function object. Thus the function call Function(…)
is equivalent to
the object creation expression new Function(…)
with the same arguments.
The Function
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
Function
behaviour must include a super
call to the Function
constructor to create
and initialize a subclass instances with the internal slots necessary for built-in function behaviour. All ECMAScript
syntactic forms for defining function objects create instances of Function
. There is no syntactic means to
create instances of Function
subclasses except for the built-in Generator Function subclass.
The last argument specifies the body (executable code) of a function; any preceding arguments specify formal parameters.
When the Function
function is called with some arguments p1,
p2, … , pn, body (where n might be 0, that is, there are no “p” arguments, and where body might also
not be provided), the following steps are taken:
"normal"
,
args).NOTE It is permissible but not necessary to have one argument for each formal parameter to be specified. For example, all three of the following expressions produce the same result:
new Function("a", "b", "c", "return a+b+c")
new Function("a, b, c", "return a+b+c")
new Function("a,b", "c", "return a+b+c")
The abstract operation CreateDynamicFunction is called with arguments constructor, newTarget,
kind, and args. constructor is the constructor function that is performing this action,
newTarget is the constructor that new
was initially applied to, kind is either
"normal"
or "generator"
, and args is a List containing the actual argument values that were passed to
constructor. The following steps are taken:
"normal"
, then
"%FunctionPrototype%"
."%Generator%"
.","
(a
comma), and nextArgString."generator"
, then
"generator"
, then
"anonymous"
).NOTE A prototype
property is automatically created for every function created
using CreateDynamicFunction , to provide for the possibility that the function will be used as a constructor.
The Function
constructor is itself a built-in function object. The value of the [[Prototype]] internal slot of the Function
constructor is
%FunctionPrototype%, the intrinsic Function prototype object (19.2.3).
The value of the [[Extensible]] internal slot of the Function constructor is true.
The Function constructor has the following properties:
This is a data property with a value of 1. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The value of Function.prototype
is %FunctionPrototype%, the intrinsic Function prototype object (19.2.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Function prototype object is the intrinsic object %FunctionPrototype%. The Function prototype object is itself a built-in function object. When invoked, it accepts any arguments and returns undefined. It does not have a [[Construct]] internal method so it is not a constructor.
NOTE The Function prototype object is specified to be a function object to ensure compatibility with ECMAScript code that was created prior to the ECMAScript 2015 specification.
The value of the [[Prototype]] internal slot of the Function prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The initial value of the [[Extensible]] internal slot of the Function prototype object is true.
The Function prototype object does not have a prototype
property.
The value of the length
property of the Function prototype object is 0.
The value of the name
property of the Function prototype object is the empty String.
When the apply
method is called on an object func with arguments
thisArg and argArray, the following steps are taken:
The length
property of the apply
method is 2.
NOTE 1 The thisArg value is passed without modification as the this value. This is a change from Edition 3, where an undefined or null thisArg is replaced with the global object and ToObject is applied to all other values and that result is passed as the this value. Even though the thisArg is passed without modification, non-strict functions still perform these transformations upon entry to the function.
NOTE 2 If func is an arrow function or a bound function then the thisArg will be ignored by the function [[Call]] in step 6.
When the bind
method is called with argument thisArg and zero or more
args, it performs the following steps:
"length"
)."length"
)."length"
,
PropertyDescriptor {[[Value]]: L, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
true})."name"
)."bound"
).The length
property of the bind
method is 1.
NOTE 1 Function objects created using Function.prototype.bind
are exotic
objects. They also do not have a prototype
property.
NOTE 2 If Target is an arrow function or a bound function then the thisArg passed to this method will not be used by subsequent calls to F.
When the call
method is called on an object func with argument,
thisArg and zero or more args, the following steps are taken:
The length
property of the call
method is 1.
NOTE 1 The thisArg value is passed without modification as the this value. This is a change from Edition 3, where an undefined or null thisArg is replaced with the global object and ToObject is applied to all other values and that result is passed as the this value. Even though the thisArg is passed without modification, non-strict functions still perform these transformations upon entry to the function.
NOTE 2 If func is an arrow function or a bound function then the thisArg will be ignored by the function [[Call]] in step 5.
The initial value of Function.prototype.constructor
is the intrinsic object %Function%.
When the toString
method is called on an object func the following steps
are taken:
toString
Representation Requirements:
The string representation must have the syntax of a FunctionDeclaration, FunctionExpression, GeneratorDeclaration, GeneratorExpression, ClassDeclaration, ClassExpression, ArrowFunction, MethodDefinition, or GeneratorMethod depending upon the actual characteristics of the object.
The use and placement of white space, line terminators, and semicolons within the representation String is implementation-dependent.
If the object was defined using ECMAScript code and the returned string representation is not in the form of a
MethodDefinition or GeneratorMethod then the representation must be such that if the string is
evaluated, using eval
in a lexical context that is equivalent to the lexical context used to create the
original object, it will result in a new functionally equivalent object. In that case the returned source code must
not mention freely any variables that were not mentioned freely by the original function’s source code, even if
these “extra” names were originally in scope.
If the implementation cannot produce a source code string that meets these criteria then it must return a string
for which eval
will throw a SyntaxError
exception.
When the @@hasInstance method of an object F is called with value V, the following steps are taken:
The value of the name
property of this function is "[Symbol.hasInstance]"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE This is the default implementation of @@hasInstance
that most functions
inherit. @@hasInstance
is called by the instanceof
operator to determine whether a value is an
instance of a specific constructor. An expression such as
v instanceof F
evaluates as
F[@@hasInstance](v)
A constructor function can control which objects are recognized as its instances by instanceof
by
exposing a different @@hasInstance
method on the function.
This property is non-writable and non-configurable to prevent tampering that could be used to globally expose the target function of a bound function.
Every function instance is an ECMAScript function object and has the
internal slots listed in Table 27. Function instances created using the Function.prototype.bind
method (19.2.3.2) have the internal slots listed in Table 28.
The Function instances have the following properties:
The value of the length
property is an integer that indicates the typical number of arguments expected by
the function. However, the language permits the function to be invoked with some other number of arguments. The behaviour
of a function when invoked on a number of arguments other than the number specified by its length
property
depends on the function. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false,
[[Configurable]]: true }.
The value of the name
property is an String that is descriptive of the function. The name has no semantic
significance but is typically a variable or property name that is used to refer to the function at its point of definition
in ECMAScript code. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false,
[[Configurable]]: true }.
Anonymous functions objects that do not have a contextual name associated with them by this specification do not have a
name
own property but inherit the name
property of %FunctionPrototype%.
Function instances that can be used as a constructor have a prototype
property. Whenever such a function
instance is created another ordinary object is also created and is the initial value of the function’s
prototype
property. Unless otherwise specified, the value of the prototype
property is used to
initialize the [[Prototype]] internal slot of the object
created when that function is invoked as a constructor.
This property has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE Function objects created using Function.prototype.bind
, or by evaluating a MethodDefinition (that are not a GeneratorMethod) or an ArrowFunction grammar production do not have a prototype
property.
The Boolean constructor is the %Boolean% intrinsic object and the initial value of the Boolean
property of
the global object. When called as a constructor it creates and initializes a new Boolean object. When Boolean
is called as a function rather than as a constructor, it performs a type conversion.
The Boolean
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
Boolean
behaviour must include a super
call to the Boolean
constructor to create
and initialize the subclass instance with a [[BooleanData]] internal slot.
When Boolean
is called with argument value, the following steps are
taken:
"%BooleanPrototype%"
, «[[BooleanData]]» ).The value of the [[Prototype]] internal slot of the Boolean constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 1), the Boolean constructor has the following
properties:
The initial value of Boolean.prototype
is the intrinsic object %BooleanPrototype% (19.3.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Boolean prototype object is the intrinsic object %BooleanPrototype%. The Boolean prototype object is an ordinary object. It is not a Boolean instance and does not have a [[BooleanData]] internal slot.
The value of the [[Prototype]] internal slot of the Boolean prototype object is the intrinsic object %ObjectPrototype% (19.1.3).
The abstract operation thisBooleanValue(value) performs the following steps:
The initial value of Boolean.prototype.constructor
is the intrinsic object %Boolean%.
The following steps are taken:
"true"
; else return "false"
.The following steps are taken:
Boolean instances are ordinary objects that inherit properties from the Boolean prototype object. Boolean instances have a [[BooleanData]] internal slot. The [[BooleanData]] internal slot is the Boolean value represented by this Boolean object.
The Symbol constructor is the %Symbol% intrinsic object and the initial value of the Symbol
property of
the global object. When Symbol
is called as a function, it returns a new Symbol value.
The Symbol
constructor is not intended to be used with the new
operator or to be subclassed.
It may be used as the value of an extends
clause of a class definition but a super
call to the
Symbol
constructor will cause an exception.
When Symbol
is called with optional argument description, the following
steps are taken:
The value of the [[Prototype]] internal slot of the Symbol constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 0), the Symbol constructor has the
following properties:
When Symbol.for
is called with argument key it performs the following
steps:
The GlobalSymbolRegistry is a List that is globally available. It is shared by all Code Realms. Prior to the evaluation of any ECMAScript code it is initialized as an empty List. Elements of the GlobalSymbolRegistry are Records with the structure defined in Table 44.
Field Name | Value | Usage |
---|---|---|
[[key]] | A String | A string key used to globally identify a Symbol. |
[[symbol]] | A Symbol | A symbol that can be retrieved from any Realm. |
The initial value of Symbol.hasInstance
is the well known symbol @@hasInstance (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.isConcatSpreadable
is the well known symbol @@isConcatSpreadable (Table 1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.iterator
is the well known symbol @@iterator (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
When Symbol.keyFor
is called with argument sym it performs the following
steps:
The initial value of Symbol.match
is the well known symbol @@match (Table 1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.prototype
is the intrinsic object %SymbolPrototype% (19.4.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.replace
is the well known symbol @@replace (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.search
is the well known symbol @@search (Table 1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.species
is the well known symbol @@species (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.split
is the well known symbol @@split (Table 1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.toPrimitive
is the well known symbol @@toPrimitive (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.toStringTag
is the well known symbol @@toStringTag (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Symbol.unscopables
is the well known symbol @@unscopables (Table
1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Symbol prototype object is the intrinsic object %SymbolPrototype%. The Symbol prototype object is an ordinary object. It is not a Symbol instance and does not have a [[SymbolData]] internal slot.
The value of the [[Prototype]] internal slot of the Symbol prototype object is the intrinsic object %ObjectPrototype% (19.1.3).
The initial value of Symbol.prototype.constructor
is the intrinsic object %Symbol%.
The following steps are taken:
When the abstract operation SymbolDescriptiveString is called with argument sym, the following steps are taken:
The following steps are taken:
This function is called by ECMAScript language operators to convert a Symbol object to a primitive value. The allowed
values for hint are "default"
, "number"
, and "string"
.
When the @@toPrimitive
method is called with argument hint, the following
steps are taken:
The value of the name
property of this function is "[Symbol.toPrimitive]"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The initial value of the @@toStringTag property is the String value "Symbol"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Symbol instances are ordinary objects that inherit properties from the Symbol prototype object. Symbol instances have a [[SymbolData]] internal slot. The [[SymbolData]] internal slot is the Symbol value represented by this Symbol object.
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
The Error constructor is the %Error% intrinsic object and the initial value of the Error
property of the
global object. When Error
is called as a function rather than as a constructor, it creates and initializes a
new Error object. Thus the function call Error(…)
is equivalent to the object creation
expression new Error(…)
with the same arguments.
The Error
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
Error
behaviour must include a super
call to the Error
constructor to create and
initialize subclass instances with a [[ErrorData]] internal
slot.
When the Error
function is called with argument message the following steps
are taken:
"%ErrorPrototype%"
, «[[ErrorData]]»).message
", msgDesc).The value of the [[Prototype]] internal slot of the Error constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 1), the Error constructor has the
following properties:
The initial value of Error.prototype
is the intrinsic object %ErrorPrototype% (19.5.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Error prototype object is the intrinsic object %ErrorPrototype%. The Error prototype object is an ordinary object. It is not an Error instance and does not have an [[ErrorData]] internal slot.
The value of the [[Prototype]] internal slot of the Error prototype object is the intrinsic object %ObjectPrototype% (19.1.3).
The initial value of Error.prototype.constructor
is the intrinsic object %Error%.
The initial value of Error.prototype.message
is the empty String.
The initial value of Error.prototype.name
is "Error"
.
The following steps are taken:
"name"
)."Error"
; otherwise let name be ToString(name)."message"
).Error instances are ordinary objects that inherit properties from the Error prototype object and have an [[ErrorData]] internal slot whose value is undefined. The only specified uses of [[ErrorData]] is to identify Error and NativeError
instances as Error objects within Object.prototype.toString
.
A new instance of one of the NativeError objects below is thrown when a runtime error is detected. All of these objects share the same structure, as described in 19.5.6.
This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
Indicates a value that is not in the set or range of allowable values.
Indicate that an invalid reference value has been detected.
Indicates that a parsing error has occurred.
Indicates the actual type of an operand is different than the expected type.
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition.
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of the NativeError
objects defined in 19.5.5. Each of these objects has the
structure described below, differing only in the name used as the constructor name instead of NativeError, in the
name property of the prototype object, and in the implementation-defined message
property of the
prototype object.
For each error object, references to NativeError in the definition should be replaced with the appropriate error object name from 19.5.5.
When a NativeError constructor is called as a function rather than as a constructor, it creates and
initializes a new NativeError object. A call of the object as a function is equivalent to calling it as a
constructor with the same arguments. Thus the function call NativeError(…)
is
equivalent to the object creation expression new
NativeError(…)
with the same arguments.
Each NativeError constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
NativeError behaviour must include a super
call to the NativeError constructor to create and
initialize subclass instances with a [[ErrorData]] internal
slot.
When a NativeError function is called with argument message the following steps are taken:
"%NativeErrorPrototype%"
, «[[ErrorData]]» ).message
", msgDesc).The actual value of the string passed in step 2 is either "%EvalErrorPrototype%"
,
"%RangeErrorPrototype%"
, "%ReferenceErrorPrototype%"
, "%SyntaxErrorPrototype%"
,
"%TypeErrorPrototype%"
, or "%URIErrorPrototype%"
corresponding to which NativeError
constructor is being defined.
The value of the [[Prototype]] internal slot of a NativeError constructor is the intrinsic object %Error% (19.5.1).
Besides the length
property (whose value is 1), each NativeError constructor has the
following properties:
The initial value of NativeError.prototype
is a NativeError prototype object (19.5.6.3). Each NativeError constructor has a
distinct prototype object.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
Each NativeError prototype object is an ordinary object. It is not an Error instance and does not have an [[ErrorData]] internal slot.
The value of the [[Prototype]] internal slot of each NativeError prototype object is the intrinsic object %ErrorPrototype% (19.5.3).
The initial value of the constructor
property of the prototype for a given NativeError
constructor is the corresponding intrinsic object %NativeError% (19.5.6.1).
The initial value of the message
property of the prototype for a given NativeError constructor is
the empty String.
The initial value of the name
property of the prototype for a given NativeError constructor is a
string consisting of the name of the constructor (the name used instead of NativeError).
NativeError instances are ordinary objects that inherit properties from their NativeError prototype
object and have an [[ErrorData]] internal slot whose value
is undefined. The only specified use of [[ErrorData]] is by Object.prototype.toString
(19.1.3.6) to identify Error or NativeError instances.
The Number constructor is the %Number% intrinsic object and the initial value of the Number
property of
the global object. When called as a constructor, it creates and initializes a new Number object. When Number
is called as a function rather than as a constructor, it performs a type conversion.
The Number
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
Number
behaviour must include a super
call to the Number
constructor to create and
initialize the subclass instance with a [[NumberData]] internal
slot.
When Number
is called with argument number, the following steps are
taken:
"%NumberPrototype%"
, «[[NumberData]]» ).The value of the [[Prototype]] internal slot of the Number constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 1), the Number constructor has the following
properties:
The value of Number.EPSILON is the difference between 1 and the smallest value greater than 1 that is representable as a Number value, which is approximately 2.2204460492503130808472633361816 x 10−16.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
When the Number.isFinite
is called with one argument number, the following
steps are taken:
When the Number.isInteger
is called with one argument number, the
following steps are taken:
When the Number.isNaN
is called with one argument number, the following
steps are taken:
NOTE This function differs from the global isNaN function (18.2.3) is that it does not convert its argument to a Number before determining whether it is NaN.
When the Number.isSafeInteger
is called with one argument number, the
following steps are taken:
NOTE The value of Number.MAX_SAFE_INTEGER
is the largest integer n such that n
and n + 1 are both exactly representable as a Number value.
The value of Number.MAX_SAFE_INTEGER is 9007199254740991 (253−1).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]:
false }.
The value of Number.MAX_VALUE
is the largest positive finite value of the Number type, which is
approximately 1.7976931348623157 × 10308.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE The value of Number.MIN_SAFE_INTEGER
is the smallest integer n such that
n and n − 1 are both exactly representable as a Number value.
The value of Number.MIN_SAFE_INTEGER is −9007199254740991 (−(253−1)).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The value of Number.MIN_VALUE
is the smallest positive value of the Number type, which is approximately
5 × 10−324.
In the IEEE 754-2008 double precision binary representation, the smallest possible value is a denormalized number. If
an implementation does not support denormalized values, the value of Number.MIN_VALUE
must be the smallest
non-zero positive value that can actually be represented by the implementation.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The value of Number.NaN
is NaN.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The value of Number.NEGATIVE_INFINITY is −∞.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The value of the Number.parseFloat
data property is the same built-in function object that is the value of
the parseFloat
property of the global object defined in 18.2.4.
The value of the Number.parseInt
data property is the same built-in function object that is the value of
the parseInt
property of the global object defined in 18.2.5.
The value of Number.POSITIVE_INFINITY is +∞.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of Number.prototype
is the intrinsic object %NumberPrototype% (20.1.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Number prototype object is the intrinsic object %NumberPrototype%. The Number prototype object is an ordinary object. It is not a Number instance and does not have a [[NumberData]] internal slot.
The value of the [[Prototype]] internal slot of the Number prototype object is the intrinsic object %ObjectPrototype% (19.1.3).
Unless explicitly stated otherwise, the methods of the Number prototype object defined below are not generic and the this value passed to them must be either a Number value or an object that has a [[NumberData]] internal slot that has been initialized to a Number value.
The abstract operation thisNumberValue(value) performs the following steps:
The phrase “this Number value” within the specification of a method refers to the result returned by calling the abstract operation thisNumberValue with the this value of the method invocation passed as the argument.
The initial value of Number.prototype.constructor
is the intrinsic object %Number%.
Return a String containing this Number value represented in decimal exponential notation with one digit before the significand's decimal point and fractionDigits digits after the significand's decimal point. If fractionDigits is undefined, include as many significand digits as necessary to uniquely specify the Number (just like in ToString except that in this case the Number is always output in exponential notation). Specifically, perform the following steps:
"NaN"
."-"
."Infinity"
.toExponential
for values of f less than 0 or greater than 20. In this
case toExponential
would not necessarily throw RangeError for such values."."
, and b."+".
"0".
"+".
"-"
."e"
, c, and d.The length
property of the toExponential
method is 1.
If the toExponential
method is called with more than one argument, then the behaviour is undefined (see clause 17).
NOTE For implementations that provide more accurate conversions than required by the rules above, it is recommended that the following alternative version of step 12.b.i be used as a guideline:
i. Let e, n, and f be integers such that f ≥ 0, 10f ≤ n < 10f+1, the Number value for n × 10e–f is x, and f is as small as possible. If there are multiple possibilities for n, choose the value of n for which n × 10e–f is closest in value to x. If there are two such possible values of n, choose the one that is even.
NOTE 1 toFixed
returns a String containing this Number value represented in
decimal fixed-point notation with fractionDigits digits after the decimal point. If fractionDigits
is undefined, 0 is assumed.
The following steps are performed:
0
).toFixed
for values of f less than 0 or greater than 20. In this case
toFixed
would not necessarily throw RangeError for such values."NaN"
.-
"."0"
. Otherwise, let m be the String consisting
of the digits of the decimal representation of n (in order, with no leading zeroes)."."
, and b.The length
property of the toFixed
method is 1.
If the toFixed
method is called with more than one argument, then the behaviour is undefined (see clause 17).
NOTE 2 The output of toFixed
may be more precise than toString
for
some values because toString only prints enough significant digits to distinguish the number from adjacent number
values. For example,
(1000000000000000128).toString()
returns "1000000000000000100"
,
while(1000000000000000128).toFixed(0)
returns "1000000000000000128"
.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
Number.prototype.toLocaleString
method as specified in the ECMA-402 specification. If an ECMAScript
implementation does not include the ECMA-402 API the following specification of the toLocaleString
method is
used.
Produces a String value that represents this Number value formatted according to the conventions of the host
environment’s current locale. This function is implementation-dependent, and it is permissible, but not encouraged,
for it to return the same thing as toString
.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
The length
property of the toLocaleString
method is 0.
Return a String containing this Number value represented either in decimal exponential notation with one digit before the significand's decimal point and precision–1 digits after the significand's decimal point or in decimal fixed notation with precision significant digits. If precision is undefined, call ToString (7.1.12) instead. Specifically, perform the following steps:
"NaN"
."Infinity"
.toPrecision
for values of p less than 1 or greater than 21. In this
case toPrecision
would not necessarily throw RangeError for such values.The length
property of the toPrecision
method is 1.
If the toPrecision
method is called with more than one argument, then the behaviour is undefined (see clause 17).
NOTE The optional radix should be an integer value in the inclusive range 2 to 36. If radix not present or is undefined the Number 10 is used as the value of radix.
The following steps are performed:
a
-z
are used for digits with values 10 through 35. The precise algorithm is
implementation-dependent, however the algorithm should be a generalization of that specified in 7.1.12.1.The toString
function is not generic; it throws a TypeError exception if its this value is
not a Number or a Number object. Therefore, it cannot be transferred to other kinds of objects for use as a method.
Number instances are ordinary objects that inherit properties from the Number prototype object. Number instances also have a [[NumberData]] internal slot. The [[NumberData]] internal slot is the Number value represented by this Number object.
The Math object is the %Math% intrinsic object and the initial value of the Math
property of the global
object. The Math object is a single ordinary object.
The value of the [[Prototype]] internal slot of the Math object is the intrinsic object %ObjectPrototype% (19.1.3).
The Math object is not a function object. It does not have a [[Construct]] internal method; it is not possible to use the
Math object as a constructor with the new
operator. The Math object also does not have a [[Call]] internal
method; it is not possible to invoke the Math object as a function.
NOTE In this specification, the phrase “the Number value for x” has a technical meaning defined in 6.1.6.
The Number value for e, the base of the natural logarithms, which is approximately 2.7182818284590452354.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Number value for the natural logarithm of 10, which is approximately 2.302585092994046.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Number value for the natural logarithm of 2, which is approximately 0.6931471805599453.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Number value for the base-10 logarithm of e, the base of the natural logarithms; this value is approximately 0.4342944819032518.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE The value of Math.LOG10E
is approximately the reciprocal of the value of
Math.LN10
.
The Number value for the base-2 logarithm of e, the base of the natural logarithms; this value is approximately 1.4426950408889634.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE The value of Math.LOG2E
is approximately the reciprocal of the value of
Math.LN2
.
The Number value for π, the ratio of the circumference of a circle to its diameter, which is approximately 3.1415926535897932.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The Number value for the square root of ½, which is approximately 0.7071067811865476.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE The value of Math.SQRT1_2
is approximately the reciprocal of the value of
Math.SQRT2
.
The Number value for the square root of 2, which is approximately 1.4142135623730951.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of the @@toStringTag property is the String value "Math"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Each of the following Math
object functions applies the ToNumber abstract
operation to each of its arguments (in left-to-right order if there is more than one). If ToNumber returns an abrupt completion,
that Completion Record is immediately returned. Otherwise, the
function performs a computation on the resulting Number value(s). The value returned by each function is a Number.
In the function descriptions below, the symbols NaN, −0, +0, −∞ and +∞ refer to the Number values described in 6.1.6.
NOTE The behaviour of the functions acos
, acosh
, asin
,
asinh
, atan
, atanh
, atan2
, cbrt
, cos
,
cosh
, exp
, expm1
, hypot
, log
,log1p
,
log2
, log10
, pow
, random
, sin
, sinh
,
sqrt
, tan
, and tanh
is not precisely specified here except to require specific
results for certain argument values that represent boundary cases of interest. For other argument values, these
functions are intended to compute approximations to the results of familiar mathematical functions, but some latitude is
allowed in the choice of approximation algorithms. The general intent is that an implementer should be able to use the
same mathematical library for ECMAScript on a given hardware platform that is available to C programmers on that
platform.
Although the choice of algorithms is left to the implementation, it is recommended (but not specified by this
standard) that implementations use the approximation algorithms for IEEE 754-2008 arithmetic contained in
fdlibm
, the freely distributable mathematical library from Sun Microsystems (http://www.netlib.org/fdlibm)
.
Returns the absolute value of x; the result has the same magnitude as x but has positive sign.
Returns an implementation-dependent approximation to the arc cosine of x. The result is expressed in radians and ranges from +0 to +π.
Returns an implementation-dependent approximation to the inverse hyperbolic cosine of x.
Returns an implementation-dependent approximation to the arc sine of x. The result is expressed in radians and ranges from −π/2 to +π/2.
Returns an implementation-dependent approximation to the inverse hyperbolic sine of x.
Returns an implementation-dependent approximation to the arc tangent of x. The result is expressed in radians and ranges from −π/2 to +π/2.
Returns an implementation-dependent approximation to the inverse hyperbolic tangent of x.
Returns an implementation-dependent approximation to the arc tangent of the quotient y/x of the arguments y and x, where the signs of y and x are used to determine the quadrant of the result. Note that it is intentional and traditional for the two-argument arc tangent function that the argument named y be first and the argument named x be second. The result is expressed in radians and ranges from −π to +π.
Returns an implementation-dependent approximation to the cube root of x.
Returns the smallest (closest to −∞) Number value that is not less than x and is equal to a mathematical integer. If x is already an integer, the result is x.
The value of Math.ceil(x)
is the same as the value of -Math.floor(-x)
.
When Math.clz32
is called with one argument x, the following steps are
taken:
NOTE If n is 0, p will be 32. If the most significant bit of the 32-bit binary encoding of n is 1, p will be 0.
Returns an implementation-dependent approximation to the cosine of x. The argument is expressed in radians.
Returns an implementation-dependent approximation to the hyperbolic cosine of x.
NOTE The value of cosh(x) is the same as (exp(x) + exp(-x))/2.
Returns an implementation-dependent approximation to the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms).
Returns an implementation-dependent approximation to subtracting 1 from the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms). The result is computed in a way that is accurate even when the value of x is close 0.
Returns the greatest (closest to +∞) Number value that is not greater than x and is equal to a mathematical integer. If x is already an integer, the result is x.
When Math.fround
is called with argument x the following steps are taken:
Math.hypot
returns an implementation-dependent approximation of the square root of
the sum of squares of its arguments.
The length property of the hypot
function is 2.
NOTE Implementations should take care to avoid the loss of precision from overflows and underflows that are prone to occur in naive implementations when this function is called with two or more arguments.
When the Math.imul
is called with arguments x and y the
following steps are taken:
Returns an implementation-dependent approximation to the natural logarithm of x.
Returns an implementation-dependent approximation to the natural logarithm of 1 + x. The result is computed in a way that is accurate even when the value of x is close to zero.
Returns an implementation-dependent approximation to the base 10 logarithm of x.
Returns an implementation-dependent approximation to the base 2 logarithm of x.
Given zero or more arguments, calls ToNumber on each of the arguments and returns the largest of the resulting values.
If no arguments are given, the result is −∞.
If any value is NaN, the result is NaN.
The comparison of values to determine the largest value is done using the Abstract Relational Comparison algorithm (7.2.11) except that +0 is considered to be larger than −0.
The length
property of the max
method is 2.
Given zero or more arguments, calls ToNumber on each of the arguments and returns the smallest of the resulting values.
If no arguments are given, the result is +∞.
If any value is NaN, the result is NaN.
The comparison of values to determine the smallest value is done using the Abstract Relational Comparison algorithm (7.2.11) except that +0 is considered to be larger than −0.
The length
property of the min
method is 2.
Returns an implementation-dependent approximation to the result of raising x to the power y.
Returns a Number value with positive sign, greater than or equal to 0 but less than 1, chosen randomly or pseudo randomly with approximately uniform distribution over that range, using an implementation-dependent algorithm or strategy. This function takes no arguments.
Each Math.random
function created for distinct code Realms must produce a distinct sequence of values from
successive calls.
Returns the Number value that is closest to x and is equal to a mathematical integer. If two integer Number values are equally close to x, then the result is the Number value that is closer to +∞. If x is already an integer, the result is x.
NOTE 1 Math.round(3.5)
returns 4, but Math.round(–3.5)
returns –3.
NOTE 2 The value of Math.round(x)
is not always the same as the value of
Math.floor(x+0.5)
. When x
is −0 or is less than 0 but greater than or equal to
-0.5, Math.round(x)
returns −0, but Math.floor(x+0.5)
returns +0. Math.round(x)
may also differ from the value of Math.floor(x+0.5)
because of internal rounding when computing x+0.5
.
Returns the sign of the x, indicating whether x is positive, negative or zero.
Returns an implementation-dependent approximation to the sine of x. The argument is expressed in radians.
Returns an implementation-dependent approximation to the hyperbolic sine of x.
NOTE The value of sinh(x) is the same as (exp(x) - exp(-x))/2.
Returns an implementation-dependent approximation to the square root of x.
Returns an implementation-dependent approximation to the tangent of x. The argument is expressed in radians.
Returns an implementation-dependent approximation to the hyperbolic tangent of x.
NOTE The value of tanh(x) is the same as (exp(x) - exp(-x))/(exp(x) + exp(-x)).
Returns the integral part of the number x, removing any fractional digits. If x is already an integer, the result is x.
The following functions are abstract operations that operate on time values (defined in 20.3.1.1). Note that, in every case, if any argument to one of these functions is NaN, the result will be NaN.
A Date object contains a Number indicating a particular instant in time to within a millisecond. Such a Number is called a time value. A time value may also be NaN, indicating that the Date object does not represent a specific instant of time.
Time is measured in ECMAScript in milliseconds since 01 January, 1970 UTC. In time values leap seconds are ignored. It is assumed that there are exactly 86,400,000 milliseconds per day. ECMAScript Number values can represent all integers from –9,007,199,254,740,992 to 9,007,199,254,740,992; this range suffices to measure times to millisecond precision for any instant that is within approximately 285,616 years, either forward or backward, from 01 January, 1970 UTC.
The actual range of times supported by ECMAScript Date objects is slightly smaller: exactly –100,000,000 days to 100,000,000 days measured relative to midnight at the beginning of 01 January, 1970 UTC. This gives a range of 8,640,000,000,000,000 milliseconds to either side of 01 January, 1970 UTC.
The exact moment of midnight at the beginning of 01 January, 1970 UTC is represented by the value +0.
A given time value t belongs to day number
where the number of milliseconds per day is
The remainder is called the time within the day:
ECMAScript uses an extrapolated Gregorian system to map a day number to a year number and to determine the month and date within that year. In this system, leap years are precisely those which are (divisible by 4) and ((not divisible by 100) or (divisible by 400)). The number of days in year number y is therefore defined by
DaysInYear(y)
= 365 if (y modulo 4)
≠ 0
= 366 if (y modulo 4) = 0 and (y modulo 100) ≠ 0
= 365 if (y modulo 100) = 0 and (y modulo 400)
≠ 0
= 366 if (y modulo 400) = 0
All non-leap years have 365 days with the usual number of days per month and leap years have an extra day in February. The day number of the first day of year y is given by:
DayFromYear(y) = 365 × (y−1970) + floor((y−1969)/4) − floor((y−1901)/100) + floor((y−1601)/400)
The time value of the start of a year is:
TimeFromYear(y) = msPerDay × DayFromYear(y)
A time value determines a year by:
YearFromTime(t) = the largest integer y (closest to positive infinity) such that TimeFromYear(y) ≤ t
The leap-year function is 1 for a time within a leap year and otherwise is zero:
InLeapYear(t)
= 0 if DaysInYear(YearFromTime(t)) = 365
= 1 if
DaysInYear(YearFromTime(t)) = 366
Months are identified by an integer in the range 0 to 11, inclusive. The mapping MonthFromTime(t) from a time value t to a month number is defined by:
MonthFromTime(t)
= 0 if 0 ≤ DayWithinYear(t) <
31
= 1 if 31 ≤ DayWithinYear (t) < 59+InLeapYear(t)
= 2 if 59+InLeapYear(t)
≤ DayWithinYear (t) < 90+InLeapYear(t)
= 3 if 90+InLeapYear(t) ≤ DayWithinYear (t) < 120+InLeapYear(t)
= 4 if 120+InLeapYear(t) ≤ DayWithinYear (t) < 151+InLeapYear(t)
= 5 if 151+InLeapYear(t) ≤ DayWithinYear (t) < 181+InLeapYear(t)
= 6 if 181+InLeapYear(t) ≤ DayWithinYear (t) < 212+InLeapYear(t)
= 7 if 212+InLeapYear(t) ≤ DayWithinYear (t) < 243+InLeapYear(t)
= 8 if 243+InLeapYear(t) ≤ DayWithinYear (t) < 273+InLeapYear(t)
= 9 if 273+InLeapYear(t) ≤ DayWithinYear (t) < 304+InLeapYear(t)
= 10 if 304+InLeapYear(t) ≤ DayWithinYear (t) < 334+InLeapYear(t)
= 11 if 334+InLeapYear(t) ≤ DayWithinYear (t) < 365+InLeapYear(t)
where
DayWithinYear(t) = Day(t)−DayFromYear(YearFromTime(t))
A month value of 0 specifies January; 1 specifies February; 2 specifies March; 3 specifies April; 4 specifies May; 5 specifies June; 6 specifies July; 7 specifies August; 8 specifies September; 9 specifies October; 10 specifies November; and 11 specifies December. Note that MonthFromTime(0) = 0, corresponding to Thursday, 01 January, 1970.
A date number is identified by an integer in the range 1 through 31, inclusive. The mapping DateFromTime(t) from a time value t to a date number is defined by:
DateFromTime(t)
= DayWithinYear(t)+1 if MonthFromTime(t)=0
= DayWithinYear(t)−30 if MonthFromTime(t)=1
= DayWithinYear(t)−58−InLeapYear(t) if MonthFromTime(t)=2
= DayWithinYear(t)−89−InLeapYear(t) if MonthFromTime(t)=3
= DayWithinYear(t)−119−InLeapYear(t) if MonthFromTime(t)=4
= DayWithinYear(t)−150−InLeapYear(t) if MonthFromTime(t)=5
= DayWithinYear(t)−180−InLeapYear(t) if MonthFromTime(t)=6
= DayWithinYear(t)−211−InLeapYear(t) if MonthFromTime(t)=7
= DayWithinYear(t)−242−InLeapYear(t) if MonthFromTime(t)=8
= DayWithinYear(t)−272−InLeapYear(t) if MonthFromTime(t)=9
= DayWithinYear(t)−303−InLeapYear(t) if MonthFromTime(t)=10
= DayWithinYear(t)−333−InLeapYear(t) if MonthFromTime(t)=11
The weekday for a particular time value t is defined as
WeekDay(t) = (Day(t) + 4) modulo 7
A weekday value of 0 specifies Sunday; 1 specifies Monday; 2 specifies Tuesday; 3 specifies Wednesday; 4 specifies Thursday; 5 specifies Friday; and 6 specifies Saturday. Note that WeekDay(0) = 4, corresponding to Thursday, 01 January, 1970.
An implementation of ECMAScript is expected to determine the local time zone adjustment. The local time zone adjustment is a value LocalTZA measured in milliseconds which when added to UTC represents the local standard time. Daylight saving time is not reflected by LocalTZA.
NOTE It is recommended that implementations use the time zone information of the IANA Time Zone Database http://www.iana.org/time-zones/.
An implementation dependent algorithm using best available information on time zones to determine the local daylight saving time adjustment DaylightSavingTA(t), measured in milliseconds. An implementation of ECMAScript is expected to make its best effort to determine the local daylight saving time adjustment.
NOTE It is recommended that implementations use the time zone information of the IANA Time Zone Database http://www.iana.org/time-zones/.
The abstract operation LocalTime with argument t converts t from UTC to local time by performing the following steps:
The abstract operation UTC with argument t converts t from local time to UTC is defined by performing the following steps:
NOTE UTC(LocalTime(t)) is not necessarily always equal to t.
The following abstract operations are useful in decomposing time values:
HourFromTime(t) = floor(t / msPerHour) modulo HoursPerDay
MinFromTime(t) = floor(t / msPerMinute) modulo MinutesPerHour
SecFromTime(t) = floor(t / msPerSecond) modulo SecondsPerMinute
msFromTime(t) = t modulo msPerSecond
where
HoursPerDay = 24
MinutesPerHour = 60
SecondsPerMinute = 60
msPerSecond = 1000
msPerMinute = 60000 = msPerSecond × SecondsPerMinute
msPerHour = 3600000 = msPerMinute × MinutesPerHour
The abstract operation MakeTime calculates a number of milliseconds from its four arguments, which must be ECMAScript Number values. This operator functions as follows:
*
msPerHour
+
m *
msPerMinute
+
s *
msPerSecond
+
milli, performing the arithmetic according to IEEE 754-2008 rules (that is, as if using the
ECMAScript operators *
and +
).The abstract operation MakeDay calculates a number of days from its three arguments, which must be ECMAScript Number values. This operator functions as follows:
The abstract operation MakeDate calculates a number of milliseconds from its two arguments, which must be ECMAScript Number values. This operator functions as follows:
The abstract operation TimeClip calculates a number of milliseconds from its argument, which must be an ECMAScript Number value. This operator functions as follows:
NOTE The point of step 3 is that an implementation is permitted a choice of internal representations of time values, for example as a 64-bit signed integer or as a 64-bit floating-point value. Depending on the implementation, this internal representation may or may not distinguish −0 and +0.
ECMAScript defines a string interchange format for date-times based upon a simplification of the ISO 8601 Extended
Format. The format is as follows: YYYY-MM-DDTHH:mm:ss.sssZ
Where the fields are as follows:
YYYY |
is the decimal digits of the year 0000 to 9999 in the Gregorian calendar. |
- |
"-" (hyphen) appears literally twice in the string. |
MM |
is the month of the year from 01 (January) to 12 (December). |
DD |
is the day of the month from 01 to 31. |
T |
"T" appears literally in the string, to indicate the beginning of the time element. |
HH |
is the number of complete hours that have passed since midnight as two decimal digits from 00 to 24. |
: |
":" (colon) appears literally twice in the string. |
mm |
is the number of complete minutes since the start of the hour as two decimal digits from 00 to 59. |
ss |
is the number of complete seconds since the start of the minute as two decimal digits from 00 to 59. |
. |
"." (dot) appears literally in the string. |
sss |
is the number of complete milliseconds since the start of the second as three decimal digits. |
Z |
is the time zone offset specified as "Z" (for UTC) or either "+" or "-" followed by a time expression HH:mm |
This format includes date-only forms:
YYYY
YYYY-MM
YYYY-MM-DD
It also includes “date-time” forms that consist of one of the above date-only forms immediately followed by one of the following time forms with an optional time zone offset appended:
THH:mm
THH:mm:ss
THH:mm:ss.sss
All numbers must be base 10. If the MM
or
DD
fields are absent "01"
is used as the value. If the HH
, mm
, or
ss
fields are absent "00"
is used as the value and the value of an absent sss
field is "000"
. If the time zone offset is absent, the date-time is interpreted as a local time.
Illegal values (out-of-bounds as well as syntax errors) in a format string means that the format string is not a valid instance of this format.
NOTE 1 As every day both starts and ends with midnight, the two notations
00:00
and 24:00
are available to distinguish the two midnights that can be associated with
one date. This means that the following two notations refer to exactly the same point in time:
1995-02-04T24:00
and 1995-02-05T00:00
NOTE 2 There exists no international standard that specifies abbreviations for civil time zones like CET, EST, etc. and sometimes the same abbreviation is even used for two very different time zones. For this reason, ISO 8601 and this format specifies numeric representations of date and time.
ECMAScript requires the ability to specify 6 digit years (extended years); approximately 285,426 years, either forward or backward, from 01 January, 1970 UTC. To represent years before 0 or after 9999, ISO 8601 permits the expansion of the year representation, but only by prior agreement between the sender and the receiver. In the simplified ECMAScript format such an expanded year representation shall have 2 extra year digits and is always prefixed with a + or – sign. The year 0 is considered positive and hence prefixed with a + sign.
NOTE Examples of extended years:
-283457-03-21T15:00:59.008Z |
283458 B.C. |
-000001-01-01T00:00:00Z |
2 B.C. |
+000000-01-01T00:00:00Z |
1 B.C. |
+000001-01-01T00:00:00Z |
1 A.D. |
+001970-01-01T00:00:00Z |
1970 A.D. |
+002009-12-15T00:00:00Z |
2009 A.D. |
+287396-10-12T08:59:00.992Z |
287396 A.D. |
The Date constructor is the %Date% intrinsic object and the initial value of the Date
property of the
global object. When called as a constructor it creates and initializes a new Date object. When Date
is called
as a function rather than as a constructor, it returns a String representing the current time (UTC).
The Date
constructor is a single function whose behaviour is overloaded based upon the number and types of
its arguments.
The Date
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
Date
behaviour must include a super
call to the Date
constructor to create and
initialize the subclass instance with a [[DateValue]] internal
slot.
This description applies only if the Date constructor is called with at least two arguments.
When the Date
function is called the following steps are taken:
"%DatePrototype%"
, « [[DateValue]]»).This description applies only if the Date constructor is called with exactly one argument.
When the Date
function is called the following steps are taken:
parse
method (20.3.3.2). If the parse resulted in an abrupt completion, tv is the Completion Record."%DatePrototype%"
, « [[DateValue]]»).This description applies only if the Date constructor is called with no arguments.
When the Date
function is called the following steps are taken:
"%DatePrototype%"
, « [[DateValue]]»).The value of the [[Prototype]] internal slot of the Date constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 7
), the Date constructor has the following
properties:
The now
function returns a Number value that is the time
value designating the UTC date and time of the occurrence of the call to now
.
The parse
function applies the ToString operator to its argument. If ToString results in an abrupt completion
the Completion Record is immediately returned. Otherwise,
parse
interprets the resulting String as a date and time; it returns a Number, the UTC time value corresponding to the date and time. The String may be interpreted as
a local time, a UTC time, or a time in some other time zone, depending on the contents of the String. The function first
attempts to parse the format of the String according to the rules (including extended years) called out in Date Time
String Format (20.3.1.16). If the String does not conform to that format the
function may fall back to any implementation-specific heuristics or implementation-specific date formats. Unrecognizable
Strings or dates containing illegal element values in the format String shall cause Date.parse
to return
NaN.
If x is any Date object whose milliseconds amount is zero within a particular implementation of ECMAScript, then all of the following expressions should produce the same numeric value in that implementation, if all the properties referenced have their initial values:
x.valueOf()
Date.parse(x.toString())
Date.parse(x.toUTCString())
Date.parse(x.toISOString())
However, the expression
Date.parse(x.toLocaleString())
is not required to produce the same Number value as the preceding three expressions and, in general, the value produced
by Date.parse
is implementation-dependent when given any String value that does not conform to the Date Time
String Format (20.3.1.16) and that could not be produced in that implementation
by the toString
or toUTCString
method.
The initial value of Date.prototype
is the intrinsic object %DatePrototype% (20.3.4).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
When the UTC
function is called with fewer than two arguments, the behaviour is
implementation-dependent. When the UTC
function is called with two to seven arguments, it computes the date
from year, month and (optionally) date, hours, minutes,
seconds and ms. The following steps are taken:
The length
property of the UTC
function is 7.
NOTE The UTC
function differs from the Date
constructor in two
ways: it returns a time value as a Number, rather than creating a Date
object, and it interprets the arguments in UTC rather than as local time.
The Date prototype object is the intrinsic object %DatePrototype%. The Date prototype object is itself an ordinary object. It is not a Date instance and does not have a [[DateValue]] internal slot.
The value of the [[Prototype]] internal slot of the Date prototype object is the intrinsic object %ObjectPrototype% (20.3.4).
Unless explicitly defined otherwise, the methods of the Date prototype object defined below are not generic and the this value passed to them must be an object that has a [[DateValue]] internal slot that has been initialized to a time value.
The abstract operation thisTimeValue(value) performs the following steps:
In following descriptions of functions that are properties of the Date prototype object, the phrase “this Date object” refers to the object that is the this value for the invocation of the function. If the Type of the this value is not Object, a TypeError exception is thrown. The phrase “this time value” within the specification of a method refers to the result returned by calling the abstract operation thisTimeValue with the this value of the method invocation passed as the argument.
The initial value of Date.prototype.constructor
is the intrinsic object %Date%.
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The following steps are performed:
The length
property of the setFullYear
method is 3.
NOTE If month is not specified, this method behaves as if month were
specified with the value getMonth()
. If date is not specified, it behaves as if date
were specified with the value getDate()
.
The following steps are performed:
The length
property of the setHours
method is 4.
NOTE If min is not specified, this method behaves as if min were
specified with the value getMinutes()
. If sec is not specified, it behaves as if sec
were specified with the value getSeconds()
. If ms is not specified, it behaves as if
ms were specified with the value getMilliseconds()
.
The following steps are performed:
The following steps are performed:
The length
property of the setMinutes
method is 3.
NOTE If sec is not specified, this method behaves as if sec were
specified with the value getSeconds()
. If ms is not specified, this behaves as if ms
were specified with the value getMilliseconds()
.
The following steps are performed:
The length
property of the setMonth
method is 2.
NOTE If date is not specified, this method behaves as if date were
specified with the value getDate()
.
The following steps are performed:
The length
property of the setSeconds
method is 2.
NOTE If ms is not specified, this method behaves as if ms were
specified with the value getMilliseconds()
.
The following steps are performed:
The following steps are performed:
The length
property of the setUTCFullYear
method is 3.
NOTE If month is not specified, this method behaves as if month were
specified with the value getUTCMonth()
. If date is not specified, it behaves as if
date were specified with the value getUTCDate()
.
The following steps are performed:
The length
property of the setUTCHours
method is 4.
NOTE If min is not specified, this method behaves as if min were
specified with the value getUTCMinutes()
. If sec is not specified, it behaves as if
sec were specified with the value getUTCSeconds()
. If ms is not specified, it behaves
as if ms were specified with the value getUTCMilliseconds()
.
The following steps are performed:
The following steps are performed:
The length
property of the setUTCMinutes
method is 3.
NOTE If sec is not specified, this method behaves as if sec were
specified with the value getUTCSeconds()
. If ms is not specified, it function behaves as if
ms were specified with the value return by getUTCMilliseconds()
.
The following steps are performed:
The length
property of the setUTCMonth
method is 2.
NOTE If date is not specified, this method behaves as if date were
specified with the value getUTCDate()
.
The following steps are performed:
The length
property of the setUTCSeconds
method is 2.
NOTE If ms is not specified, this method behaves as if ms were
specified with the value getUTCMilliseconds()
.
This function returns a String value. The contents of the String are implementation-dependent, but are intended to represent the “date” portion of the Date in the current time zone in a convenient, human-readable form.
This function returns a String value representing the instance in time corresponding to this time value. The format of the String is the Date Time string format defined in 20.3.1.16. All fields are present in the String. The time zone is always UTC, denoted by the suffix Z. If this time value is not a finite Number or if the year is not a value that can be represented in that format (if necessary using extended year format), a RangeError exception is thrown.
This function provides a String representation of a Date object for use by JSON.stringify
(24.3.2).
When the toJSON
method is called with argument key, the following steps
are taken:
"toISOString"
).NOTE 1 The argument is ignored.
NOTE 2 The toJSON
function is intentionally generic; it does not require that
its this value be a Date object. Therefore, it can be transferred to other kinds of objects for use as a method.
However, it does require that any such object have a toISOString
method.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
Date.prototype.toLocaleDateString
method as specified in the ECMA-402 specification. If an ECMAScript
implementation does not include the ECMA-402 API the following specification of the toLocaleDateString
method is used.
This function returns a String value. The contents of the String are implementation-dependent, but are intended to represent the “date” portion of the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment’s current locale.
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
The length
property of the toLocaleDateString
method is 0.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
Date.prototype.toLocaleString
method as specified in the ECMA-402 specification. If an ECMAScript
implementation does not include the ECMA-402 API the following specification of the toLocaleString
method is
used.
This function returns a String value. The contents of the String are implementation-dependent, but are intended to represent the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment’s current locale.
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
The length
property of the toLocaleString
method is 0.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
Date.prototype.toLocaleTimeString
method as specified in the ECMA-402 specification. If an ECMAScript
implementation does not include the ECMA-402 API the following specification of the toLocaleTimeString
method is used.
This function returns a String value. The contents of the String are implementation-dependent, but are intended to represent the “time” portion of the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment’s current locale.
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
The length
property of the toLocaleTimeString
method is 0.
The following steps are performed:
NOTE 1 For any Date object d whose
milliseconds amount is zero, the result of Date.parse(d.toString())
is equal to d.valueOf()
. See 20.3.3.2.
NOTE 2 The toString
function is intentionally generic; it does not require
that its this value be a Date object. Therefore, it can be transferred to other kinds of objects for use as a
method.
The following steps are performed:
This function returns a String value. The contents of the String are implementation-dependent, but are intended to represent the “time” portion of the Date in the current time zone in a convenient, human-readable form.
This function returns a String value. The contents of the String are implementation-dependent, but are intended to represent this time value in a convenient, human-readable form in UTC.
NOTE The intent is to produce a String representation of a date that is more readable than
the format specified in 20.3.1.16. It is not essential that the chosen format
be unambiguous or easily machine parsable. If an implementation does not have a preferred human-readable format it is
recommended to use the format defined in 20.3.1.16 but with a space rather
than a "T"
used to separate the date and time elements.
The valueOf
function returns a Number, which is this time value.
This function is called by ECMAScript language operators to convert a Date object to a primitive value. The allowed
values for hint are "default"
, "number"
, and "string"
. Date objects,
are unique among built-in ECMAScript object in that they treat "default"
as being equivalent to
"string"
, All other built-in ECMAScript objects treat "default"
as being equivalent to
"number"
.
When the @@toPrimitive
method is called with argument hint, the following
steps are taken:
string
" or the String value "default
" , then
string
".number
", then
number
".The value of the name
property of this function is "[Symbol.toPrimitive]"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Date instances are ordinary objects that inherit properties from the Date prototype object. Date instances also have a [[DateValue]] internal slot. The [[DateValue]] internal slot is the time value represented by this Date object.
The String constructor is the %String% intrinsic object and the initial value of the String
property of
the global object. When called as a constructor it creates and initializes a new String object. When String
is called as a function rather than as a constructor, it performs a type conversion.
The String
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
String
behaviour must include a super
call to the String
constructor to create and
initialize the subclass instance with a [[StringData]] internal
slot.
When String
is called with argument value, the following steps are
taken:
""
."%StringPrototype%"
)).The length
property of the String
function is 1.
The value of the [[Prototype]] internal slot of the String constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 1), the String constructor has the following
properties:
The String.fromCharCode
function may be called with any number of arguments which
form the rest parameter codeUnits. The following steps are taken:
The length
property of the fromCharCode
function is 1.
The String.fromCodePoint
function may be called with any number of arguments which
form the rest parameter codePoints. The following steps are taken:
.
The length
property of the fromCodePoint
function is 1.
The initial value of String.prototype
is the intrinsic object %StringPrototype% (21.1.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The String.raw
function may be called with a variable number of arguments. The first
argument is template and the remainder of the arguments form the List substitutions. The following steps are taken:
"raw"
))."length"
)).The length
property of the raw
function is 1.
NOTE String.raw is intended for use as a tag function of a Tagged Template (12.3.7). When called as such, the first argument will be a well formed template object and the rest parameter will contain the substitution values.
The String prototype object is the intrinsic object %StringPrototype%. The String prototype object is itself an ordinary object. It is not a String instance and does not have a [[StringData]] internal slot.
The value of the [[Prototype]] internal slot of the String prototype object is the intrinsic object %ObjectPrototype% (19.1.3).
Unless explicitly stated otherwise, the methods of the String prototype object defined below are not generic and the this value passed to them must be either a String value or an object that has a [[StringData]] internal slot that has been initialized to a String value.
The abstract operation thisStringValue(value) performs the following steps:
The phrase “this String value” within the specification of a method refers to the result returned by calling the abstract operation thisStringValue with the this value of the method invocation passed as the argument.
NOTE 1 Returns a single element String containing the code unit at index pos in the String value resulting from converting this object to a String. If there is no element at that index, the result is the empty String. The result is a String value, not a String object.
If pos is a value of Number type that is an integer, then the result of
x.charAt(
pos)
is equal to the result of
x.substring(
pos,
pos+1)
.
When the charAt
method is called with one argument pos, the following
steps are taken:
NOTE 2 The charAt
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
NOTE 1 Returns a Number (a nonnegative integer less than 216) that is the code unit value of the string element at index pos in the String resulting from converting this object to a String. If there is no element at that index, the result is NaN.
When the charCodeAt
method is called with one argument pos, the following
steps are taken:
NOTE 2 The charCodeAt
function is intentionally generic; it does not require
that its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 Returns a nonnegative integer Number less than 1114112 (0x110000) that is the code point value of the UTF-16 encoded code point (6.1.4) starting at the string element at index pos in the String resulting from converting this object to a String. If there is no element at that index, the result is undefined. If a valid UTF-16 surrogate pair does not begin at pos, the result is the code unit at pos.
When the codePointAt
method is called with one argument pos, the following
steps are taken:
NOTE 2 The codePointAt
function is intentionally generic; it does not require
that its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 When the concat
method is called it returns a String consisting of the
code units of the this
object (converted to a String) followed by the code units of each of the arguments
converted to a String. The result is a String value, not a String object.
When the concat
method is called with zero or more arguments the following steps are
taken:
The length
property of the concat
method is 1.
NOTE 2 The concat
function is intentionally generic; it does not require that
its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a
method.
The initial value of String.prototype.constructor
is the intrinsic object %String%.
The following steps are taken:
The length property of the endsWith method is 1.
NOTE 1 Returns true if the sequence of elements of searchString converted to a String is the same as the corresponding elements of this object (converted to a String) starting at endPosition – length(this). Otherwise returns false.
NOTE 2 Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
NOTE 3 The endsWith function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.
The includes
method takes two arguments, searchString and position, and
performs the following steps:
The length property of the includes
method is 1.
NOTE 1 If searchString appears as a substring of the result of converting this object to a String, at one or more indices that are greater than or equal to position, return true; otherwise, returns false. If position is undefined, 0 is assumed, so as to search all of the String.
NOTE 2 Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
NOTE 3 The includes
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects
for use as a method.
NOTE 1 If searchString appears as a substring of the result of converting this
object to a String, at one or more indices that are greater than or equal to position, then the smallest such
index is returned; otherwise, ‑1
is returned. If position is undefined, 0 is
assumed, so as to search all of the String.
The indexOf
method takes two arguments, searchString and
position, and performs the following steps:
0
).-1
.The length
property of the indexOf
method is 1.
NOTE 2 The indexOf
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
NOTE 1 If searchString appears as a substring of the result of converting this
object to a String at one or more indices that are smaller than or equal to position, then the greatest such
index is returned; otherwise, ‑1
is returned. If position is undefined, the length
of the String value is assumed, so as to search all of the String.
The lastIndexOf
method takes two arguments, searchString and
position, and performs the following steps:
-1
.The length
property of the lastIndexOf
method is 1.
NOTE 2 The lastIndexOf
function is intentionally generic; it does not require
that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
localeCompare
method as specified in the ECMA-402 specification. If an ECMAScript implementation does not
include the ECMA-402 API the following specification of the localeCompare
method is used.
When the localeCompare
method is called with argument that, it returns a Number other than
NaN that represents the result of a locale-sensitive String comparison of the this value (converted to a
String) with that (converted to a String). The two Strings are S and That.
The two Strings are compared in an implementation-defined fashion. The result is intended to order String values in the
sort order specified by a host default locale, and will be negative, zero, or positive, depending on whether S
comes before That in the sort order, the Strings are equal, or S comes after That in the sort order, respectively.
Before performing the comparisons, the following steps are performed to prepare the Strings:
The meaning of the optional second and third parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not assign any other interpretation to those parameter positions.
The localeCompare
method, if considered as a function of two arguments this and that, is
a consistent comparison function (as defined in 22.1.3.24) on the set of all
Strings.
The actual return values are implementation-defined to permit implementers to encode additional information in the
value, but the function is required to define a total ordering on all Strings. This function must treat Strings that are
canonically equivalent according to the Unicode standard as identical and must return 0
when comparing
Strings that are considered canonically equivalent.
The length
property of the localeCompare
method is 1.
NOTE 1 The localeCompare
method itself is not directly suitable as an argument
to Array.prototype.sort
because the latter requires a function of
two arguments.
NOTE 2 This function is intended to rely on whatever language-sensitive comparison functionality is available to the ECMAScript environment from the host environment, and to compare according to the rules of the host environment’s current locale. However, regardless of the host provided comparison capabilities, this function must treat Strings that are canonically equivalent according to the Unicode standard as identical. It is recommended that this function should not honour Unicode compatibility equivalences or decompositions. For a definition and discussion of canonical equivalence see the Unicode Standard, chapters 2 and 3, as well as Unicode Standard Annex #15, Unicode Normalization Forms (http://www.unicode.org/reports/tr15/) and Unicode Technical Note #5, Canonical Equivalence in Applications (http://www.unicode.org/notes/tn5/). Also see Unicode Technical Standard #10, Unicode Collation Algorithm (http://www.unicode.org/reports/tr10/).
NOTE 3 The localeCompare
function is intentionally generic; it does not require
that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
When the match
method is called with argument regexp, the following steps
are taken:
NOTE The match
function is intentionally generic; it does not require that its
this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
When the normalize
method is called with one argument form, the following
steps are taken:
"NFC"
."NFC"
, "NFD"
,
"NFKC"
, or "NFKD"
, throw a RangeError exception.The length
property of the normalize
method is 0.
NOTE The normalize
function is intentionally generic; it does not require that
its this value be a String object. Therefore it can be transferred to other kinds of objects for use as a
method.
The following steps are taken:
NOTE 1 This method creates a String consisting of the code units of the this
object (converted to String) repeated count times.
NOTE 2 The repeat
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
When the replace
method is called with arguments searchValue and
replaceValue the following steps are taken:
NOTE The replace
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
The abstract operation GetSubstitution performs the following steps:
$
replacements are done left-to-right, and, once such a replacement is performed, the
new replacement text is not subject to further replacements.Code units | Unicode Characters | Replacement text |
---|---|---|
0x0024, 0x0024 | $$ |
$ |
0x0024, 0x0026 | $& |
matched |
0x0024, 0x0060 | $` |
If position is 0, the replacement is the empty String. Otherwise the replacement is the substring of str that starts at index 0 and whose last code unit is at index position -1. |
0x0024, 0x0027 | $' |
If tailPos ≥ stringLength, the replacement is the empty String. Otherwise the replacement is the substring of str that starts at index tailPos and continues to the end of str. |
0x0024, N Where 0x0031 ≤ N ≤ 0x0039 |
$n where is one of 1 2 3 4 5 6 7 8 9 and $n is not followed by a decimal digit |
The nth element of captures, where n is a single digit in the range 1 to 9. If n≤m and the nth element of captures is undefined, use the empty String instead. If n>m, the result is implementation-defined. |
0x0024, N, N Where 0x0030 ≤ N ≤ 0x0039 |
$nn where is one of 0 1 2 3 4 5 6 7 8 9 |
The nnth element of captures, where nn is a two-digit decimal number in the range 01 to 99. If nn≤m and the nnth element of captures is undefined, use the empty String instead. If nn is 00 or nn>m, the result is implementation-defined. |
0x0024 | $ in any context that does not match any of the above. |
$ |
When the search method is called with argument regexp, the following steps are taken:
NOTE The search
function is intentionally generic; it does not require that its
this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
The slice
method takes two arguments, start and end, and
returns a substring of the result of converting this object to a String, starting from index start and running
to, but not including, index end (or through the end of the String if end is undefined). If
start is negative, it is treated as sourceLength+start where sourceLength is the length of the String. If
end is negative, it is treated as sourceLength+end where sourceLength is the length of the String. The result is a
String value, not a String object. The following steps are taken:
The length
property of the slice
method is 2.
NOTE The slice
function is intentionally generic; it does not require that its
this value be a String object. Therefore it can be transferred to other kinds of objects for use as a method.
Returns an Array object into which substrings of the result of converting this object to a String have been stored. The substrings are determined by searching from left to right for occurrences of separator; these occurrences are not part of any substring in the returned array, but serve to divide up the String value. The value of separator may be a String of any length or it may be an object, such as an RegExp, that has a @@split method.
When the split
method is called, the following steps are taken:
"0"
,
S)."0"
,
S).The length
property of the split
method is 2.
NOTE 1 The value of separator may be an empty String, an empty regular
expression, or a regular expression that can match an empty String. In this case, separator does not match
the empty substring at the beginning or end of the input String, nor does it match the empty substring at the end of
the previous separator match. (For example, if separator is the empty String, the String is split up into
individual code unit elements; the length of the result array equals the length of the String, and each substring
contains one code unit.) If separator is a regular expression, only the first match at a given index of the
this String is considered, even if backtracking could yield a non-empty-substring match at that index. (For
example, "ab".split(/a*?/)
evaluates to the array ["a","b"]
, while
"ab".split(/a*/)
evaluates to the array["","b"]
.)
If the this object is (or converts to) the empty String, the result depends on whether separator can match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty String.
If separator is a regular expression that contains capturing parentheses, then each time separator is matched the results (including any undefined results) of the capturing parentheses are spliced into the output array. For example,
"A<B>bold</B>and<CODE>coded</CODE>".split(/<(\/)?([^<>]+)>/)
evaluates to the array:
["A", undefined, "B", "bold", "/", "B", "and",
undefined,
"CODE", "coded", "/", "CODE", ""]
If separator is undefined, then the result array contains just one String, which is the this value (converted to a String). If limit is not undefined, then the output array is truncated so that it contains no more than limit elements.
NOTE 2 The split
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
The abstract operation SplitMatch takes three parameters, a String S, an integer q, and a String R, and performs the following steps in order to return either false or the end index of a match:
The following steps are taken:
The length property of the startsWith method is 1.
NOTE 1 This method returns true if the sequence of elements of searchString converted to a String is the same as the corresponding elements of this object (converted to a String) starting at index position. Otherwise returns false.
NOTE 2 Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
NOTE 3 The startsWith function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.
The substring method takes two arguments, start and end, and returns a substring of the result of converting this object to a String, starting from index start and running to, but not including, index end of the String (or through the end of the String is end is undefined). The result is a String value, not a String object.
If either argument is NaN or negative, it is replaced with zero; if either argument is larger than the length of the String, it is replaced with the length of the String.
If start is larger than end, they are swapped.
The following steps are taken:
The length
property of the substring
method is 2.
NOTE The substring
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
toLocaleLowerCase
method as specified in the ECMA-402 specification. If an ECMAScript implementation does not
include the ECMA-402 API the following specification of the toLocaleLowerCase
method is used.
This function interprets a String value as a sequence of UTF-16 encoded code points, as described in 6.1.4.
This function works exactly the same as toLowerCase
except that its result is intended to yield the
correct result for the host environment’s current locale, rather than a locale-independent result. There will only
be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode
case mappings.
The length property of the toLocaleLowerCase method is 0.
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
NOTE The toLocaleLowerCase
function is intentionally generic; it does not
require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for
use as a method.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
toLocaleUpperCase
method as specified in the ECMA-402 specification. If an ECMAScript implementation does not
include the ECMA-402 API the following specification of the toLocaleUpperCase
method is used.
This function interprets a String value as a sequence of UTF-16 encoded code points, as described in 6.1.4.
This function works exactly the same as toUpperCase
except that its result is intended to yield the
correct result for the host environment’s current locale, rather than a locale-independent result. There will only
be a difference in the few cases (such as Turkish) where the rules for that language conflict with the regular Unicode
case mappings.
The length property of the toLocaleUpperCase method is 0.
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
NOTE The toLocaleUpperCase
function is intentionally generic; it does not
require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for
use as a method.
This function interprets a String value as a sequence of UTF-16 encoded code points, as described in 6.1.4. The following steps are taken:
The result must be derived according to the locale-insensitive case mappings in the Unicode Character Database (this explicitly includes not only the UnicodeData.txt file, but also all locale-insensitive mappings in the SpecialCasings.txt file that accompanies it).
NOTE 1 The case mapping of some code points may produce multiple code points . In this case
the result String may not be the same length as the source String. Because both toUpperCase
and
toLowerCase
have context-sensitive behaviour, the functions are not symmetrical. In other words,
s.toUpperCase().toLowerCase()
is not necessarily equal to s.toLowerCase()
.
NOTE 2 The toLowerCase
function is intentionally generic; it does not require
that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
When the toString
method is called, the following steps are taken:
NOTE For a String object, the toString
method happens to return the same thing
as the valueOf
method.
This function interprets a String value as a sequence of UTF-16 encoded code points, as described in 6.1.4.
This function behaves in exactly the same way as String.prototype.toLowerCase
, except that code points are mapped to
their uppercase equivalents as specified in the Unicode Character Database.
NOTE The toUpperCase
function is intentionally generic; it does not require that
its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
This function interprets a String value as a sequence of UTF-16 encoded code points, as described in 6.1.4.
The following steps are taken:
NOTE The trim
function is intentionally generic; it does not require that its
this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a
method.
When the valueOf
method is called, the following steps are taken:
When the @@iterator method is called it returns an Iterator object (25.1.1.2) that iterates over the code points of a String value, returning each code point as a String value. The following steps are taken:
The value of the name
property of this function is "[Symbol.iterator]"
.
String instances are String exotic objects and have the internal methods specified for such objects. String instances inherit properties from the String prototype object. String instances also have a [[StringData]] internal slot.
String instances have a length
property, and a set of enumerable properties with integer indexed
names.
The number of elements in the String value represented by this String object.
Once a String object is initialized, this property is unchanging. It has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
An String Iterator is an object, that represents a specific iteration over some specific String instance object. There is not a named constructor for String Iterator objects. Instead, String iterator objects are created by calling certain methods of String instance objects.
Several methods of String objects return Iterator objects. The abstract operation CreateStringIterator with argument string is used to create such iterator objects. It performs the following steps:
All String Iterator Objects inherit properties from the %StringIteratorPrototype% intrinsic object. The %StringIteratorPrototype% object is an ordinary object and its [[Prototype]] internal slot is the %IteratorPrototype% intrinsic object (25.1.2). In addition, %StringIteratorPrototype% has the following properties:
The initial value of the @@toStringTag property is the String value "String Iterator"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
String Iterator instances are ordinary objects that inherit properties from the %StringIteratorPrototype% intrinsic object. String Iterator instances are initially created with the internal slots listed in Table 46.
Internal Slot | Description |
---|---|
[[IteratedString]] | The String value whose elements are being iterated. |
[[StringIteratorNextIndex]] | The integer index of the next string index to be examined by this iteration. |
A RegExp object contains a regular expression and the associated flags.
NOTE The form and functionality of regular expressions is modelled after the regular expression facility in the Perl 5 programming language.
The RegExp
constructor applies the following grammar to the input pattern String. An error occurs if the
grammar cannot interpret the String as an expansion of Pattern.
|
Disjunction[?U]^
$
\
b
\
B
(
?
=
Disjunction[?U] )
(
?
!
Disjunction[?U] )
?
*
+
?
{
DecimalDigits }
{
DecimalDigits ,
}
{
DecimalDigits ,
DecimalDigits }
.
\
AtomEscape[?U](
Disjunction[?U] )
(
?
:
Disjunction[?U] )
^
$
\
.
*
+
?
(
)
[
]
{
}
|
c
ControlLetterf
n
r
t
v
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
u
LeadSurrogate \u
TrailSurrogateu
LeadSurrogateu
TrailSurrogateu
NonSurrogateu
Hex4Digitsu{
HexDigits }
Each \u
TrailSurrogate for which the choice of associated u
LeadSurrogate is ambiguous shall be associated with the nearest possible u
LeadSurrogate that would otherwise have no corresponding \u
TrailSurrogate.
/
d
D
s
S
w
W
[
[lookahead ∉ {^
}] ClassRanges[?U] ]
[
^
ClassRanges[?U] ]
-
ClassAtom[?U] ClassRanges[?U]-
ClassAtom[?U] ClassRanges[?U]-
\
or ]
or -
\
ClassEscape[?U]b
-
u{
HexDigits }
A regular expression pattern is converted into an internal procedure using the process described below. An implementation is encouraged to use more efficient algorithms than the ones listed below, as long as the results are the same. The internal procedure is used as the value of a RegExp object’s [[RegExpMatcher]] internal slot.
A Pattern is either a BMP pattern or a Unicode pattern depending upon whether or not its
associated flags contain a "u"
. A BMP pattern matches against a String interpreted as consisting of a
sequence of 16-bit values that are Unicode code points in the range of the Basic Multilingual Plane. A Unicode pattern
matches against a String interpreted as consisting of Unicode code points encoded using UTF-16. In the context of
describing the behaviour of a BMP pattern “character” means a single 16-bit Unicode BMP code point. In the
context of describing the behaviour of a Unicode pattern “character” means a UTF-16 encoded code point (6.1.4). In either context, “character value” means the
numeric value of the corresponding non-encoded code point.
The syntax and semantics of Pattern is defined as if the source code for the Pattern was a List of SourceCharacter values where each SourceCharacter corresponds to a Unicode code point. If a BMP pattern contains a non-BMP SourceCharacter the entire pattern is encoded using UTF-16 and the individual code units of that encoding are used as the elements of the List.
NOTE For example, consider a pattern expressed in source text as the single non-BMP character U+1D11E (MUSICAL SYMBOL G CLEF). Interpreted as a Unicode pattern, it would be a single element (character) List consisting of the single code point 0x1D11E. However, interpreted as a BMP pattern, it is first UTF-16 encoded to produce a two element List consisting of the code units 0xD834 and 0xDD1E.
Patterns are passed to the RegExp constructor as ECMAScript String values in which non-BMP characters are UTF-16 encoded. For example, the single character MUSICAL SYMBOL G CLEF pattern, expressed as a String value, is a String of length 2 whose elements were the code units 0xD834 and 0xDD1E. So no further translation of the string would be necessary to process it as a BMP pattern consisting of two pattern characters. However, to process it as a Unicode pattern UTF16Decode (see 10.1.2) must be used in producing a List consisting of a single pattern character, the code point U+1D11E.
An implementation may not actually perform such translations to or from UTF-16, but the semantics of this specification requires that the result of pattern matching be as if such translations were performed.
The descriptions below use the following variables:
Input is a List consisting of all of the characters, in order, of the String being matched by the regular expression pattern. Each character is either a code unit or a code point, depending upon the kind of pattern involved. The notation Input[n] means the nth character of Input, where n can range between 0 (inclusive) and InputLength (exclusive).
InputLength is the number of characters in Input.
NcapturingParens is the total number of left capturing parentheses (i.e. the total number
of times the Atom :: (
Disjunction )
production is expanded) in the pattern. A left
capturing parenthesis is any (
pattern character that is matched by the (
terminal of the
Atom :: (
Disjunction )
production.
IgnoreCase is true if the RegExp object's [[OriginalFlags]] internal slot contains "i"
and otherwise is
false.
Multiline is true if the RegExp object’s [[OriginalFlags]] internal slot contains "m"
and otherwise is
false.
Unicode is true if the RegExp object’s [[OriginalFlags]] internal slot contains "u"
and otherwise is
false.
Furthermore, the descriptions below use the following internal data structures:
A CharSet is a mathematical set of characters, either code units or code points depending up the state of the Unicode flag. “All characters” means either all code unit values or all code point values also depending upon the state if Unicode.
A State is an ordered pair (endIndex, captures) where endIndex is an integer and captures is a List of NcapturingParens values. States are used to represent partial match states in the regular expression matching algorithms. The endIndex is one plus the index of the last input character matched so far by the pattern, while captures holds the results of capturing parentheses. The nth element of captures is either a List that represents the value obtained by the nth set of capturing parentheses or undefined if the nth set of capturing parentheses hasn’t been reached yet. Due to backtracking, many States may be in use at any time during the matching process.
A MatchResult is either a State or the special token failure that indicates that the match failed.
A Continuation procedure is an internal closure (i.e. an internal procedure with some arguments already bound to values) that takes one State argument and returns a MatchResult result. If an internal closure references variables which are bound in the function that creates the closure, the closure uses the values that these variables had at the time the closure was created. The Continuation attempts to match the remaining portion (specified by the closure's already-bound arguments) of the pattern against Input, starting at the intermediate state given by its State argument. If the match succeeds, the Continuation returns the final State that it reached; if the match fails, the Continuation returns failure.
A Matcher procedure is an internal closure that takes two arguments — a State and a Continuation — and returns a MatchResult result. A Matcher attempts to match a middle subpattern (specified by the closure's already-bound arguments) of the pattern against Input, starting at the intermediate state given by its State argument. The Continuation argument should be a closure that matches the rest of the pattern. After matching the subpattern of a pattern to obtain a new State, the Matcher then calls Continuation on that new State to test if the rest of the pattern can match as well. If it can, the Matcher returns the State returned by Continuation; if not, the Matcher may try different choices at its choice points, repeatedly calling Continuation until it either succeeds or all possibilities have been exhausted.
An AssertionTester procedure is an internal closure that takes a State argument and returns a Boolean result. The assertion tester tests a specific condition (specified by the closure's already-bound arguments) against the current place in Input and returns true if the condition matched or false if not.
An EscapeValue is either a character or an integer. An EscapeValue is used to denote the interpretation of a DecimalEscape escape sequence: a character ch means that the escape sequence is interpreted as the character ch, while an integer n means that the escape sequence is interpreted as a backreference to the nth set of capturing parentheses.
The production Pattern :: Disjunction evaluates as follows:
NOTE A Pattern evaluates (“compiles”) to an internal procedure value. RegExp.prototype.exec
and other methods can then apply this procedure to a
String and an offset within the String to determine whether the pattern would match starting at exactly that offset
within the String, and, if it does match, what the values of the capturing parentheses would be. The algorithms in 21.2.2 are designed so that compiling a pattern may throw a SyntaxError
exception; on the other hand, once the pattern is successfully compiled, applying the resulting internal procedure to
find a match in a String cannot throw an exception (except for any host-defined exceptions that can occur anywhere such
as out-of-memory).
The production Disjunction :: Alternative evaluates by evaluating Alternative to obtain a Matcher and returning that Matcher.
The production Disjunction ::
Alternative |
Disjunction evaluates as
follows:
NOTE The |
regular expression operator separates two alternatives. The pattern
first tries to match the left Alternative (followed by the sequel of the regular expression); if
it fails, it tries to match the right Disjunction (followed by the sequel of the regular
expression). If the left Alternative, the right Disjunction, and the
sequel all have choice points, all choices in the sequel are tried before moving on to the next choice in the left Alternative. If choices in the left Alternative are exhausted, the right Disjunction is tried instead of the left Alternative. Any capturing
parentheses inside a portion of the pattern skipped by |
produce undefined values instead of
Strings. Thus, for example,
/a|ab/.exec("abc")
returns the result "a"
and not "ab"
. Moreover,
/((a)|(ab))((c)|(bc))/.exec("abc")
returns the array
["abc", "a", "a", undefined, "bc", undefined, "bc"]
and not
["abc", "ab", undefined, "ab", "c", "c", undefined]
The production Alternative :: [empty] evaluates by returning a Matcher that takes two arguments, a State x and a Continuation c, and returns the result of calling c(x).
The production Alternative :: Alternative Term evaluates as follows:
NOTE Consecutive Terms try to simultaneously match consecutive portions of Input. If the left Alternative, the right Term, and the sequel of the regular expression all have choice points, all choices in the sequel are tried before moving on to the next choice in the right Term, and all choices in the right Term are tried before moving on to the next choice in the left Alternative.
The production Term :: Assertion evaluates by returning an internal Matcher closure that takes two arguments, a State x and a Continuation c, and performs the following steps when evaluated:
The production Term :: Atom evaluates as follows:
The production Term :: Atom Quantifier evaluates as follows:
(
Disjunction )
production is expanded prior to this production's
Term plus the total number of Atom ::
(
Disjunction )
productions enclosing
this Term.(
Disjunction )
productions enclosed by this production's Atom.The abstract operation RepeatMatcher takes eight parameters, a Matcher m, an integer min, an integer (or ∞) max, a Boolean greedy, a State x, a Continuation c, an integer parenIndex, and an integer parenCount, and performs the following steps:
NOTE 1 An Atom followed by a Quantifier is repeated the number of times specified by the Quantifier. A Quantifier can be non-greedy, in which case the Atom pattern is repeated as few times as possible while still matching the sequel, or it can be greedy, in which case the Atom pattern is repeated as many times as possible while still matching the sequel. The Atom pattern is repeated rather than the input character sequence that it matches, so different repetitions of the Atom can match different input substrings.
NOTE 2 If the Atom and the sequel of the regular expression all have choice points, the Atom is first matched as many (or as few, if non-greedy) times as possible. All choices in the sequel are tried before moving on to the next choice in the last repetition of Atom. All choices in the last (nth) repetition of Atom are tried before moving on to the next choice in the next-to-last (n–1)st repetition of Atom; at which point it may turn out that more or fewer repetitions of Atom are now possible; these are exhausted (again, starting with either as few or as many as possible) before moving on to the next choice in the (n-1)st repetition of Atom and so on.
Compare
/a[a-z]{2,4}/.exec("abcdefghi")
which returns "abcde"
with
/a[a-z]{2,4}?/.exec("abcdefghi")
which returns "abc"
.
Consider also
/(aa|aabaac|ba|b|c)*/.exec("aabaac")
which, by the choice point ordering above, returns the array
["aaba", "ba"]
and not any of:
["aabaac", "aabaac"]
["aabaac", "c"]
The above ordering of choice points can be used to write a regular expression that calculates the greatest common divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:
"aaaaaaaaaa,aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/,"$1")
which returns the gcd in unary notation "aaaaa"
.
NOTE 3 Step 5 of the RepeatMatcher clears Atom's captures each time Atom is repeated. We can see its behaviour in the regular expression
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")
which returns the array
["zaacbbbcac", "z", "ac", "a", undefined, "c"]
and not
["zaacbbbcac", "z", "ac", "a", "bbb", "c"]
because each iteration of the outermost *
clears all captured Strings contained in the quantified
Atom, which in this case includes capture Strings numbered 2, 3, 4, and 5.
NOTE 4 Step 1 of the RepeatMatcher's d closure states that, once the minimum number of repetitions has been satisfied, any more expansions of Atom that match the empty character sequence are not considered for further repetitions. This prevents the regular expression engine from falling into an infinite loop on patterns such as:
/(a*)*/.exec("b")
or the slightly more complicated:
/(a*)b\1+/.exec("baaaac")
which returns the array
["b", ""]
The production Assertion ::
^
evaluates by returning an internal AssertionTester closure that takes a State argument
x and performs the following steps when evaluated:
NOTE Even when the y
flag is used with a pattern, ^
always
matches only at the beginning of Input, or (if Multiline is true) at the beginning of a line.
The production Assertion ::
$
evaluates by returning an internal AssertionTester closure that takes a State argument
x and performs the following steps when evaluated:
The production Assertion ::
\
b
evaluates by returning an internal AssertionTester closure that
takes a State argument x and performs the following steps when evaluated:
The production Assertion ::
\
B
evaluates by returning an internal AssertionTester closure that
takes a State argument x and performs the following steps when evaluated:
The production Assertion ::
(
?
=
Disjunction )
evaluates as follows:
The production Assertion ::
(
?
!
Disjunction )
evaluates as follows:
The abstract operation IsWordChar takes an integer parameter e and performs the following steps:
a |
b |
c |
d |
e |
f |
g |
h |
i |
j |
k |
l |
m |
n |
o |
p |
q |
r |
s |
t |
u |
v |
w |
x |
y |
z |
A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L |
M |
N |
O |
P |
Q |
R |
S |
T |
U |
V |
W |
X |
Y |
Z |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
_ |
The production Quantifier :: QuantifierPrefix evaluates as follows:
The production Quantifier ::
QuantifierPrefix ?
evaluates as follows:
The production QuantifierPrefix :: *
evaluates as follows:
The production QuantifierPrefix :: +
evaluates as follows:
The production QuantifierPrefix :: ?
evaluates as follows:
The production QuantifierPrefix :: {
DecimalDigits }
evaluates as follows:
The production QuantifierPrefix :: {
DecimalDigits ,
}
evaluates as follows:
The production QuantifierPrefix :: {
DecimalDigits ,
DecimalDigits }
evaluates as follows:
The production Atom :: PatternCharacter evaluates as follows:
The production Atom :: .
evaluates as follows:
The production Atom :: \
AtomEscape evaluates as follows:
The production Atom :: CharacterClass evaluates as follows:
The production Atom :: (
Disjunction )
evaluates as follows:
(
Disjunction )
production is expanded prior to this production's
Atom plus the total number of Atom ::
(
Disjunction )
productions enclosing
this Atom.The production Atom :: (
?
:
Disjunction )
evaluates as follows:
The abstract operation CharacterSetMatcher takes two arguments, a CharSet A and a Boolean flag invert, and performs the following steps:
The abstract operation Canonicalize takes a character parameter ch and performs the following steps:
String.prototype.toUpperCase
using s as the
this value.NOTE 1 Parentheses of the form (
Disjunction
)
serve both to group the components of the Disjunction pattern together and to
save the result of the match. The result can be used either in a backreference (\
followed by a nonzero
decimal number), referenced in a replace String, or returned as part of an array from the regular expression matching
internal procedure. To inhibit the capturing behaviour of parentheses, use the form (?:
Disjunction )
instead.
NOTE 2 The form (?=
Disjunction )
specifies a zero-width positive lookahead. In order for it to succeed, the pattern inside Disjunction must match at the current position, but the current position is not advanced before
matching the sequel. If Disjunction can match at the current position in several ways, only
the first one is tried. Unlike other regular expression operators, there is no backtracking into a (?=
form (this unusual behaviour is inherited from Perl). This only matters when the Disjunction
contains capturing parentheses and the sequel of the pattern contains backreferences to those captures.
For example,
/(?=(a+))/.exec("baaabac")
matches the empty String immediately after the first b
and therefore returns the array:
["", "aaa"]
To illustrate the lack of backtracking into the lookahead, consider:
/(?=(a+))a*b\1/.exec("baaabac")
This expression returns
["aba", "a"]
and not:
["aaaba", "a"]
NOTE 3 The form (?!
Disjunction )
specifies a zero-width negative lookahead. In order for it to succeed, the pattern inside Disjunction must fail to match at the current position. The current position is not advanced before
matching the sequel. Disjunction can contain capturing parentheses, but backreferences to them
only make sense from within Disjunction itself. Backreferences to these capturing parentheses
from elsewhere in the pattern always return undefined because the negative lookahead must fail for the pattern
to succeed. For example,
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")
looks for an a
not immediately followed by some positive number n of a
's, a
b
, another n a
's (specified by the first \2
) and a c
. The second
\2
is outside the negative lookahead, so it matches against undefined and therefore always
succeeds. The whole expression returns the array:
["baaabaac", "ba", undefined, "abaac"]
NOTE 4 In case-insignificant matches when Unicode is true, all characters are implicitly case-folded using the simple mapping provided by the Unicode
standard immediately before they are compared. The simple mapping always maps to a single code point, so it does not
map, for example, "ß"
(U+00DF) to "SS"
. It may however map a code point outside the
Basic Latin range to a character within, for example, "
ſ"
(U+017F) to
"
s"
. Such characters are not mapped if Unicode is false. This prevents Unicode code points such as U+017F and U+212A from matching regular
expressions such as /[a‑z]/i
, but they will match /[a‑z]/ui
.
The production AtomEscape :: DecimalEscape evaluates as follows:
The production AtomEscape :: CharacterEscape evaluates as follows:
The production AtomEscape :: CharacterClassEscape evaluates as follows:
NOTE An escape sequence of the form \
followed by a nonzero decimal number
n matches the result of the nth set of capturing parentheses (see 0). It is an error if the
regular expression has fewer than n capturing parentheses. If the regular expression has n or more
capturing parentheses but the nth one is undefined because it has not captured anything, then the
backreference always succeeds.
The production CharacterEscape :: ControlEscape evaluates by returning the character according to Table 47.
ControlEscape | Character Value | Code Point | Unicode Name | Symbol |
---|---|---|---|---|
t |
9 | U+0009 |
CHARACTER TABULATION | <HT> |
n |
10 | U+000A |
LINE FEED (LF) | <LF> |
v |
11 | U+000B |
LINE TABULATION | <VT> |
f |
12 | U+000C |
FORM FEED (FF) | <FF> |
r |
13 | U+000D |
CARRIAGE RETURN (CR) | <CR> |
The production CharacterEscape :: c
ControlLetter evaluates as follows:
The production CharacterEscape :: HexEscapeSequence evaluates as follows:
The production CharacterEscape :: RegExpUnicodeEscapeSequence evaluates as follows:
The production CharacterEscape :: IdentityEscape evaluates as follows:
The production RegExpUnicodeEscapeSequence :: u
LeadSurrogate \u
TrailSurrogate evaluates as follows:
The production RegExpUnicodeEscapeSequence :: u
LeadSurrogate evaluates as follows:
The production RegExpUnicodeEscapeSequence :: u
TrailSurrogate evaluates as follows:
The production RegExpUnicodeEscapeSequence :: u
NonSurrogate evaluates as follows:
The production RegExpUnicodeEscapeSequence :: u
Hex4Digits evaluates as follows:
The production RegExpUnicodeEscapeSequence :: u{
HexDigits }
evaluates as follows:
The production LeadSurrogate :: Hex4Digits evaluates as follows:
The production TrailSurrogate :: Hex4Digits evaluates as follows:
The production NonSurrogate :: Hex4Digits evaluates as follows:
The production DecimalEscape :: DecimalIntegerLiteral evaluates as follows:
The definition of “the MV of DecimalIntegerLiteral” is in 11.8.3.
NOTE If \
is followed by a decimal number n whose first digit is not
0
, then the escape sequence is considered to be a backreference. It is an error if n is greater
than the total number of left capturing parentheses in the entire regular expression. \0
represents the
<NUL> character and cannot be followed by a decimal digit.
The production CharacterClassEscape :: d
evaluates by returning the ten-element set of characters containing the characters
0
through 9
inclusive.
The production CharacterClassEscape :: D
evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: d
.
The production CharacterClassEscape :: s
evaluates by returning the set of characters containing the characters that are on the
right-hand side of the WhiteSpace (11.2) or LineTerminator (11.3) productions.
The production CharacterClassEscape :: S
evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: s
.
The production CharacterClassEscape :: w
evaluates by returning the set of characters containing the sixty-three characters:
a |
b |
c |
d |
e |
f |
g |
h |
i |
j |
k |
l |
m |
n |
o |
p |
q |
r |
s |
t |
u |
v |
w |
x |
y |
z |
A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L |
M |
N |
O |
P |
Q |
R |
S |
T |
U |
V |
W |
X |
Y |
Z |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
_ |
The production CharacterClassEscape :: W
evaluates by returning the set of all characters not included in the set returned by CharacterClassEscape :: w
.
The production CharacterClass :: [
ClassRanges ]
evaluates by evaluating ClassRanges to obtain a CharSet and returning that CharSet and the Boolean false.
The production CharacterClass :: [
^
ClassRanges ]
evaluates
by evaluating ClassRanges to obtain a CharSet and returning that CharSet and the Boolean
true.
The production ClassRanges :: [empty] evaluates by returning the empty CharSet.
The production ClassRanges :: NonemptyClassRanges evaluates by evaluating NonemptyClassRanges to obtain a CharSet and returning that CharSet.
The production NonemptyClassRanges :: ClassAtom evaluates as follows:
The production NonemptyClassRanges :: ClassAtom NonemptyClassRangesNoDash evaluates as follows:
The production NonemptyClassRanges :: ClassAtom -
ClassAtom ClassRanges evaluates as follows:
The abstract operation CharacterRange takes two CharSet parameters A and B and performs the following steps:
The production NonemptyClassRangesNoDash :: ClassAtom evaluates as follows:
The production NonemptyClassRangesNoDash :: ClassAtomNoDash NonemptyClassRangesNoDash evaluates as follows:
The production NonemptyClassRangesNoDash :: ClassAtomNoDash -
ClassAtom
ClassRanges evaluates as follows:
NOTE 1 ClassRanges can expand into a single ClassAtom and/or ranges of two ClassAtom separated by dashes. In the latter case the ClassRanges includes all characters between the first ClassAtom and the second ClassAtom, inclusive; an error occurs if either ClassAtom does not represent a single character (for example, if one is \w) or if the first ClassAtom's character value is greater than the second ClassAtom's character value.
NOTE 2 Even if the pattern ignores case, the case of the two ends of a range is significant
in determining which characters belong to the range. Thus, for example, the pattern /[E-F]/i
matches only
the letters E
, F
, e
, and f
, while the pattern /[E-f]/i
matches all upper and lower-case letters in the Unicode Basic Latin block as well as the symbols [
,
\
, ]
, ^
, _
, and `
.
NOTE 3 A -
character can be treated literally or it can denote a range. It is
treated literally if it is the first or last character of ClassRanges, the beginning or end
limit of a range specification, or immediately follows a range specification.
The production ClassAtom :: -
evaluates by returning the CharSet containing the one character -
.
The production ClassAtom :: ClassAtomNoDash evaluates by evaluating ClassAtomNoDash to obtain a CharSet and returning that CharSet.
The production ClassAtomNoDash :: SourceCharacter but not one of \
or ]
or -
evaluates as follows:
The production ClassAtomNoDash :: \
ClassEscape evaluates as follows:
The production ClassEscape :: DecimalEscape evaluates as follows:
The production ClassEscape ::
b
evaluates as follows:
The production ClassEscape ::
-
evaluates as follows:
The production ClassEscape :: CharacterEscape evaluates as follows:
The production ClassEscape :: CharacterClassEscape evaluates as follows:
NOTE A ClassAtom can use any of the escape sequences that are allowed
in the rest of the regular expression except for \b
, \B
, and backreferences. Inside a CharacterClass, \b
means the backspace character, while \B
and
backreferences raise errors. Using a backreference inside a ClassAtom causes an error.
The RegExp constructor is the %RegExp% intrinsic object and the initial value of the RegExp
property of
the global object. When RegExp
is called as a function rather than as a constructor, it creates and
initializes a new RegExp object. Thus the function call RegExp(…)
is equivalent to the
object creation expression new RegExp(…)
with the same arguments.
The RegExp
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
RegExp
behaviour must include a super
call to the RegExp
constructor to create and
initialize subclass instances with the necessary internal slots.
The following steps are taken:
"constructor"
)."source"
)."flags"
).NOTE If pattern is supplied using a StringLiteral, the usual escape sequence substitutions are performed before the String is processed by RegExp. If pattern must contain an escape sequence to be recognized by RegExp, any U+005C (REVERSE SOLIDUS) code points must be escaped within the StringLiteral to prevent them being removed when the contents of the StringLiteral are formed.
When the abstract operation RegExpAlloc with argument newTarget is called, the following steps are taken:
"%RegExpPrototype%"
, «[[RegExpMatcher]], [[OriginalSource]],
[[OriginalFlags]]»)."lastIndex"
, PropertyDescriptor {[[Writable]]: true, [[Enumerable]]: false,
[[Configurable]]: false}).When the abstract operation RegExpInitialize with arguments obj, pattern, and flags is called, the following steps are taken:
"g"
, "i"
, "m"
,
"u"
, or "y"
or if it contains the same code unit more than once, throw a
SyntaxError exception."u"
, let BMP be false; else let BMP be true."lastIndex"
, 0,
true).When the abstract operation RegExpCreate with arguments P and F is called, the following steps are taken:
When the abstract operation EscapeRegExpPattern with arguments P and F is called, the following occurs:
"u"
) equivalent to P interpreted as UTF-16
encoded Unicode code points (6.1.4), in which certain
code points are escaped as described below. S may or may not be identical to P; however, the
internal procedure that would result from evaluating S as a Pattern (Pattern[U] if
F contains "u"
) must behave identically to the
internal procedure given by the constructed object's [[RegExpMatcher]] internal slot. Multiple calls to this abstract
operation using the same values for P and F must produce identical results./
or any LineTerminator occurring in the pattern shall be escaped in S
as necessary to ensure that the String value formed by concatenating the Strings "/"
, S,
"/"
, and F can be parsed (in an appropriate lexical context) as a
RegularExpressionLiteral that behaves identically to the constructed regular expression. For example, if
P is "/"
, then S could be "\/"
or "\u002F"
, among other
possibilities, but not "/"
, because ///
followed by F would be parsed as a
SingleLineComment rather than a RegularExpressionLiteral. If P is the empty String, this
specification can be met by letting S be "(?:)"
.The value of the [[Prototype]] internal slot of the RegExp constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 2), the RegExp constructor has the following
properties:
The initial value of RegExp.prototype
is the intrinsic object %RegExpPrototype% (21.2.5).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
RegExp[@@species]
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE RegExp prototype methods normally use their this
object’s constructor
to create a derived object. However, a subclass constructor may over-ride that default behaviour by redefining its
@@species property.
The RegExp prototype object is the intrinsic object %RegExpPrototype%. The RegExp prototype object is an ordinary object. It is not a RegExp instance and does not have a [[RegExpMatcher]] internal slot or any of the other internal slots of RegExp instance objects.
The value of the [[Prototype]] internal slot of the RegExp prototype object is the intrinsic object %ObjectPrototype% (19.1.3).
NOTE The RegExp prototype object does not have a valueOf
property of its own;
however, it inherits the valueOf
property from the Object prototype object.
The initial value of RegExp.prototype.constructor
is the intrinsic object %RegExp%.
Performs a regular expression match of string against the regular expression and returns an Array object containing the results of the match, or null if string did not match.
The String ToString(string) is searched for an occurrence of the regular expression pattern as follows:
The abstract operation RegExpExec with arguments R and S performs the following steps:
"exec"
).NOTE If a callable exec
property is not found this algorithm falls back to
attempting to use the built-in RegExp matching algorithm. This provides compatible behaviour for code written for
prior editions where most built-in algorithms that use regular expressions did not perform a dynamic property lookup
of exec
.
The abstract operation RegExpBuiltinExec with arguments R and S performs the following steps:
"lastIndex"
))."global"
))."sticky"
))."u"
, let fullUnicode be true, else let fullUnicode be
false."lastIndex"
,
0, true)."lastIndex"
, 0, true)."lastIndex"
,
e, true)."length"
property is n + 1."index"
,
matchIndex)."input"
,
S)."0"
,
matchedSubstr).The abstract operation AdvanceStringIndex with arguments S, index, and unicode performs the following steps:
RegExp.prototype.flags
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
"global"
))."g"
as the last code unit of result."ignoreCase"
))."i"
as the last code unit of result."multiline"
))."m"
as the last code unit of result."unicode"
))."u"
as the last code unit of result."sticky"
))."y"
as the last code unit of result.RegExp.prototype.global
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
"g"
, return true.RegExp.prototype.ignoreCase
is an accessor property whose set accessor function is
undefined. Its get accessor function performs the following steps:
"i"
, return true.When the @@match
method is called with argument string, the following
steps are taken:
"global"
))."unicode"
))."lastIndex"
, 0,
true)."0"
))."lastIndex"
))."lastIndex"
,
nextIndex, true).The value of the name
property of this function is "[Symbol.match]"
.
NOTE The @@match property is used by the IsRegExp abstract operation to identify objects that have the basic behaviour of regular expressions. The absence of a @@match property or the existence of such a property whose value does not Boolean coerce to true indicates that the object is not intended to be used as a regular expression object.
RegExp.prototype.multiline
is an accessor property whose set accessor function is
undefined. Its get accessor function performs the following steps:
"m"
, return true.When the @@replace
method is called with arguments string and
replaceValue the following steps are taken:
"global"
))."unicode"
))."lastIndex"
, 0,
true)."0"
))."lastIndex"
))."lastIndex"
,
nextIndex, true)."length"
))."0"
))."index"
)).The value of the name
property of this function is "[Symbol.replace]"
.
When the @@search method is called with argument string, the following steps are taken:
"lastIndex"
)."lastIndex"
, 0,
true)."lastIndex"
,
previousLastIndex, true)."index"
).The value of the name
property of this function is "[Symbol.search]"
.
NOTE The lastIndex
and global
properties of this RegExp object are
ignored when performing the search. The lastIndex
property is left unchanged.
RegExp.prototype.source
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
NOTE 1 Returns an Array object into which substrings of the result of converting string to a String have been stored. The substrings are determined by searching from left to right for matches of the this value regular expression; these occurrences are not part of any substring in the returned array, but serve to divide up the String value.
The this value may be an empty regular expression or a regular expression that can match an
empty String. In this case, regular expression does not match the empty substring at the beginning or end of the input
String, nor does it match the empty substring at the end of the previous separator match. (For example, if the regular
expression matches the empty String, the String is split up into individual code unit elements; the length of the result
array equals the length of the String, and each substring contains one code unit.) Only the first match at a given index
of the this String is considered, even if backtracking could yield a non-empty-substring match at that index. (For
example, /a*?/[Symbol.split]("ab")
evaluates to the array ["a","b"]
, while
/a*/[Symbol.split]("ab")
evaluates to the array["","b"]
.)
If the string is (or converts to) the empty String, the result depends on whether the regular expression can match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty String.
If the regular expression that contains capturing parentheses, then each time separator is matched the results (including any undefined results) of the capturing parentheses are spliced into the output array. For example,
/<(\/)?([^<>]+)>/[Symbol.split]("A<B>bold</B>and<CODE>coded</CODE>")
evaluates to the array
["A",undefined,"B","bold","/","B","and",undefined,"CODE","coded","/","CODE",""]
If limit is not undefined, then the output array is truncated so that it contains no more than limit elements.
When the @@split
method is called, the following steps are taken:
"flags"
))."u"
, let unicodeMatching be true."y"
, let newFlags be flags."y"
."0"
,
S)."lastIndex"
,
q, true)."lastIndex"
))."length"
)).The length
property of the @@split
method is 2.
The value of the name
property of this function is "[Symbol.split]"
.
NOTE 2 The @@split
method ignores the value of the global
and
sticky
properties of this RegExp object.
RegExp.prototype.sticky
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
"y"
, return true.The following steps are taken:
"source"
))."flags"
))."/"
, pattern, and
"/"
, and flags.NOTE The returned String has the form of a RegularExpressionLiteral that evaluates to another RegExp object with the same behaviour as this object.
RegExp.prototype.unicode
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
"u"
, return true.RegExp instances are ordinary objects that inherit properties from the RegExp prototype object. RegExp instances have internal slots [[RegExpMatcher]], [[OriginalSource]], and [[OriginalFlags]]. The value of the [[RegExpMatcher]] internal slot is an implementation dependent representation of the Pattern of the RegExp object.
NOTE Prior to ECMAScript 2015, RegExp
instances were specified as having the own
data properties source
, global
, ignoreCase
, and multiline
. Those
properties are now specified as accessor properties of RegExp.prototype.
RegExp instances also have the following property:
The value of the lastIndex
property specifies the String index at which to start the next match. It is
coerced to an integer when used (see 21.2.5.2.2). This property shall have the
attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.
Array objects are exotic objects that give special treatment to a certain class of property names. See 9.4.2 for a definition of this special treatment.
The Array constructor is the %Array% intrinsic object and the initial value of the Array
property of the
global object. When called as a constructor it creates and initializes a new exotic Array object. When Array
is called as a function rather than as a constructor, it also creates and initializes a new Array object. Thus the
function call Array(…)
is equivalent to the object creation expression
new Array(…)
with the same arguments.
The Array
constructor is a single function whose behaviour is overloaded based upon the number and types
of its arguments.
The Array
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the exotic
Array
behaviour must include a super
call to the Array
constructor to initialize
subclass instances that are exotic Array objects. However, most of the Array.prototype
methods are generic
methods that are not dependent upon their this
value being an exotic Array object.
The length
property of the Array
constructor function is 1.
This description applies if and only if the Array constructor is called with no arguments.
"%ArrayPrototype%"
).This description applies if and only if the Array constructor is called with exactly one argument.
"%ArrayPrototype%"
)."0"
, len)."length"
, intLen,
true).This description applies if and only if the Array constructor is called with at least two arguments.
When the Array
function is called the following steps are taken:
"%ArrayPrototype%"
).length
property is
numberOfArgs.The value of the [[Prototype]] internal slot of the Array constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 1), the Array constructor has the following
properties:
When the from
method is called with argument items and optional arguments
mapfn and thisArg the following steps are taken:
"length"
,
k, true)."length"
))."length"
, len,
true).The length
property of the from
method is 1.
NOTE The from
function is an intentionally generic factory method; it does not
require that its this value be the Array constructor. Therefore it can be transferred to or inherited by any
other constructors that may be called with a single numeric argument.
The isArray
function takes one argument arg, and performs the following
steps:
When the of
method is called with any number of arguments, the following steps are
taken:
"length"
, len,
true).The length
property of the of
method is 0.
NOTE 1 The items argument is assumed to be a well-formed rest argument value.
NOTE 2 The of
function is an intentionally generic factory method; it does not
require that its this value be the Array constructor. Therefore it can be transferred to or inherited by other
constructors that may be called with a single numeric argument.
The value of Array.prototype
is %ArrayPrototype%, the intrinsic Array prototype object (22.1.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
Array[@@species]
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE Array prototype methods normally use their this
object’s constructor
to create a derived object. However, a subclass constructor may over-ride that default behaviour by redefining its
@@species property.
The Array prototype object is the intrinsic object %ArrayPrototype%. The Array prototype object is an Array exotic
objects and has the internal methods specified for such objects. It has a length
property whose initial value
is 0 and whose attributes are { [[Writable]]: true, [[Enumerable]]:
false, [[Configurable]]: false }.
The value of the [[Prototype]] internal slot of the Array prototype object is the intrinsic object %ObjectPrototype%.
NOTE The Array prototype object is specified to be an Array exotic object to ensure compatibility with ECMAScript code that was created prior to the ECMAScript 2015 specification.
When the concat
method is called with zero or more arguments, it returns an array containing the array
elements of the object followed by the array elements of each argument in order.
The following steps are taken:
"length"
))."length"
, n,
true).The length
property of the concat
method is 1.
NOTE 1 The explicit setting of the length
property in step 8 is necessary to
ensure that its value is correct in situations where the trailing elements of the result Array are not present.
NOTE 2 The concat
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
The abstract operation IsConcatSpreadable with argument O performs the following steps:
The initial value of Array.prototype.constructor
is the intrinsic object %Array%.
The copyWithin
method takes up to three arguments target, start
and end.
NOTE 1 The end argument is optional with the length of the this object as its default value. If target is negative, it is treated as length+target where length is the length of the array. If start is negative, it is treated as length+start. If end is negative, it is treated as length+end.
The following steps are taken:
"length"
)).The length
property of the copyWithin
method is 2.
NOTE 2 The copyWithin
function is intentionally generic; it does not require
that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
The following steps are taken:
"key+value"
).NOTE 1 callbackfn should be a function that accepts three arguments and returns a
value that is coercible to the Boolean value true or false. every
calls callbackfn
once for each element present in the array, in ascending order, until it finds one where callbackfn returns
false. If such an element is found, every
immediately returns false. Otherwise, if
callbackfn returned true for all elements, every
will return true.
callbackfn is called only for elements of the array which actually exist; it is not called for missing
elements of the array.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
every
does not directly mutate the object on which it is called but the object may be
mutated by the calls to callbackfn.
The range of elements processed by every
is set before the first call to
callbackfn. Elements which are appended to the array after the call to every
begins will not be
visited by callbackfn. If existing elements of the array are changed, their value as passed to
callbackfn will be the value at the time every
visits them; elements that are deleted after the
call to every
begins and before being visited are not visited. every
acts like the "for all"
quantifier in mathematics. In particular, for an empty array, it returns true.
When the every
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the every
method is 1.
NOTE 2 The every
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
The fill
method takes up to three arguments value, start and
end.
NOTE 1 The start and end arguments are optional with default values of 0 and the length of the this object. If start is negative, it is treated as length+start where length is the length of the array. If end is negative, it is treated as length+end.
The following steps are taken:
"length"
)).The length
property of the fill
method is 1.
NOTE 2 The fill
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 callbackfn should be a function that accepts three arguments and returns a
value that is coercible to the Boolean value true or false. filter
calls
callbackfn once for each element in the array, in ascending order, and constructs a new array of all the
values for which callbackfn returns true. callbackfn is called only for elements of the
array which actually exist; it is not called for missing elements of the array.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
filter
does not directly mutate the object on which it is called but the object may be
mutated by the calls to callbackfn.
The range of elements processed by filter
is set before the first call to
callbackfn. Elements which are appended to the array after the call to filter
begins will not be
visited by callbackfn. If existing elements of the array are changed their value as passed to
callbackfn will be the value at the time filter
visits them; elements that are deleted after the
call to filter
begins and before being visited are not visited.
When the filter
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the filter
method is 1.
NOTE 2 The filter
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
The find
method is called with one or two arguments, predicate and
thisArg.
NOTE 1 predicate should be a function that accepts three arguments and returns a
value that is coercible to a Boolean value. find
calls predicate once for each element of the
array, in ascending order, until it finds one where predicate returns true. If
such an element is found, find
immediately returns that element value. Otherwise, find
returns
undefined.
If a thisArg parameter is provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.
predicate is called with three arguments: the value of the element, the index of the element, and the object being traversed.
find
does not directly mutate the object on which it is called but the object may be
mutated by the calls to predicate.
The range of elements processed by find
is set before the first call to
callbackfn. Elements that are appended to the array after the call to find
begins will not be
visited by callbackfn. If existing elements of the array are changed, their value as passed to
predicate will be the value at the time that find
visits them.
When the find
method is called, the following steps are taken:
"length"
)).The length
property of the find
method is 1.
NOTE 2 The find
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 predicate should be a function that accepts three arguments and returns a
value that is coercible to the Boolean value true or false. findIndex
calls
predicate once for each element of the array, in ascending order, until it finds one where
predicate returns true. If such an element is found, findIndex
immediately returns the
index of that element value. Otherwise, findIndex
returns -1.
If a thisArg parameter is provided, it will be used as the this value for each invocation of predicate. If it is not provided, undefined is used instead.
predicate is called with three arguments: the value of the element, the index of the element, and the object being traversed.
findIndex
does not directly mutate the object on which it is called but the object may be
mutated by the calls to predicate.
The range of elements processed by findIndex
is set before the first call to
callbackfn. Elements that are appended to the array after the call to findIndex
begins will not be
visited by callbackfn. If existing elements of the array are changed, their value as passed to
predicate will be the value at the time that findIndex
visits them.
When the findIndex
method is called with one or two arguments, the following steps
are taken:
"length"
)).The length
property of the findIndex
method is 1.
NOTE 2 The findIndex
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 callbackfn should be a function that accepts three arguments.
forEach
calls callbackfn once for each element present in the array, in ascending order.
callbackfn is called only for elements of the array which actually exist; it is not called for missing
elements of the array.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
forEach
does not directly mutate the object on which it is called but the object may be mutated by the
calls to callbackfn.
When the forEach
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the forEach
method is 1.
NOTE 2 The forEach
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 indexOf
compares searchElement to the elements of the array,
in ascending order, using the Strict Equality Comparison algorithm (7.2.13), and if found at one or more indices, returns the smallest such
index; otherwise, −1 is returned.
The optional second argument fromIndex defaults to 0 (i.e. the whole array is searched). If it is greater than or equal to the length of the array, −1 is returned, i.e. the array will not be searched. If it is negative, it is used as the offset from the end of the array to compute fromIndex. If the computed index is less than 0, the whole array will be searched.
When the indexOf
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the indexOf
method is 1.
NOTE 2 The indexOf
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 The elements of the array are converted to Strings, and these Strings are then concatenated, separated by occurrences of the separator. If no separator is provided, a single comma is used as the separator.
The join
method takes one argument, separator, and performs the following
steps:
"length"
)).","
."0"
).1
.The length
property of the join
method is 1.
NOTE 2 The join
function is intentionally generic; it does not require that its
this value be an Array object. Therefore, it can be transferred to other kinds of objects for use as a
method.
The following steps are taken:
"key"
).NOTE 1 lastIndexOf
compares searchElement to the elements of the
array in descending order using the Strict Equality Comparison algorithm (7.2.13), and if found at one or more indices, returns the largest such index;
otherwise, −1 is returned.
The optional second argument fromIndex defaults to the array's length minus one (i.e. the whole array is searched). If it is greater than or equal to the length of the array, the whole array will be searched. If it is negative, it is used as the offset from the end of the array to compute fromIndex. If the computed index is less than 0, −1 is returned.
When the lastIndexOf
method is called with one or two arguments, the following steps
are taken:
"length"
)).The length
property of the lastIndexOf
method is 1.
NOTE 2 The lastIndexOf
function is intentionally generic; it does not require
that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 callbackfn should be a function that accepts three arguments.
map
calls callbackfn once for each element in the array, in ascending order, and constructs a
new Array from the results. callbackfn is called only for elements of the array which actually exist; it is
not called for missing elements of the array.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
map
does not directly mutate the object on which it is called but the object may be mutated by the calls
to callbackfn.
The range of elements processed by map
is set before the first call to callbackfn. Elements
which are appended to the array after the call to map
begins will not be visited by callbackfn.
If existing elements of the array are changed, their value as passed to callbackfn will be the value at the
time map
visits them; elements that are deleted after the call to map
begins and before being
visited are not visited.
When the map
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the map
method is 1.
NOTE 2 The map
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 The last element of the array is removed from the array and returned.
When the pop
method is called the following steps are taken:
"length"
))."length"
, 0,
true)."length"
, newLen,
true).NOTE 2 The pop
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 The arguments are appended to the end of the array, in the order in which they appear. The new length of the array is returned as the result of the call.
When the push
method is called with zero or more arguments the following steps are
taken:
"length"
))."length"
, len,
true).The length
property of the push
method is 1.
NOTE 2 The push
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 callbackfn should be a function that takes four arguments.
reduce
calls the callback, as a function, once for each element present in the array, in ascending
order.
callbackfn is called with four arguments: the previousValue (value from the previous call to
callbackfn), the currentValue (value of the current element), the currentIndex, and the object
being traversed. The first time that callback is called, the previousValue and currentValue can be one of
two values. If an initialValue was provided in the call to reduce
, then previousValue
will be equal to initialValue and currentValue will be equal to the first value in the array. If no
initialValue was provided, then previousValue will be equal to the first value in the array and
currentValue will be equal to the second. It is a TypeError if the array contains no elements and
initialValue is not provided.
reduce
does not directly mutate the object on which it is called but the object may be mutated by the
calls to callbackfn.
The range of elements processed by reduce
is set before the first call to callbackfn.
Elements that are appended to the array after the call to reduce
begins will not be visited by
callbackfn. If existing elements of the array are changed, their value as passed to callbackfn
will be the value at the time reduce
visits them; elements that are deleted after the call to
reduce
begins and before being visited are not visited.
When the reduce
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the reduce
method is 1.
NOTE 2 The reduce
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 callbackfn should be a function that takes four arguments.
reduceRight
calls the callback, as a function, once for each element present in the array, in descending
order.
callbackfn is called with four arguments: the previousValue (value from the previous call to
callbackfn), the currentValue (value of the current element), the currentIndex, and the
object being traversed. The first time the function is called, the previousValue and currentValue
can be one of two values. If an initialValue was provided in the call to reduceRight
, then
previousValue will be equal to initialValue and currentValue will be equal to the last
value in the array. If no initialValue was provided, then previousValue will be equal to the last
value in the array and currentValue will be equal to the second-to-last value. It is a TypeError if
the array contains no elements and initialValue is not provided.
reduceRight
does not directly mutate the object on which it is called but the object may be mutated by
the calls to callbackfn.
The range of elements processed by reduceRight
is set before the first call to callbackfn.
Elements that are appended to the array after the call to reduceRight
begins will not be visited by
callbackfn. If existing elements of the array are changed by callbackfn, their value as passed to
callbackfn will be the value at the time reduceRight
visits them; elements that are deleted
after the call to reduceRight
begins and before being visited are not visited.
When the reduceRight
method is called with one or two arguments, the following steps
are taken:
"length"
)).The length
property of the reduceRight
method is 1.
NOTE 2 The reduceRight
function is intentionally generic; it does not require
that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 The elements of the array are rearranged so as to reverse their order. The object is returned as the result of the call.
When the reverse
method is called the following steps are taken:
"length"
)).NOTE 2 The reverse
function is intentionally generic; it does not require that
its this value be an Array object. Therefore, it can be transferred to other kinds of objects for use as a
method.
NOTE 1 The first element of the array is removed from the array and returned.
When the shift
method is called the following steps are taken:
"length"
))."length"
, 0,
true)."0"
)."length"
, len–1,
true).NOTE 2 The shift
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 The slice
method takes two arguments, start and
end, and returns an array containing the elements of the array from element start up to, but not
including, element end (or through the end of the array if end is undefined). If
start is negative, it is treated as length+start where length is the length of the array. If end is
negative, it is treated as length+end where
length is the length of the array.
The following steps are taken:
"length"
))."length"
, n,
true).The length
property of the slice
method is 2.
NOTE 2 The explicit setting of the length
property of the result Array in step
16 is necessary to ensure that its value is correct in situations where the trailing elements of the result Array are
not present.
NOTE 3 The slice
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
NOTE 1 callbackfn should be a function that accepts three arguments and returns a
value that is coercible to the Boolean value true or false. some
calls callbackfn
once for each element present in the array, in ascending order, until it finds one where callbackfn returns
true. If such an element is found, some
immediately returns true. Otherwise,
some
returns false. callbackfn is called only for elements of the array which actually
exist; it is not called for missing elements of the array.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
some
does not directly mutate the object on which it is called but the object may be mutated by the
calls to callbackfn.
The range of elements processed by some
is set before the first call to callbackfn. Elements
that are appended to the array after the call to some
begins will not be visited by callbackfn.
If existing elements of the array are changed, their value as passed to callbackfn will be the value at the
time that some
visits them; elements that are deleted after the call to some
begins and before
being visited are not visited. some
acts like the "exists" quantifier in mathematics. In particular, for an
empty array, it returns false.
When the some
method is called with one or two arguments, the following steps are
taken:
"length"
)).The length
property of the some
method is 1.
NOTE 2 The some
function is intentionally generic; it does not require that its
this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.
The elements of this array are sorted. The sort is not necessarily stable (that is, elements that compare equal do not necessarily remain in their original order). If comparefn is not undefined, it should be a function that accepts two arguments x and y and returns a negative value if x < y, zero if x = y, or a positive value if x > y.
Upon entry, the following steps are performed to initialize evaluation of the sort
function:
"length"
)).Within this specification of the sort
method, an object, obj, is said
to be sparse if the following algorithm returns true:
The sort order is the ordering, after completion of this function, of the integer indexed property values of
obj whose integer indexes are less than len. The result of the sort
function is then
determined as follows:
If comparefn is not undefined and is not a consistent comparison function for the elements of this array (see below), the sort order is implementation-defined. The sort order is also implementation-defined if comparefn is undefined and SortCompare (22.1.3.24.1) does not act as a consistent comparison function.
Let proto be obj.[[GetPrototypeOf]](). If proto is not null and there exists an integer j such that all of the conditions below are satisfied then the sort order is implementation-defined:
The sort order is also implementation defined if obj is sparse and any of the following conditions are true:
IsExtensible(obj) is false.
Any integer index property of obj whose name is a nonnegative integer less than len is a data property whose [[Configurable]] attribute is false.
The sort order is also implementation defined if any of the following conditions are true:
If obj is an exotic object (including Proxy exotic objects) whose behaviour for [[Get]], [[Set]], [[Delete]], and [[GetOwnProperty]] is not the ordinary object implementation of these internal methods.
If any index index property of obj whose name is a nonnegative integer less than len is an accessor property or is a data property whose [[Writable]] attribute is false.
If comparefn is undefined and the application of ToString to any value passed as an argument to SortCompare modifies obj or any object on obj’s prototype chain.
If comparefn is undefined and all applications of ToString, to any specific value passed as an argument to SortCompare, do not produce the same result.
The following steps are taken:
The property key argument for each call to [[Get]], [[Set]], HasOwnProperty, or DeletePropertyOrThrow is the string representation of a nonnegative integer less than len.
The arguments for calls to SortCompare are values returned by a previous call to the [[Get]] internal method, unless the properties accessed by those previous calls did not exist according to HasOwnProperty. If both perspective arguments to SortCompare correspond to non-existent properties, use +0 instead of calling SortCompare. If only the first perspective argument is non-existent use +1. If only the second perspective argument is non-existent use −1.
If obj is not sparse then DeletePropertyOrThrow must not be called.
If any [[Set]] call returns false a TypeError exception is thrown.
If an abrupt completion is returned from any of these operations, it is immediately returned as the value of this function.
Unless the sort order is specified above to be implementation-defined, the returned object must have the following two characteristics:
There must be some mathematical permutation π of the nonnegative integers less than len, such that for every nonnegative integer j less than len, if property old[j] existed, then new[π(j)] is exactly the same value as old[j]. But if property old[j] did not exist, then new[π(j)] does not exist.
Then for all nonnegative integers j and k, each less than len, if SortCompare(old[j], old[k]) < 0 (see SortCompare below), then new[π(j)] < new[π(k)].
Here the notation old[j] is used to refer to the hypothetical result of calling the [[Get]] internal method of obj with argument j before this function is executed, and the notation new[j] to refer to the hypothetical result of calling the [[Get]] internal method of obj with argument j after this function has been executed.
A function comparefn is a consistent comparison function for a set of values S if all of the requirements below are met for all values a, b, and c (possibly the same value) in the set S: The notation a <CF b means comparefn(a,b) < 0; a =CF b means comparefn(a,b) = 0 (of either sign); and a >CF b means comparefn(a,b) > 0.
Calling comparefn(a,b) always returns the same value v when given a specific pair of values a and b as its two arguments. Furthermore, Type(v) is Number, and v is not NaN. Note that this implies that exactly one of a <CF b, a =CF b, and a >CF b will be true for a given pair of a and b.
Calling comparefn(a,b) does not modify obj or any object on obj’s prototype chain.
a =CF a (reflexivity)
If a =CF b, then b =CF a (symmetry)
If a =CF b and b =CF c, then a =CF c (transitivity of =CF)
If a <CF b and b <CF c, then a <CF c (transitivity of <CF)
If a >CF b and b >CF c, then a >CF c (transitivity of >CF)
NOTE 1 The above conditions are necessary and sufficient to ensure that comparefn divides the set S into equivalence classes and that these equivalence classes are totally ordered.
NOTE 2 The sort
function is intentionally generic; it does not require that
its this value be an Array object. Therefore, it can be transferred to other kinds of objects for use as a
method.
The SortCompare abstract operation is called with two arguments x and y.
It also has access to the comparefn argument passed to the current invocation of the sort
method. The following steps are taken:
NOTE 1 Because non-existent property values always compare greater than undefined property values, and undefined always compares greater than any other value, undefined property values always sort to the end of the result, followed by non-existent property values.
NOTE 2 Method calls performed by the ToString abstract operations in steps 5 and 7 have the potential to cause SortCompare to not behave as a consistent comparison function.
NOTE 1 When the splice
method is called with two or more arguments
start, deleteCount and zero or more items, the deleteCount elements of the
array starting at integer index start are replaced by the arguments items. An Array object
containing the deleted elements (if any) is returned.
The following steps are taken:
"length"
))."length"
,
actualDeleteCount, true)."length"
, len –
actualDeleteCount + itemCount, true).The length
property of the splice
method is 2.
NOTE 2 The explicit setting of the length
property of the result Array in step
24 is necessary to ensure that its value is correct in situations where its trailing elements are not present.
NOTE 3 The splice
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement the
Array.prototype.toLocaleString
method as specified in the ECMA-402 specification. If an ECMAScript
implementation does not include the ECMA-402 API the following specification of the toLocaleString
method is
used.
NOTE 1 The first edition of ECMA-402 did not include a replacement specification for the
Array.prototype.toLocaleString
method.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
The following steps are taken:
"length"
))."0"
)."toLocaleString"
)).1
."toLocaleString"
)).NOTE 2 The elements of the array are converted to Strings using their
toLocaleString
methods, and these Strings are then concatenated, separated by occurrences of a separator
String that has been derived in an implementation-defined locale-specific way. The result of calling this function is
intended to be analogous to the result of toString
, except that the result of this function is intended to
be locale-specific.
NOTE 3 The toLocaleString
function is intentionally generic; it does not require
that its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
When the toString
method is called, the following steps are taken:
"join"
).NOTE The toString
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
NOTE 1 The arguments are prepended to the start of the array, such that their order within the array is the same as the order in which they appear in the argument list.
When the unshift
method is called with zero or more arguments item1,
item2, etc., the following steps are taken:
"length"
))."length"
,
len+argCount, true).The length
property of the unshift
method is 1.
NOTE 2 The unshift
function is intentionally generic; it does not require that
its this value be an Array object. Therefore it can be transferred to other kinds of objects for use as a
method.
The following steps are taken:
"value"
).This function is the %ArrayProto_values% intrinsic object.
The initial value of the @@iterator property is the same function object as the initial value of the Array.prototype.values property.
The initial value of the @@unscopables data property is an object created by the following steps:
"copyWithin"
,
true)."entries"
,
true)."fill"
,
true)."find"
,
true)."findIndex"
,
true)."keys"
,
true)."values"
,
true).This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
NOTE The own property names of this object are property names that were not included as
standard properties of Array.prototype
prior to the ECMAScript 2015 specification. These names are ignored
for with
statement binding purposes in order to preserve the behaviour of existing code that might use one
of these names as a binding in an outer scope that is shadowed by a with
statement whose binding object is
an Array object.
Array instances are Array exotic objects and have the internal methods specified for such objects. Array instances inherit properties from the Array prototype object.
Array instances have a length
property, and a set of enumerable properties with array index names.
The length
property of an Array instance is a data property whose value is always numerically greater than
the name of every configurable own property whose name is an array index.
The length
property initially has the attributes {
[[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE Reducing the value of the length
property has the side-effect of deleting
own array elements whose array index is between the old and new length values. However, non-configurable properties can
not be deleted. Attempting to set the length property of an Array object to a value that is numerically less than or
equal to the largest numeric own property name of an existing non-configurable array indexed property of the array will
result in the length being set to a numeric value that is one greater than that non-configurable numeric own property
name. See 9.4.2.1.
An Array Iterator is an object, that represents a specific iteration over some specific Array instance object. There is not a named constructor for Array Iterator objects. Instead, Array iterator objects are created by calling certain methods of Array instance objects.
Several methods of Array objects return Iterator objects. The abstract operation CreateArrayIterator with arguments array and kind is used to create such iterator objects. It performs the following steps:
All Array Iterator Objects inherit properties from the %ArrayIteratorPrototype% intrinsic object. The %ArrayIteratorPrototype% object is an ordinary object and its [[Prototype]] internal slot is the %IteratorPrototype% intrinsic object (25.1.2). In addition, %ArrayIteratorPrototype% has the following properties:
"length"
)).key
", return CreateIterResultObject(index, false).value
", let result be elementValue.key+value
".The initial value of the @@toStringTag property is the String value "Array Iterator"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Array Iterator instances are ordinary objects that inherit properties from the %ArrayIteratorPrototype% intrinsic object. Array Iterator instances are initially created with the internal slots listed in Table 48.
Internal Slot | Description |
---|---|
[[IteratedObject]] | The object whose array elements are being iterated. |
[[ArrayIteratorNextIndex]] | The integer index of the next integer index to be examined by this iteration. |
[[ArrayIterationKind]] | A String value that identifies what is returned for each element of the iteration. The possible values are: "key" , "value" , "key+value" . |
TypedArray objects present an array-like view of an underlying binary data buffer (24.1). Each element of a TypedArray instance has the same underlying binary scalar data type. There is a distinct TypedArray constructor, listed in Table 49, for each of the nine supported element types. Each constructor in Table 49 has a corresponding distinct prototype object.
Constructor Name and Intrinsic | Element Type | Element Size | Conversion Operation | Description | Equivalent C Type |
---|---|---|---|---|---|
Int8Array %Int8Array% |
Int8 | 1 | ToInt8 | 8-bit 2’s complement signed integer | signed char |
Uint8Array %Uint8Array% |
Uint8 | 1 | ToUint8 | 8-bit unsigned integer | unsigned char |
Uint8ClampedArray %Uint8ClampedArray% |
Uint8C | 1 | ToUint8Clamp | 8-bit unsigned integer (clamped conversion) | unsigned char |
Int16Array %Int16Array% |
Int16 | 2 | ToInt16 | 16-bit 2’s complement signed integer | short |
Uint16Array %Uint16Array% |
Uint16 | 2 | ToUint16 | 16-bit unsigned integer | unsigned short |
Int32Array %Int32Array% |
Int32 | 4 | ToInt32 | 32-bit 2’s complement signed integer | int |
Uint32Array %Uint32Array% |
Uint32 | 4 | ToUint32 | 32-bit unsigned integer | unsigned int |
Float32Array %Float32Array% |
Float32 | 4 | 32-bit IEEE floating point | float | |
Float64Array %Float64Array% |
Float64 | 8 | 64-bit IEEE floating point | double |
In the definitions below, references to TypedArray should be replaced with the appropriate constructor name from the above table. The phrase “the element size in bytes” refers to the value in the Element Size column of the table in the row corresponding to the constructor. The phrase “element Type” refers to the value in the Element Type column for that row.
The %TypedArray% intrinsic object is a constructor function object that all of the TypedArray constructor object inherit from. %TypedArray% and its corresponding prototype object provide common properties that are inherited by all TypedArray constructors and their instances. The %TypedArray% intrinsic does not have a global name or appear as a property of the global object.
The %TypedArray% intrinsic function object is designed to act as the superclass of the various TypedArray
constructors. Those constructors use %TypedArray% to initialize their instances by invoking %TypedArray% as if by making a
super
call. The %TypedArray% intrinsic function is not designed to be directly called in any other way. If
%TypedArray% is directly called or called as part of a new
expression an exception is thrown.
The %TypedArray% intrinsic constructor function is a single function whose behaviour is overloaded based upon the
number and types of its arguments. The actual behaviour of a super
call of %TypedArray% depends upon the
number and kind of arguments that are passed to it.
This description applies only if the %TypedArray% function is called with no arguments.
This description applies only if the %TypedArray% function is called with at least one argument and the Type of the first argument is not Object.
%TypedArray% called with argument length performs the following steps:
The abstract operation AllocateTypedArray with argument newTarget and optional argument length is used to validate and create an instance of a TypedArray constructor. If the length argument is passed an ArrayBuffer of that length is also allocated and associated with the new TypedArray instance. AllocateTypedArray provides common semantics that is used by all of the %TypeArray% overloads and other methods. AllocateTypedArray performs the following steps:
new
operator. It can only be successfully invoked by a SuperCall."%TypedArrayPrototype%"
).This description applies only if the %TypedArray% function is called with at least one argument and the Type of the first argument is Object and that object has a [[TypedArrayName]] internal slot.
%TypedArray% called with argument typedArray performs the following steps:
This description applies only if the %TypedArray% function is called with at least one argument and the Type of the first argument is Object and that object does not have either a [[TypedArrayName]] or an [[ArrayBufferData]] internal slot.
%TypedArray% called with argument object performs the following steps:
This description applies only if the %TypedArray% function is called with at least one argument and the Type of the first argument is Object and that object has an [[ArrayBufferData]] internal slot.
%TypedArray% called with arguments buffer, byteOffset, and length performs the following steps:
The value of the [[Prototype]] internal slot of %TypedArray% is the intrinsic object %FunctionPrototype% (19.2.3).
Besides a length
property whose value is 3 and a name
property whose value is
"TypedArray"
, %TypedArray% has the following properties:
When the from
method is called with argument source, and optional
arguments mapfn and thisArg, the following steps are taken:
The length
property of the from
method is 1.
When the TypedArrayFrom abstract operation is called with arguments constructor, items, mapfn, and thisArg, the following steps are taken:
"length"
)).When the of
method is called with any number of arguments, the following steps are
taken:
The length
property of the of
method is 0.
NOTE The items argument is assumed to be a well-formed rest argument value.
The initial value of %TypedArray%.prototype is the %TypedArrayPrototype% intrinsic object (22.2.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
%TypedArray%[@@species] is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE %TypedArrayPrototype% methods normally use their this
object’s
constructor to create a derived object. However, a subclass constructor may over-ride that default behaviour by
redefining its @@species property.
The value of the [[Prototype]] internal slot of the %TypedArrayPrototype% object is the intrinsic object %ObjectPrototype% (19.1.3). The %TypedArrayPrototype% object is an ordinary object. It does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.
%TypedArray%.prototype.buffer
is an accessor property whose set accessor function is
undefined. Its get accessor function performs the following steps:
%TypedArray%.prototype.byteLength
is an accessor property whose set accessor function
is undefined. Its get accessor function performs the following steps:
%TypedArray%.prototype.byteOffset
is an accessor property whose set accessor function
is undefined. Its get accessor function performs the following steps:
The initial value of %TypedArray%.prototype.constructor is the %TypedArray% intrinsic object.
%TypedArray%.prototype.copyWithin
is a distinct function that implements the same algorithm as Array.prototype.copyWithin
as defined in 22.1.3.3 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
and the actual copying of values in step 17 must be performed in a manner that preserves the
bit-level encoding of the source data
The implementation of the algorithm may be optimized with the knowledge that the this value is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the copyWithin
method is 2.
When called with argument O the following steps are taken:
The following steps are taken:
"key+value"
).%TypedArray%.prototype.every
is a distinct function that implements the same algorithm as Array.prototype.every
as defined in 22.1.3.5 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to callbackfn may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the every
method is 1.
%TypedArray%.prototype.fill
is a distinct function that implements the same algorithm as Array.prototype.fill
as defined in 22.1.3.6 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the fill
method is 1.
The interpretation and use of the arguments of %TypedArray%.prototype.filter
are the same as for Array.prototype.filter
as defined in 22.1.3.7.
When the filter
method is called with one or two arguments, the following steps are
taken:
This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
The length
property of the filter
method is 1.
%TypedArray%.prototype.find
is a distinct function that implements the same algorithm as Array.prototype.find
as defined in 22.1.3.8 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to predicate may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the find
method is 1.
%TypedArray%.prototype.findIndex
is a distinct function that implements the same algorithm as Array.prototype.findIndex
as defined in 22.1.3.9 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to predicate may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the findIndex
method is 1.
%TypedArray%.prototype.forEach
is a distinct function that implements the same algorithm as Array.prototype.forEach
as defined in 22.1.3.10 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to callbackfn may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the forEach
method is 1.
%TypedArray%.prototype.indexOf
is a distinct function that implements the same algorithm as Array.prototype.indexOf
as defined in 22.1.3.11 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the indexOf
method is 1.
%TypedArray%.prototype.join
is a distinct function that implements the same algorithm as Array.prototype.join
as defined in 22.1.3.12 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The following steps are taken:
"key"
).%TypedArray%.prototype.lastIndexOf
is a distinct function that implements the same algorithm as Array.prototype.lastIndexOf
as defined in 22.1.3.14 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the lastIndexOf
method is 1.
%TypedArray%.prototype.length
is an accessor property whose set accessor function is
undefined. Its get accessor function performs the following steps:
This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
The interpretation and use of the arguments of %TypedArray%.prototype.map
are the same as for Array.prototype.map
as defined in 22.1.3.15.
When the map
method is called with one or two arguments, the following steps are
taken:
This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
The length
property of the map
method is 1.
%TypedArray%.prototype.reduce
is a distinct function that implements the same algorithm as Array.prototype.reduce
as defined in 22.1.3.18 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to callbackfn may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the reduce
method is 1.
%TypedArray%.prototype.reduceRight
is a distinct function that implements the same algorithm as Array.prototype.reduceRight
as defined in 22.1.3.19 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to callbackfn may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the reduceRight
method is 1.
%TypedArray%.prototype.reverse
is a distinct function that implements the same algorithm as Array.prototype.reverse
as defined in 22.1.3.20 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
%TypedArray%.prototype.set
is a single function whose behaviour is overloaded based upon the type of its
first argument.
This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
The length
property of the set
method is 1.
Sets multiple values in this TypedArray, reading the values from the object array. The optional offset value indicates the first element index in this TypedArray where values are written. If omitted, it is assumed to be 0.
"length"
)).Sets multiple values in this TypedArray, reading the values from the typedArray argument object. The optional offset value indicates the first element index in this TypedArray where values are written. If omitted, it is assumed to be 0.
"Uint8"
)."Uint8"
, value).The interpretation and use of the arguments of %TypedArray%.prototype.slice
are the
same as for Array.prototype.slice
as defined in 22.1.3.22. The following steps are taken:
"Uint8"
)."Uint8"
, value).This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
The length
property of the slice
method is 2.
%TypedArray%.prototype.some
is a distinct function that implements the same algorithm as Array.prototype.some
as defined in 22.1.3.23 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm and must take into account the
possibility that calls to callbackfn may cause the this value to become detached.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
The length
property of the some
method is 1.
%TypedArray%.prototype.sort
is a distinct function that, except as described below, implements the same
requirements as those of Array.prototype.sort
as defined in 22.1.3.24. The implementation of the %TypedArray%.prototype.sort
specification may be optimized with the knowledge that the this value is an object that has a fixed length and
whose integer indexed properties are not sparse. The only internal methods of the this object that the algorithm
may call are [[Get]] and [[Set]].
This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
Upon entry, the following steps are performed to initialize evaluation of the sort
function. These steps are used instead of the entry steps in 22.1.3.24:
The implementation defined sort order condition for exotic objects is not applied by
%TypedArray%.prototype.sort
.
The following version of SortCompare is used by
%TypedArray%.prototype.sort
. It performs a numeric comparison rather than the string comparison used in 22.1.3.24. SortCompare has access to the
comparefn and buffer values of the current invocation of the sort
method.
When the TypedArray SortCompare abstract operation is called with two arguments x and y, the following steps are taken:
NOTE Because NaN always compares greater than any other value, NaN property values always sort to the end of the result when comparefn is not provided.
Returns a new TypedArray object whose element type is the same as this TypedArray and whose ArrayBuffer is the same as the ArrayBuffer of this TypedArray, referencing the elements at begin, inclusive, up to end, exclusive. If either begin or end is negative, it refers to an index from the end of the array, as opposed to from the beginning.
This function is not generic. The this value must be an object with a [[TypedArrayName]] internal slot.
The length
property of the subarray
method is 2.
%TypedArray%.prototype.toLocaleString
is a distinct function that implements the same algorithm as
Array.prototype.
toLocaleString
as defined in 22.1.3.26 except that the this object’s [[ArrayLength]] internal slot is accessed in place of performing a [[Get]] of
"length"
. The implementation of the algorithm may be optimized with the knowledge that the this value
is an object that has a fixed length and whose integer indexed properties are not sparse. However, such optimization must
not introduce any observable changes in the specified behaviour of the algorithm.
This function is not generic. ValidateTypedArray is applied to the this value prior to evaluating the algorithm. If its result is an abrupt completion that exception is thrown instead of evaluating the algorithm.
NOTE If the ECMAScript implementation includes the ECMA-402 Internationalization API this
function is based upon the algorithm for Array.prototype.toLocaleString
that is in the ECMA-402
specification.
The initial value of the %TypedArray%.prototype.toString
data property is the same built-in function
object as the Array.prototype.toString
method defined in 22.1.3.27.
The following steps are taken:
"value"
).The initial value of the @@iterator property is the same function object as the initial value of the
%TypedArray%.prototype.values
property.
%TypedArray%.prototype[@@toStringTag]
is an accessor property whose set accessor
function is undefined. Its get accessor function performs the following steps:
This property has the attributes { [[Enumerable]]: false, [[Configurable]]: true }.
The initial value of the name
property of this function is "get [Symbol.toStringTag]"
.
Each of the TypedArray constructor objects is an intrinsic object that has the structure described below, differing only in the name used as the constructor name instead of TypedArray, in Table 49.
The TypedArray constructors are not intended to be called as a function and will throw an exception when called in that manner.
The TypedArray constructors are designed to be subclassable. They may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
TypedArray behaviour must include a super
call to the TypedArray constructor to create and
initialize the subclass instance with the internal state necessary to support the %TypedArray%.prototype
built-in methods.
A TypedArray constructor with a list of arguments argumentsList performs the following steps:
The value of the [[Prototype]] internal slot of each TypedArray constructor is the %TypedArray% intrinsic object (22.2.1).
Each TypedArray constructor has a [[TypedArrayConstructorName]] internal slot property whose value is the String value of the constructor name specified for it in Table 49.
Each TypedArray constructor has a name
property whose value is the String value of the constructor
name specified for it in Table 49.
Besides a length
property (whose value is 3), each TypedArray constructor has the following
properties:
The value of TypedArray.BYTES_PER_ELEMENT is the Number value of the Element Size value specified in Table 49 for TypedArray.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of TypedArray.prototype is the corresponding TypedArray prototype intrinsic object (22.2.6).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The value of the [[Prototype]] internal slot of a TypedArray prototype object is the intrinsic object %TypedArrayPrototype% (22.2.3). A TypedArray prototype object is an ordinary object. It does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.
The value of TypedArray.prototype.BYTES_PER_ELEMENT
is the Number value of the Element Size value
specified in Table 49 for TypedArray.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The initial value of a TypedArray.prototype.constructor
is the corresponding %TypedArray%
intrinsic object.
TypedArray instances are Integer Indexed exotic objects. Each TypedArray instance inherits properties from the corresponding TypedArray prototype object. Each TypedArray instance has the following internal slots: [[TypedArrayName]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]], and [[ArrayLength]].
Map objects are collections of key/value pairs where both the keys and values may be arbitrary ECMAScript language values. A distinct key value may only occur in one key/value pair within the Map’s collection. Distinct key values are discriminated using the SameValueZero comparison algorithm.
Map object must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structures used in this Map objects specification is only intended to describe the required observable semantics of Map objects. It is not intended to be a viable implementation model.
The Map constructor is the %Map% intrinsic object and the initial value of the Map
property of the global
object. When called as a constructor it creates and initializes a new Map object. Map
is not intended to be
called as a function and will throw an exception when called in that manner.
The Map
constructor is designed to be subclassable. It may be used as the value in an extends
clause of a class definition. Subclass constructors that intend to inherit the specified Map
behaviour must
include a super
call to the Map
constructor to create and initialize the subclass instance with
the internal state necessary to support the Map.prototype
built-in methods.
When the Map
function is called with optional argument the following steps are
taken:
"%MapPrototype%"
, «[[MapData]]» )."set"
)."0"
)."1"
).NOTE If the parameter iterable is present, it is expected to be an object that implements an @@iterator method that returns an iterator object that produces a two element array-like object whose first element is a value that will be used as a Map key and whose second element is the value to associate with that key.
The value of the [[Prototype]] internal slot of the Map constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 0), the Map constructor has the following
properties:
The initial value of Map.prototype
is the intrinsic object %MapPrototype% (23.1.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
Map[@@species]
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE Methods that create derived collection objects should call @@species to determine the constructor to use to create the derived objects. Subclass constructor may over-ride @@species to change the default constructor assignment.
The Map prototype object is the intrinsic object %MapPrototype%. The value of the [[Prototype]] internal slot of the Map prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The Map prototype object is an ordinary object. It does not have a [[MapData]] internal slot.
The following steps are taken:
The initial value of Map.prototype.constructor
is the intrinsic object %Map%.
The following steps are taken:
NOTE The value empty is used as a specification device to indicate that an entry has been deleted. Actual implementations may take other actions such as physically removing the entry from internal data structures.
The following steps are taken:
"key+value"
).When the forEach
method is called with one or two arguments, the following steps are
taken:
The length
property of the forEach
method is 1.
NOTE callbackfn should be a function that accepts three arguments.
forEach
calls callbackfn once for each key/value pair present in the map object, in key
insertion order. callbackfn is called only for keys of the map which actually exist; it is not called for
keys that have been deleted from the map.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the value of the item, the key of the item, and the Map object being traversed.
forEach
does not directly mutate the object on which it is called but the object may be mutated by the
calls to callbackfn. Each entry of a map’s [[MapData]] is only visited once. New keys added after the
call to forEach
begins are visited. A key will be revisited if it is deleted after it has been visited and
then re-added before the forEach
call completes. Keys that are deleted after the call to
forEach
begins and before being visited are not visited unless the key is added again before the
forEach
call completes.
The following steps are taken:
The following steps are taken:
The following steps are taken:
"key"
).The following steps are taken:
Map.prototype.size is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The following steps are taken:
"value"
).The initial value of the @@iterator property is the same function object as the initial value of the entries property.
The initial value of the @@toStringTag property is the String value "Map"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Map instances are ordinary objects that inherit properties from the Map prototype. Map instances also have a [[MapData]] internal slot.
A Map Iterator is an object, that represents a specific iteration over some specific Map instance object. There is not a named constructor for Map Iterator objects. Instead, map iterator objects are created by calling certain methods of Map instance objects.
Several methods of Map objects return Iterator objects. The abstract operation CreateMapIterator with arguments map and kind is used to create such iterator objects. It performs the following steps:
All Map Iterator Objects inherit properties from the %MapIteratorPrototype% intrinsic object. The %MapIteratorPrototype% intrinsic object is an ordinary object and its [[Prototype]] internal slot is the %IteratorPrototype% intrinsic object (25.1.2). In addition, %MapIteratorPrototype% has the following properties:
key
", let result be e.[[key]].value
", let result be e.[[value]]."key+value"
.The initial value of the @@toStringTag property is the String value "Map Iterator"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Map Iterator instances are ordinary objects that inherit properties from the %MapIteratorPrototype% intrinsic object. Map Iterator instances are initially created with the internal slots described in Table 50.
Internal Slot | Description |
---|---|
[[Map]] | The Map object that is being iterated. |
[[MapNextIndex]] | The integer index of the next Map data element to be examined by this iterator. |
[[MapIterationKind]] | A String value that identifies what is to be returned for each element of the iteration. The possible values are: "key" , "value" , "key+value" . |
Set objects are collections of ECMAScript language values. A distinct value may only occur once as an element of a Set’s collection. Distinct values are discriminated using the SameValueZero comparison algorithm.
Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structures used in this Set objects specification is only intended to describe the required observable semantics of Set objects. It is not intended to be a viable implementation model.
The Set constructor is the %Set% intrinsic object and the initial value of the Set
property of the global
object. When called as a constructor it creates and initializes a new Set object. Set
is not intended to be
called as a function and will throw an exception when called in that manner.
The Set
constructor is designed to be subclassable. It may be used as the value in an extends
clause of a class definition. Subclass constructors that intend to inherit the specified Set
behaviour must
include a super
call to the Set
constructor to create and initialize the subclass instance with
the internal state necessary to support the Set.prototype
built-in methods.
When the Set
function is called with optional argument iterable the
following steps are taken:
"%SetPrototype%"
, «[[SetData]]» )."add"
).The value of the [[Prototype]] internal slot of the Set constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 0), the Set constructor has the following
properties:
The initial value of Set.prototype
is the intrinsic %SetPrototype% object (23.2.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
Set[@@species]
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE Methods that create derived collection objects should call @@species to determine the constructor to use to create the derived objects. Subclass constructor may over-ride @@species to change the default constructor assignment.
The Set prototype object is the intrinsic object %SetPrototype%. The value of the [[Prototype]] internal slot of the Set prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The Set prototype object is an ordinary object. It does not have a [[SetData]] internal slot.
The following steps are taken:
The following steps are taken:
The initial value of Set.prototype.constructor
is the intrinsic object %Set%.
The following steps are taken:
NOTE The value empty is used as a specification device to indicate that an entry has been deleted. Actual implementations may take other actions such as physically removing the entry from internal data structures.
The following steps are taken:
key+value
").NOTE For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
When the forEach
method is called with one or two arguments, the following steps are
taken:
The length
property of the forEach
method is 1.
NOTE callbackfn should be a function that accepts three arguments.
forEach
calls callbackfn once for each value present in the set object, in value insertion
order. callbackfn is called only for values of the Set which actually exist; it is not called for keys that
have been deleted from the set.
If a thisArg parameter is provided, it will be used as the this value for each invocation of callbackfn. If it is not provided, undefined is used instead.
callbackfn is called with three arguments: the first two arguments are a value contained in the Set. The same value is passed for both arguments. The Set object being traversed is passed as the third argument.
The callbackfn is called with three arguments to be consistent with the call back functions used by
forEach
methods for Map and Array. For Sets, each item value is considered to be both the key and the
value.
forEach
does not directly mutate the object on which it is called but the object may be mutated by the
calls to callbackfn.
Each value is normally visited only once. However, a value will be revisited if it is deleted after it has been
visited and then re-added before the forEach
call completes. Values that are deleted after the call to
forEach
begins and before being visited are not visited unless the value is added again before the
forEach
call completes. New values added after the call to forEach
begins are visited.
The following steps are taken:
The initial value of the keys
property is the same function object as the initial value of the
values
property.
NOTE For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
Set.prototype.size
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The following steps are taken:
value
").The initial value of the @@iterator property is the same function object as the initial value of the
values
property.
The initial value of the @@toStringTag property is the String value "Set"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Set instances are ordinary objects that inherit properties from the Set prototype. Set instances also have a [[SetData]] internal slot.
A Set Iterator is an ordinary object, with the structure defined below, that represents a specific iteration over some specific Set instance object. There is not a named constructor for Set Iterator objects. Instead, set iterator objects are created by calling certain methods of Set instance objects.
Several methods of Set objects return Iterator objects. The abstract operation CreateSetIterator with arguments set and kind is used to create such iterator objects. It performs the following steps:
All Set Iterator Objects inherit properties from the %SetIteratorPrototype% intrinsic object. The %SetIteratorPrototype% intrinsic object is an ordinary object and its [[Prototype]] internal slot is the %IteratorPrototype% intrinsic object (25.1.2). In addition, %SetIteratorPrototype% has the following properties:
key+value
", then
The initial value of the @@toStringTag property is the String value "Set Iterator"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Set Iterator instances are ordinary objects that inherit properties from the %SetIteratorPrototype% intrinsic object. Set Iterator instances are initially created with the internal slots specified in Table 51.
Internal Slot | Description |
---|---|
[[IteratedSet]] | The Set object that is being iterated. |
[[SetNextIndex]] | The integer index of the next Set data element to be examined by this iterator |
[[SetIterationKind]] | A String value that identifies what is to be returned for each element of the iteration. The possible values are: "key" , "value" , "key+value" . "key" and "value" have the same meaning. |
WeakMap objects are collections of key/value pairs where the keys are objects and values may be arbitrary ECMAScript language values. A WeakMap may be queried to see if it contains a key/value pair with a specific key, but no mechanism is provided for enumerating the objects it holds as keys. If an object that is being used as the key of a WeakMap key/value pair is only reachable by following a chain of references that start within that WeakMap, then that key/value pair is inaccessible and is automatically removed from the WeakMap. WeakMap implementations must detect and remove such key/value pairs and any associated resources.
An implementation may impose an arbitrarily determined latency between the time a key/value pair of a WeakMap becomes inaccessible and the time when the key/value pair is removed from the WeakMap. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to observe a key of a WeakMap that does not require the observer to present the observed key.
WeakMap objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of key/value pairs in the collection. The data structure used in this WeakMap objects specification are only intended to describe the required observable semantics of WeakMap objects. It is not intended to be a viable implementation model.
NOTE WeakMap and WeakSets are intended to provide mechanisms for dynamically associating state with an object in a manner that does not “leak” memory resources if, in the absence of the WeakMap or WeakSet, the object otherwise became inaccessible and subject to resource reclamation by the implementation’s garbage collection mechanisms. Achieving this characteristic can be achieved by using an inverted per-object mapping of weak map instances to keys. Alternatively each weak map may internally store its key to value mappings but this approach requires coordination between the WeakMap or WeakSet implementation and the garbage collector. The following references describe mechanism that may be useful to implementations of WeakMap and WeakSets:
Barry Hayes. 1997. Ephemerons: a new finalization mechanism. In Proceedings of the 12th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications (OOPSLA '97), A. Michael Berman (Ed.). ACM, New York, NY, USA, 176-183, http://doi.acm.org/10.1145/263698.263733.
Alexandra Barros, Roberto Ierusalimschy, Eliminating Cycles in Weak Tables. Journal of Universal Computer Science - J.UCS , vol. 14, no. 21, pp. 3481-3497, 2008, http://www.jucs.org/jucs_14_21/eliminating_cycles_in_weak
The WeakMap constructor is the %WeakMap% intrinsic object and the initial value of the WeakMap
property of
the global object. When called as a constructor it creates and initializes a new WeakMap object. WeakMap
is
not intended to be called as a function and will throw an exception when called in that manner.
The WeakMap
constructor is designed to be subclassable. It may be used as the value in an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
WeakMap
behaviour must include a super
call to the WeakMap
constructor to create
and initialize the subclass instance with the internal state necessary to support the WeakMap.prototype
built-in methods.
When the WeakMap
function is called with optional argument iterable the
following steps are taken:
"%WeakMapPrototype%"
, «[[WeakMapData]]» )."set"
)."0"
)."1"
).NOTE If the parameter iterable is present, it is expected to be an object that implements an @@iterator method that returns an iterator object that produces a two element array-like object whose first element is a value that will be used as a WeakMap key and whose second element is the value to associate with that key.
The value of the [[Prototype]] internal slot of the WeakMap constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 0), the WeakMap constructor has the following
properties:
The initial value of WeakMap.prototype
is the intrinsic object %WeakMapPrototype% (23.3.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The WeakMap prototype object is the intrinsic object %WeakMapPrototype%. The value of the [[Prototype]] internal slot of the WeakMap prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The WeakMap prototype object is an ordinary object. It does not have a [[WeakMapData]] internal slot.
The initial value of WeakMap.prototype.constructor
is the intrinsic object %WeakMap%.
The following steps are taken:
NOTE The value empty is used as a specification device to indicate that an entry has been deleted. Actual implementations may take other actions such as physically removing the entry from internal data structures.
The following steps are taken:
The following steps are taken:
The following steps are taken:
The initial value of the @@toStringTag property is the String value "WeakMap"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
WeakMap instances are ordinary objects that inherit properties from the WeakMap prototype. WeakMap instances also have a [[WeakMapData]] internal slot.
WeakSet objects are collections of objects. A distinct object may only occur once as an element of a WeakSet’s collection. A WeakSet may be queried to see if it contains a specific object, but no mechanism is provided for enumerating the objects it holds. If an object that is contained by a WeakSet is only reachable by following a chain of references that start within that WeakSet, then that object is inaccessible and is automatically removed from the WeakSet. WeakSet implementations must detect and remove such objects and any associated resources.
An implementation may impose an arbitrarily determined latency between the time an object contained in a WeakSet becomes inaccessible and the time when the object is removed from the WeakSet. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to determine if a WeakSet contains a particular object that does not require the observer to present the observed object.
WeakSet objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this WeakSet objects specification is only intended to describe the required observable semantics of WeakSet objects. It is not intended to be a viable implementation model.
NOTE See the NOTE in 23.3.
The WeakSet constructor is the %WeakSet% intrinsic object and the initial value of the WeakSet
property of
the global object. When called as a constructor it creates and initializes a new WeakSet object. WeakSet
is
not intended to be called as a function and will throw an exception when called in that manner.
The WeakSet
constructor is designed to be subclassable. It may be used as the value in an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
WeakSet
behaviour must include a super
call to the WeakSet
constructor to create
and initialize the subclass instance with the internal state necessary to support the WeakSet.prototype
built-in methods.
When the WeakSet
function is called with optional argument iterable the
following steps are taken:
"%WeakSetPrototype%"
, «[[WeakSetData]]» )."add"
).The value of the [[Prototype]] internal slot of the WeakSet constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 0), the WeakSet constructor has the following
properties:
The initial value of WeakSet.prototype
is the intrinsic %WeakSetPrototype% object (23.4.3).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The WeakSet prototype object is the intrinsic object %WeakSetPrototype%. The value of the [[Prototype]] internal slot of the WeakSet prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The WeakSet prototype object is an ordinary object. It does not have a [[WeakSetData]] internal slot.
The following steps are taken:
The initial value of WeakSet.prototype.constructor
is the %WeakSet% intrinsic object.
The following steps are taken:
NOTE The value empty is used as a specification device to indicate that an entry has been deleted. Actual implementations may take other actions such as physically removing the entry from internal data structures.
The following steps are taken:
The initial value of the @@toStringTag property is the String value "WeakSet"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
WeakSet instances are ordinary objects that inherit properties from the WeakSet prototype. WeakSet instances also have a [[WeakSetData]] internal slot.
The abstract operation AllocateArrayBuffer with arguments constructor and byteLength is used to create an ArrayBuffer object. It performs the following steps:
"%ArrayBufferPrototype%"
, «[[ArrayBufferData]], [[ArrayBufferByteLength]]» ).The abstract operation IsDetachedBuffer with argument arrayBuffer performs the following steps:
The abstract operation DetachArrayBuffer with argument arrayBuffer performs the following steps:
NOTE Detaching an ArrayBuffer instance disassociates the Data Block used as its backing store from the instance and sets the byte length of the buffer to 0. No operations defined by this specification use the DetachArrayBuffer abstract operation. However, an ECMAScript implementation or host environment may define such operations.
The abstract operation CloneArrayBuffer takes three parameters, an ArrayBuffer srcBuffer, an integer srcByteOffset and optionally a constructor function cloneConstructor. It creates a new ArrayBuffer whose data is a copy of srcBuffer’s data starting at srcByteOffset. This operation performs the following steps:
The abstract operation GetValueFromBuffer takes four parameters, an ArrayBuffer arrayBuffer, an integer byteIndex, a String type, and optionally a Boolean isLittleEndian. This operation performs the following steps:
"Float32"
, then
"Float64"
, then
"U"
, then
The abstract operation SetValueInBuffer takes five parameters, an ArrayBuffer arrayBuffer, an integer byteIndex, a String type, a Number value, and optionally a Boolean isLittleEndian. This operation performs the following steps:
"Float32"
, then
"Float64"
, then
The ArrayBuffer constructor is the %ArrayBuffer% intrinsic object and the initial value of the ArrayBuffer
property of the global object. When called as a constructor it creates and initializes a new ArrayBuffer object.
ArrayBuffer
is not intended to be called as a function and will throw an exception when called in that
manner.
The ArrayBuffer
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
ArrayBuffer
behaviour must include a super
call to the ArrayBuffer
constructor to
create and initialize subclass instances with the internal state necessary to support the ArrayBuffer.prototype
built-in methods.
ArrayBuffer called with argument length performs the following steps:
The value of the [[Prototype]] internal slot of the ArrayBuffer constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides its length
property (whose value is 1), the ArrayBuffer constructor has the following
properties:
The isView function takes one argument arg, and performs the following steps are taken:
The initial value of ArrayBuffer.prototype is the intrinsic object %ArrayBufferPrototype% (24.1.4).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
ArrayBuffer[@@species]
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE ArrayBuffer prototype methods normally use their this
object’s
constructor to create a derived object. However, a subclass constructor may over-ride that default behaviour by
redefining its @@species property.
The ArrayBuffer prototype object is the intrinsic object %ArrayBufferPrototype%. The value of the [[Prototype]] internal slot of the ArrayBuffer prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The ArrayBuffer prototype object is an ordinary object. It does not have an [[ArrayBufferData]] or [[ArrayBufferByteLength]] internal slot.
ArrayBuffer.prototype.byteLength
is an accessor property whose set accessor function
is undefined. Its get accessor function performs the following steps:
The initial value of ArrayBuffer.prototype.constructor
is the intrinsic object %ArrayBuffer%.
The following steps are taken:
The initial value of the @@toStringTag property is the String value "ArrayBuffer"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
ArrayBuffer instances inherit properties from the ArrayBuffer prototype object. ArrayBuffer instances each have an [[ArrayBufferData]] internal slot and an [[ArrayBufferByteLength]] internal slot.
ArrayBuffer instances whose [[ArrayBufferData]] is null are considered to be detached and all operators to access or modify data contained in the ArrayBuffer instance will fail.
The abstract operation GetViewValue with arguments view, requestIndex, isLittleEndian, and type is used by functions on DataView instances is to retrieve values from the view’s buffer. It performs the following steps:
The abstract operation SetViewValue with arguments view, requestIndex, isLittleEndian, type, and value is used by functions on DataView instances to store values into the view’s buffer. It performs the following steps:
NOTE The algorithms for GetViewValue and SetViewValue are identical except for their final steps.
The DataView constructor is the %DataView% intrinsic object and the initial value of the DataView
property
of the global object. When called as a constructor it creates and initializes a new DataView object. DataView
is not intended to be called as a function and will throw an exception when called in that manner.
The DataView
constructor is designed to be subclassable. It may be used as the value of an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
DataView
behaviour must include a super
call to the DataView
constructor to create
and initialize subclass instances with the internal state necessary to support the DataView.prototype
built-in methods.
DataView
called with arguments buffer, byteOffset, and length performs the following steps:
"%DataViewPrototype%"
, «[[DataView]], [[ViewedArrayBuffer]], [[ByteLength]],
[[ByteOffset]]» ).The value of the [[Prototype]] internal slot of the
DataView
constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 3), the DataView constructor has the following properties:
The initial value of DataView.prototype
is the intrinsic object %DataViewPrototype% (24.2.4).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The DataView prototype object is the intrinsic object %DataViewPrototype%. The value of the [[Prototype]] internal slot of the DataView prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The DataView prototype object is an ordinary object. It does not have a [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], or [[ByteOffset]] internal slot.
DataView.prototype.buffer
is an accessor property whose set accessor function is
undefined. Its get accessor function performs the following steps:
DataView
.prototype.byteLength
is an accessor property whose set accessor
function is undefined. Its get accessor function performs the following steps:
DataView
.prototype.byteOffset
is an accessor property whose set accessor
function is undefined. Its get accessor function performs the following steps:
The initial value of DataView.prototype.constructor
is the intrinsic object %DataView%.
When the getFloat32
method is called with argument byteOffset and optional
argument littleEndian the following steps are taken:
"Float32"
).When the getFloat64
method is called with argument byteOffset and optional
argument littleEndian the following steps are taken:
"Float64"
).When the getInt8
method is called with argument byteOffset the following
steps are taken:
"Int8"
).When the getInt16
method is called with argument byteOffset and optional
argument littleEndian the following steps are taken:
"Int16"
).When the getInt32
method is called with argument byteOffset and optional
argument littleEndian the following steps are taken:
"Int32"
).When the getUint8
method is called with argument byteOffset the following
steps are taken:
"Uint8"
).When the getUint16
method is called with argument byteOffset and optional
argument littleEndian the following steps are taken:
"Uint16"
).When the getUint32
method is called with argument byteOffset and optional
argument littleEndian the following steps are taken:
"Uint32"
).When the setFloat32
method is called with arguments byteOffset and
value and optional argument littleEndian the following steps are taken:
"Float32"
, value).When the setFloat64
method is called with arguments byteOffset and
value and optional argument littleEndian the following steps are taken:
"Float64"
, value).When the setInt8
method is called with arguments byteOffset and
value the following steps are taken:
"Int8"
,
value).When the setInt16
method is called with arguments byteOffset and
value and optional argument littleEndian the following steps are taken:
"Int16"
, value).When the setInt32
method is called with arguments byteOffset and
value and optional argument littleEndian the following steps are taken:
"Int32"
, value).When the setUint8
method is called with arguments byteOffset and
value the following steps are taken:
"Uint8"
,
value).When the setUint16
method is called with arguments byteOffset and
value and optional argument littleEndian the following steps are taken:
"Uint16"
, value).When the setUint32
method is called with arguments byteOffset and
value and optional argument littleEndian the following steps are taken:
"Uint32"
, value).The initial value of the @@toStringTag property is the String value "DataView"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
DataView instances are ordinary objects that inherit properties from the DataView prototype object. DataView instances each have [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], and [[ByteOffset]] internal slots.
NOTE The value of the [[DataView]] internal slot is not used within this specification. The simple
presence of that internal slot is used within the
specification to identify objects created using the DataView
constructor.
The JSON object is the %JSON% intrinsic object and the initial value of the JSON
property of the global
object. The JSON object is a single ordinary object that contains two functions, parse and stringify, that are
used to parse and construct JSON texts. The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange format
used in this specification is exactly that described by ECMA-404.
Conforming implementations of JSON.parse
and JSON.stringify
must support the exact interchange format described in the ECMA-404
specification without any deletions or extensions to the format.
The value of the [[Prototype]] internal slot of the JSON object is the intrinsic object %ObjectPrototype% (19.1.3). The value of the [[Extensible]] internal slot of the JSON object is set to true.
The JSON object does not have a [[Construct]] internal method; it is not possible to use the JSON object as a constructor
with the new
operator.
The JSON object does not have a [[Call]] internal method; it is not possible to invoke the JSON object as a function.
The parse
function parses a JSON text (a JSON-formatted String) and produces an ECMAScript value. The JSON
format is a subset of the syntax for ECMAScript literals, Array Initializers and Object Initializers. After parsing, JSON
objects are realized as ECMAScript objects. JSON arrays are realized as ECMAScript Array instances. JSON strings, numbers,
booleans, and null are realized as ECMAScript Strings, Numbers, Booleans, and null.
The optional reviver parameter is a function that takes two parameters, key and value. It can filter and transform the results. It is called with each of the key/value pairs produced by the parse, and its return value is used instead of the original value. If it returns what it received, the structure is not modified. If it returns undefined then the property is deleted from the result.
"("
, JText, and ");"
.JSON allows Unicode code units 0x2028 (LINE SEPARATOR) and 0x2029 (PARAGRAPH SEPARATOR) to directly appear in String literals without using an escape sequence. This is enabled by using the following alternative definition of DoubleStringCharacter when parsing scriptText in step 5:
"
or \
or U+0000 through U+001F\
EscapeSequenceThe SV of DoubleStringCharacter :: SourceCharacter but not one of "
or \
or U+0000 through U+001F
is the UTF16Encoding (10.1.1) of the code point
value of SourceCharacter.
NOTE The syntax of a valid JSON text is a subset of the ECMAScript PrimaryExpression syntax. Hence a valid JSON text is also a valid PrimaryExpression. Step 3 above verifies that JText conforms to that subset. When scriptText is parsed and evaluated as a Script the result will be either a String, Number, Boolean, or Null primitive value or an Object defined as if by an ArrayLiteral or ObjectLiteral.
The abstract operation InternalizeJSONProperty is a recursive abstract operation that takes two parameters: a holder object and the String name of a property in that object. InternalizeJSONProperty uses the value of reviver that was originally passed to the above parse function.
"length"
)).It is not permitted for a conforming implementation of JSON.parse
to extend
the JSON grammars. If an implementation wishes to support a modified or extended JSON interchange format it must do so by
defining a different parse function.
NOTE In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.
The stringify
function returns a String in UTF-16 encoded JSON format representing an ECMAScript value. It
can take three parameters. The value parameter is an ECMAScript value, which is usually an object or array,
although it can also be a String, Boolean, Number or null. The optional replacer parameter is either a
function that alters the way objects and arrays are stringified, or an array of Strings and Numbers that acts as a white
list for selecting the object properties that will be stringified. The optional space parameter is a String or
Number that allows the result to have white space injected into it to improve human readability.
These are the steps in stringifying an object:
"length"
)).NOTE 1 JSON structures are allowed to be nested to any depth, but they must be acyclic. If value is or contains a cyclic structure, then the stringify function must throw a TypeError exception. This is an example of a value that cannot be stringified:
a = [];
a[0] = a;
my_text = JSON.stringify(a); // This must throw a TypeError.
NOTE 2 Symbolic primitive values are rendered as follows:
null
.true
.false
.NOTE 3 String values are wrapped in QUOTATION MARK ("
) code units. The code
units "
and \
are escaped with \
prefixes. Control characters code units are
replaced with escape sequences \u
HHHH, or with the shorter forms, \b
(BACKSPACE),
\f
(FORM FEED), \n
(LINE FEED), \r
(CARRIAGE RETURN), \t
(CHARACTER
TABULATION).
NOTE 4 Finite numbers are stringified as if by calling ToString(number). NaN and Infinity regardless of sign are
represented as the String null
.
NOTE 5 Values that do not have a JSON representation (such as undefined and functions)
do not produce a String. Instead they produce the undefined value. In arrays these values are
represented as the String null
. In objects an unrepresentable value causes the property to be excluded from
stringification.
NOTE 6 An object is rendered as U+007B (LEFT CURLY BRACKET) followed by zero or more properties, separated with a U+002C (COMMA), closed with a U+007D (RIGHT CURLY BRACKET). A property is a quoted String representing the key or property name, a U+003A (COLON), and then the stringified property value. An array is rendered as an opening U+005B (LEFT SQUARE BRACKET followed by zero or more values, separated with a U+002C (COMMA), closed with a U+005D (RIGHT SQUARE BRACKET).
The abstract operation SerializeJSONProperty with arguments key, and holder has access to ReplacerFunction
from the invocation of the stringify
method. Its algorithm is as follows:
"toJSON"
)."null"
."true"
."false"
."null"
.The abstract operation QuoteJSONString with argument value wraps a String value in QUOTATION MARK code units and escapes certain other code units within it.
BACKSPACE | "b" |
FORM FEED (FF) | "f" |
LINE FEED (LF) | "n" |
CARRIAGE RETURN (CR) | "r" |
LINE TABULATION | "t" |
"u"
.The abstract operation SerializeJSONObject with argument value serializes an object. It
has access to the stack, indent, gap, and PropertyList values of
the current invocation of the stringify
method.
":"
."{}"
."{"
, properties, and
"}"
."{"
, code unit 0x000A (LINE FEED),
indent, properties, code unit 0x000A, stepback, and "}"
.The abstract operation SerializeJSONArray with argument value serializes an array. It
has access to the stack, indent, and gap values of the current invocation of the
stringify
method.
"length"
))."null"
to partial."[]"
."["
, properties, and
"]"
."["
, code unit 0x000A (LINE FEED),
indent, properties, code unit 0x000A, stepback, and "]"
.NOTE The representation of arrays includes only the elements between zero and
array.length
– 1 inclusive. Properties whose keys
are not array indexes are excluded from the stringification. An array is stringified as an opening LEFT SQUARE BRACKET,
elements separated by COMMA, and a closing RIGHT SQUARE BRACKET.
The initial value of the @@toStringTag property is the String value "JSON"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
An interface is a set of property keys whose associated values match a specific specification. Any object that provides all the properties as described by an interface’s specification conforms to that interface. An interface is not represented by a distinct object. There may be many separately implemented objects that conform to any interface. An individual object may conform to multiple interfaces.
The Iterable interface includes the property described in Table 52:
Property | Value | Requirements |
---|---|---|
@@iterator |
A function that returns an Iterator object. | The returned object must conform to the Iterator interface. |
An object that implements the Iterator interface must include the property in Table 53. Such objects may also implement the properties in Table 54.
Property | Value | Requirements |
---|---|---|
next |
A function that returns an IteratorResult object. | The returned object must conform to the IteratorResult interface. If a previous call to the next method of an Iterator has returned an IteratorResult object whose done property is true, then all subsequent calls to the next method of that object should also return an IteratorResult object whose done property is true. However, this requirement is not enforced. |
NOTE 1 Arguments may be passed to the next function but their interpretation and validity is dependent upon the target Iterator. The for-of statement and other common users of Iterators do not pass any arguments, so Iterator objects that expect to be used in such a manner must be prepared to deal with being called with no arguments.
Property | Value | Requirements |
---|---|---|
return |
A function that returns an IteratorResult object. | The returned object must conform to the IteratorResult interface. Invoking this method notifies the Iterator object that the caller does not intend to make any more next method calls to the Iterator. The returned IteratorResult object will typically have a done property whose value is true, and a value property with the value passed as the argument of the return method. However, this requirement is not enforced. |
throw |
A function that returns an IteratorResult object. | The returned object must conform to the IteratorResult interface. Invoking this method notifies the Iterator object that the caller has detected an error condition. The argument may be used to identify the error condition and typically will be an exception object. A typical response is to throw the value passed as the argument. If the method does not throw , the returned IteratorResult object will typically have a done property whose value is true. |
NOTE 2 Typically callers of these methods should check for their existence before invoking
them. Certain ECMAScript language features including for
-of
, yield*
, and array
destructuring call these methods after performing an existence check. Most ECMAScript library functions that accept
Iterable objects as arguments also conditionally call them.
The IteratorResult interface includes the properties listed in Table 55:
Property | Value | Requirements |
---|---|---|
done |
Either true or false. | This is the result status of an iterator next method call. If the end of the iterator was reached done is true. If the end was not reached done is false and a value is available. If a done property (either own or inherited) does not exist, it is consider to have the value false. |
value |
Any ECMAScript language value. | If done is false, this is the current iteration element value. If done is true, this is the return value of the iterator, if it supplied one. If the iterator does not have a return value, value is undefined. In that case, the value property may be absent from the conforming object if it does not inherit an explicit value property. |
The value of the [[Prototype]] internal slot of the %IteratorPrototype% object is the intrinsic object %ObjectPrototype% (19.1.3). The %IteratorPrototype% object is an ordinary object. The initial value of the [[Extensible]] internal slot of the %IteratorPrototype% object is true.
NOTE All objects defined in this specification that implement the Iterator interface also inherit from %IteratorPrototype%. ECMAScript code may also define objects that inherit from %IteratorPrototype%.The %IteratorPrototype% object provides a place where additional methods that are applicable to all iterator objects may be added.
The following expression is one way that ECMAScript code can access the %IteratorPrototype% object:
Object.getPrototypeOf(Object.getPrototypeOf([][Symbol.iterator]()))
The following steps are taken:
The value of the name
property of this function is "[Symbol.iterator]"
.
Generator Function objects are constructor functions that are usually created by evaluating GeneratorDeclaration, GeneratorExpression, and GeneratorMethod syntactic productions. They may also be created by calling the %GeneratorFunction% intrinsic.
The GeneratorFunction
constructor is the %GeneratorFunction% intrinsic. When
GeneratorFunction
is called as a function rather than as a constructor, it creates and initializes a new
GeneratorFunction object. Thus the function call GeneratorFunction
(…)
is
equivalent to the object creation expression new GeneratorFunction
(…)
with
the same arguments.
GeneratorFunction
is designed to be subclassable. It may be used as the value of an extends
clause of a class definition. Subclass constructors that intend to inherit the specified GeneratorFunction
behaviour must include a super
call to the GeneratorFunction
constructor to create and
initialize subclass instances with the internal slots necessary for built-in GeneratorFunction behaviour. All ECMAScript
syntactic forms for defining generator function objects create direct instances of GeneratorFunction
. There
is no syntactic means to create instances of GeneratorFunction
subclasses.
The last argument specifies the body (executable code) of a generator function; any preceding arguments specify formal parameters.
When the GeneratorFunction
function is called with some arguments p1,
p2, … , pn, body (where n might be 0, that is, there are no “p” arguments, and where body might also not be
provided), the following steps are taken:
"generator"
,
args).NOTE See NOTE for 19.2.1.1.
The GeneratorFunction
constructor is a standard built-in function object that inherits from the
Function
constructor. The value of the [[Prototype]] internal slot of the GeneratorFunction
constructor
is the intrinsic object %Function%.
The value of the [[Extensible]] internal slot of the GeneratorFunction constructor is true.
The value of the name
property of the GeneratorFunction is "GeneratorFunction"
.
The GeneratorFunction
constructor has the following properties:
This is a data property with a value of 1. This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The initial value of GeneratorFunction.prototype
is the intrinsic object %Generator%.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The GeneratorFunction prototype object is an ordinary object. It is not a function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed in Table 27 or Table 56. In addition to being the value of the prototype property of the %GeneratorFunction% intrinsic, it is the %Generator% intrinsic (see Figure 2).
The value of the [[Prototype]] internal slot of the GeneratorFunction prototype object is the %FunctionPrototype% intrinsic object. The initial value of the [[Extensible]] internal slot of the GeneratorFunction prototype object is true.
The initial value of GeneratorFunction.prototype.constructor
is the intrinsic object
%GeneratorFunction%.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The value of GeneratorFunction.prototype.prototype
is the %GeneratorPrototype% intrinsic object.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The initial value of the @@toStringTag property is the String value "GeneratorFunction"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Every GeneratorFunction instance is an ECMAScript function object and
has the internal slots listed in Table 27. The value of the [[FunctionKind]] internal slot for all such instances is
"generator"
.
Each GeneratorFunction instance has the following own properties:
The value of the length
property is an integer that indicates the typical number of arguments expected by
the GeneratorFunction. However, the language permits the function to be invoked with some other number of arguments. The
behaviour of a GeneratorFunction when invoked on a number of arguments other than the number specified by its
length
property depends on the function.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The specification for the name
property of Function instances given in 19.2.4.2 also applies to GeneratorFunction instances.
Whenever a GeneratorFunction instance is created another ordinary object is also created and is the initial value of
the generator function’s prototype
property. The value of the prototype property is used to initialize
the [[Prototype]] internal slot of a newly created Generator
object when the generator function object is invoked using either [[Call]] or [[Construct]].
This property has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: false }.
NOTE Unlike function instances, the object that is the value of the a
GeneratorFunction’s prototype
property does not have a constructor
property whose value
is the GeneratorFunction instance.
A Generator object is an instance of a generator function and conforms to both the Iterator and Iterable interfaces.
Generator instances directly inherit properties from the object that is the value of the prototype
property
of the Generator function that created the instance. Generator instances indirectly inherit properties from the Generator
Prototype intrinsic, %GeneratorPrototype%.
The Generator prototype object is the %GeneratorPrototype% intrinsic. It is also the initial value of the
prototype
property of the %Generator% intrinsic (the GeneratorFunction.prototype).
The Generator prototype is an ordinary object. It is not a Generator instance and does not have a [[GeneratorState]] internal slot.
The value of the [[Prototype]] internal slot of the Generator prototype object is the intrinsic object %IteratorPrototype% (25.1.2). The initial value of the [[Extensible]] internal slot of the Generator prototype object is true.
All Generator instances indirectly inherit properties of the Generator prototype object.
The initial value of Generator.prototype.constructor
is the intrinsic object %Generator%.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
The next
method performs the following steps:
The return
method performs the following steps:
The throw
method performs the following steps:
The initial value of the @@toStringTag property is the String value "Generator"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Generator instances are initially created with the internal slots described in Table 56.
Internal Slot | Description |
---|---|
[[GeneratorState]] | The current execution state of the generator. The possible values are: undefined, "suspendedStart" , "suspendedYield" , "executing" , and "completed" . |
[[GeneratorContext]] | The execution context that is used when executing the code of this generator. |
The abstract operation GeneratorStart with arguments generator and generatorBody performs the following steps:
"completed"
."completed"
state it never leaves it and its associated execution context is never resumed. Any execution state associated with
generator can be discarded at this point."suspendedStart"
.The abstract operation GeneratorValidate with argument generator performs the following steps:
"executing"
, throw a TypeError exception.The abstract operation GeneratorResume with arguments generator and value performs the following steps:
"completed"
, return CreateIterResultObject(undefined, true)."suspendedStart"
or
"suspendedYield"
."executing"
.The abstract operation GeneratorResumeAbrupt with arguments generator and abruptCompletion performs the following steps:
"suspendedStart"
, then
"completed"
."completed"
state it never leaves it and its associated execution context is never resumed. Any execution state associated with
generator can be discarded at this point."completed"
."completed"
, then
"suspendedYield"
."executing"
.The abstract operation GeneratorYield with argument iterNextObj performs the following steps:
"suspendedYield"
.A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) computation.
Any Promise object is in one of three mutually exclusive states: fulfilled, rejected, and pending:
A promise p
is fulfilled if p.then(f, r)
will immediately enqueue a Job to call the
function f
.
A promise p
is rejected if p.then(f, r)
will immediately enqueue a Job to call the function
r
.
A promise is pending if it is neither fulfilled nor rejected.
A promise is said to be settled if it is not pending, i.e. if it is either fulfilled or rejected.
A promise is resolved if it is settled or if it has been “locked in” to match the state of another promise. Attempting to resolve or reject a resolved promise has no effect. A promise is unresolved if it is not resolved. An unresolved promise is always in the pending state. A resolved promise may be pending, fulfilled or rejected.
A PromiseCapability is a Record value used to encapsulate a promise object along with the functions that are capable of resolving or rejecting that promise object. PromiseCapability records are produced by the NewPromiseCapability abstract operation.
PromiseCapability Records have the fields listed in Table 57.
Field Name | Value | Meaning |
---|---|---|
[[Promise]] | An object | An object that is usable as a promise. |
[[Resolve]] | A function object | The function that is used to resolve the given promise object. |
[[Reject]] | A function object | The function that is used to reject the given promise object. |
IfAbruptRejectPromise is a short hand for a sequence of algorithm steps that use a PromiseCapability record. An algorithm step of the form:
means the same thing as:
The PromiseReaction is a Record value used to store information about how a promise should react when it becomes
resolved or rejected with a given value. PromiseReaction records are created by the then
method of the
Promise prototype, and are used by a PromiseReactionJob.
PromiseReaction records have the fields listed in Table 58.
Field Name | Value | Meaning |
---|---|---|
[[Capabilities]] | A PromiseCapability record | The capabilities of the promise for which this record provides a reaction handler. |
[[Handler]] | A function object or a String | The function that should be applied to the incoming value, and whose return value will govern what happens to the derived promise. If [[Handler]] is "Identity" it is equivalent to a function that simply returns its first argument. If [[Handler]] is "Thrower" it is equivalent to a function that throws its first argument as an exception. |
When CreateResolvingFunctions is performed with argument promise, the following steps are taken:
A promise reject function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal slots.
When a promise reject function F is called with argument reason, the following steps are taken:
The length
property of a promise reject function is 1.
A promise resolve function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal slots.
When a promise resolve function F is called with argument resolution, the following steps are taken:
"then"
)."PromiseJobs"
, PromiseResolveThenableJob, «promise,
resolution, thenAction»)The length
property of a promise resolve function is 1.
When the FulfillPromise abstract operation is called with arguments promise and value the following steps are taken:
"pending"
."fulfilled"
.The abstract operation NewPromiseCapability takes a constructor function, and attempts to use
that constructor function in the fashion of the built-in Promise
constructor to create a Promise object and
extract its resolve and reject functions. The promise plus the resolve and reject functions are used to initialize a new
PromiseCapability record which is returned as the value of this abstract operation.
Promise
constructor (see
25.4.3.1).NOTE This abstract operation supports Promise subclassing, as it is generic on any constructor that calls a passed executor function argument in the same way as the Promise constructor. It is used to generalize static methods of the Promise constructor to any subclass.
A GetCapabilitiesExecutor function is an anonymous built-in function that has a [[Capability]] internal slot.
When a GetCapabilitiesExecutor function F is called with arguments resolve and reject the following steps are taken:
The length
property of a GetCapabilitiesExecutor function is 2.
The abstract operation IsPromise checks for the promise brand on an object.
When the RejectPromise abstract operation is called with arguments promise and reason the following steps are taken:
"pending"
."rejected"
.The abstract operation TriggerPromiseReactions takes a collection of PromiseReactionRecords and enqueues a new Job for each record. Each such Job processes the [[Handler]] of the PromiseReactionRecord, and if the [[Handler]] is a function calls it passing the given argument.
"PromiseJobs"
, PromiseReactionJob, «reaction,
argument»).The job PromiseReactionJob with parameters reaction and argument applies the appropriate handler to the incoming value, and uses the handler's return value to resolve or reject the derived promise associated with that handler.
"Identity"
, let handlerResult be NormalCompletion(argument)."Thrower"
, let handlerResult be Completion{[[type]]: throw, [[value]]: argument, [[target]]: empty}.The job PromiseResolveThenableJob with parameters promiseToResolve, thenable, and then performs the following steps:
NOTE This Job uses the supplied thenable and its then
method to resolve the
given promise. This process must take place as a Job to ensure that the evaluation of the then
method
occurs after evaluation of any surrounding code has completed.
The Promise constructor is the %Promise% intrinsic object and the initial value of the Promise
property of
the global object. When called as a constructor it creates and initializes a new Promise object. Promise
is
not intended to be called as a function and will throw an exception when called in that manner.
The Promise
constructor is designed to be subclassable. It may be used as the value in an
extends
clause of a class definition. Subclass constructors that intend to inherit the specified
Promise
behaviour must include a super
call to the Promise
constructor to create
and initialize the subclass instance with the internal state necessary to support the Promise
and
Promise.prototype
built-in methods.
When the Promise
function is called with argument executor the following
steps are taken:
"%PromisePrototype%"
, «[[PromiseState]], [[PromiseResult]], [[PromiseFulfillReactions]],
[[PromiseRejectReactions]]» )."pending"
.NOTE The executor argument must be a function object. It is called for initiating and reporting completion of the possibly deferred action represented by this Promise object. The executor is called with two arguments: resolve and reject. These are functions that may be used by the executor function to report eventual completion or failure of the deferred computation. Returning from the executor function does not mean that the deferred action has been completed but only that the request to eventually perform the deferred action has been accepted.
The resolve function that is passed to an executor function accepts a single argument. The executor code may eventually call the resolve function to indicate that it wishes to resolve the associated Promise object. The argument passed to the resolve function represents the eventual value of the deferred action and can be either the actual fulfillment value or another Promise object which will provide the value if it is fulfilled.
The reject function that is passed to an executor function accepts a single argument. The
executor code may eventually call the reject function to indicate that the associated Promise is
rejected and will never be fulfilled. The argument passed to the reject function is used as the rejection
value of the promise. Typically it will be an Error
object.
The resolve and reject functions passed to an executor function by the Promise constructor have the capability to actually resolve and reject the associated promise. Subclasses may have different constructor behaviour that passes in customized values for resolve and reject.
The value of the [[Prototype]] internal slot of the
Promise
constructor is the intrinsic object %FunctionPrototype% (19.2.3).
Besides the length
property (whose value is 1), the Promise constructor has the following properties:
The all
function returns a new promise which is fulfilled with an array of
fulfillment values for the passed promises, or rejects with the reason of the first passed promise that rejects. It
resolves all elements of the passed iterable to promises as it runs this algorithm.
NOTE The all
function requires its this value to be a constructor
function that supports the parameter conventions of the Promise
constructor.
When the PerformPromiseAll abstract operation is called with arguments iteratorRecord, constructor, and resultCapability the following steps are taken:
"resolve"
,
«nextValue»)."then"
,
«resolveElement, resultCapability.[[Reject]]»).A Promise.all resolve element function is an anonymous built-in function that is used to resolve a specific Promise.all element. Each Promise.all resolve element function has [[Index]], [[Values]], [[Capabilities]], [[RemainingElements]], and [[AlreadyCalled]] internal slots.
When a Promise.all resolve element function F is called with argument x, the following steps are taken:
The length
property of a Promise.all resolve element function is
1.
The initial value of Promise.prototype
is the intrinsic object %PromisePrototype% (25.4.5).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The race
function returns a new promise which is settled in the same way as the
first passed promise to settle. It resolves all elements of the passed iterable to promises as it runs this algorithm.
NOTE 1 If the iterable argument is empty or if none of the promises in iterable ever settle then the pending promise returned by this method will never be settled
NOTE 2 The race
function expects its this value to be a constructor
function that supports the parameter conventions of the Promise
constructor. It also expects that its
this value provides a resolve
method.
When the PerformPromiseRace abstract operation is called with arguments iteratorRecord, promiseCapability, and C the following steps are taken:
"resolve"
,
«nextValue»)."then"
,
«promiseCapability.[[Resolve]], promiseCapability.[[Reject]]»).The reject
function returns a new promise rejected with the passed argument.
NOTE The reject
function expects its this value to be a constructor
function that supports the parameter conventions of the Promise
constructor.
The resolve
function returns either a new promise resolved with the passed argument,
or the argument itself if the argument is a promise produced by this constructor.
"constructor"
).NOTE The resolve
function expects its this value to be a constructor
function that supports the parameter conventions of the Promise
constructor.
Promise[@@species]
is an accessor property whose set accessor function is undefined. Its get accessor function performs the following steps:
The value of the name
property of this function is "get [Symbol.species]"
.
NOTE Promise prototype methods normally use their this
object’s
constructor to create a derived object. However, a subclass constructor may over-ride that default behaviour by
redefining its @@species property.
The Promise prototype object is the intrinsic object %PromisePrototype%. The value of the [[Prototype]] internal slot of the Promise prototype object is the intrinsic object %ObjectPrototype% (19.1.3). The Promise prototype object is an ordinary object. It does not have a [[PromiseState]] internal slot or any of the other internal slots of Promise instances.
When the catch
method is called with argument onRejected the following
steps are taken:
"then"
, «undefined,
onRejected»).The initial value of Promise.prototype.constructor
is the intrinsic object %Promise%.
When the then
method is called with arguments onFulfilled and
onRejected the following steps are taken:
The abstract operation PerformPromiseThen performs the “then” operation on promise using onFulfilled and onRejected as its settlement actions. The result is resultCapability’s promise.
"Identity"
."Thrower"
."pending"
,
"fulfilled"
,
"PromiseJobs"
, PromiseReactionJob, «fulfillReaction,
value»)."rejected"
,
"PromiseJobs"
, PromiseReactionJob, «rejectReaction,
reason»).The initial value of the @@toStringTag property is the String value "Promise"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
Promise instances are ordinary objects that inherit properties from the Promise prototype object (the intrinsic, %PromisePrototype%). Promise instances are initially created with the internal slots described in Table 59.
Internal Slot | Description |
---|---|
[[PromiseState]] | A String value that governs how a promise will react to incoming calls to its then method. The possible values are: "pending" , "fulfilled" , and "rejected" . |
[[PromiseResult]] | The value with which the promise has been fulfilled or rejected, if any. Only meaningful if [[PromiseState]] is not "pending" . |
[[PromiseFulfillReactions]] | A List of PromiseReaction records to be processed when/if the promise transitions from the "pending" state to the "fulfilled" state. |
[[PromiseRejectReactions]] | A List of PromiseReaction records to be processed when/if the promise transitions from the "pending" state to the "rejected" state. |
The Reflect object is the %Reflect% intrinsic object and the initial value of the Reflect
property of the
global object.The Reflect object is an ordinary object.
The value of the [[Prototype]] internal slot of the Reflect object is the intrinsic object %ObjectPrototype% (19.1.3).
The Reflect object is not a function object. It does not have a [[Construct]] internal method; it is not possible to use
the Reflect object as a constructor with the new
operator. The Reflect object also does not have a [[Call]]
internal method; it is not possible to invoke the Reflect object as a function.
When the apply
function is called with arguments target, thisArgument, and argumentsList the following steps are taken:
When the construct
function is called with arguments target,
argumentsList, and newTarget the following steps are taken:
The length
property of the construct
function is 2.
When the defineProperty
function is called with arguments target, propertyKey, and attributes the following steps are taken:
When the deleteProperty
function is called with arguments target and propertyKey, the following steps are taken:
When the enumerate
function is called with argument target the following
steps are taken:
When the get
function is called with arguments target, propertyKey, and receiver the following steps are taken:
The length
property of the get
function is 2.
When the getOwnPropertyDescriptor
function is called with arguments target and propertyKey, the following steps are taken:
When the getPrototypeOf
function is called with argument target the
following steps are taken:
When the has
function is called with arguments target and propertyKey, the following steps are taken:
When the isExtensible
function is called with argument target the following
steps are taken:
When the ownKeys
function is called with argument target the following steps
are taken:
When the preventExtensions
function is called with argument target, the
following steps are taken:
When the set
function is called with arguments target, V, propertyKey, and receiver the following steps are taken:
The length
property of the set
function is 3.
When the setPrototypeOf
function is called with arguments target and propertyKey, the following steps are taken:
The Proxy constructor is the %Proxy% intrinsic object and the initial value of the Proxy
property of the
global object. When called as a constructor it creates and initializes a new proxy exotic object. Proxy
is
not intended to be called as a function and will throw an exception when called in that manner.
When Proxy
is called with arguments target and handler performs
the following steps:
The value of the [[Prototype]] internal slot of the
Proxy
constructor is the intrinsic object %FunctionPrototype% (19.2.3).
The Proxy
constructor does not have a prototype
property because proxy exotic objects do not
have a [[Prototype]] internal slot that requires
initialization.
Besides the length
property (whose value is 2), the Proxy
constructor has the
following properties:
The Proxy.revocable
function is used to create a revocable Proxy object. When
Proxy.revocable
is called with arguments target and handler the following steps are
taken:
"proxy"
,
p)."revoke"
,
revoker).A Proxy revocation function is an anonymous function that has the ability to invalidate a specific Proxy object.
Each Proxy revocation function has a [[RevocableProxy]] internal slot.
When a Proxy revocation function, F, is called the following steps are taken:
A Module Namespace Object is a module namespace exotic object that provides runtime property-based access to a module’s exported bindings. There is no constructor function for Module Namespace Objects. Instead, such an object is created for each module that is imported by an ImportDeclaration that includes a NameSpaceImport (See 15.2.2).
In addition to the properties specified in 9.4.6 each Module Namespace Object has the own following properties:
The initial value of the @@toStringTag property is the String value "Module"
.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true }.
When the @@iterator method is called with no arguments, the following steps are taken:
The value of the name
property of this function is "[Symbol.iterator]"
.
*
PostAsteriskCommentCharsopt*
PostAsteriskCommentCharsoptbreak |
do |
in |
typeof |
case |
else |
instanceof |
var |
catch |
export |
new |
void |
class |
extends |
return |
while |
const |
finally |
super |
with |
continue |
for |
switch |
yield |
debugger |
function |
this |
|
default |
if |
throw |
|
delete |
import |
try |
await
is only treated as a FutureReservedWord when Module is
the goal symbol of the syntactic grammar.
The following tokens are also considered to be FutureReservedWords when parsing strict mode code (see 10.2.1).
implements |
package |
protected |
|
interface |
private |
public |
{ |
} |
( |
) |
[ |
] |
. |
; |
, |
< |
> |
<= |
>= |
== |
!= |
=== |
!== |
|
+ |
- |
* |
% |
++ |
-- |
<< |
>> |
>>> |
& |
| |
^ |
! |
~ |
&& |
|| |
? |
: |
= |
+= |
-= |
*= |
%= |
<<= |
>>= |
>>>= |
&= |
|= |
^= |
=> |
.
DecimalDigitsopt ExponentPartopt.
DecimalDigits ExponentPartopt"
or \
or LineTerminator\
EscapeSequence'
or \
or LineTerminator\
EscapeSequence0
[lookahead ∉ DecimalDigit]*
or \
or /
or [
\
or /
or [
]
or \
$
[lookahead ≠ { ]\
EscapeSequence`
or \
or $
or LineTerminatorBindingIdentifier[Yield] : See 12.1
Identifier
[~Yield] yield
this
(
Expression[In, ?Yield] )
(
)
(
...
BindingIdentifier[?Yield] )
(
Expression[In, ?Yield] ,
...
BindingIdentifier[?Yield] )
When processing the production
PrimaryExpression[Yield]
: CoverParenthesizedExpressionAndArrowParameterList[?Yield]
the interpretation of CoverParenthesizedExpressionAndArrowParameterList is refined using the following grammar:
[
Elisionopt ]
[
ElementList[?Yield] ]
[
ElementList[?Yield] ,
Elisionopt ]
,
Elisionopt AssignmentExpression[In, ?Yield],
Elisionopt SpreadElement[?Yield]{
}
{
PropertyDefinitionList[?Yield] }
{
PropertyDefinitionList[?Yield] ,
}
,
PropertyDefinition[?Yield]:
AssignmentExpression[In, ?Yield][
Expression[In, ?Yield] ]
.
IdentifierNamenew
MemberExpression[?Yield] Arguments[?Yield][
Expression[In, ?Yield] ]
.
IdentifierName...
AssignmentExpression[In, ?Yield],
AssignmentExpression[In, ?Yield],
...
AssignmentExpression[In, ?Yield]++
--
delete
UnaryExpression[?Yield]void
UnaryExpression[?Yield]typeof
UnaryExpression[?Yield]++
UnaryExpression[?Yield]--
UnaryExpression[?Yield]+
UnaryExpression[?Yield]-
UnaryExpression[?Yield]~
UnaryExpression[?Yield]!
UnaryExpression[?Yield]+
MultiplicativeExpression[?Yield]-
MultiplicativeExpression[?Yield]<<
AdditiveExpression[?Yield]>>
AdditiveExpression[?Yield]>>>
AdditiveExpression[?Yield]<
ShiftExpression[?Yield]>
ShiftExpression[?Yield]<=
ShiftExpression[? Yield]>=
ShiftExpression[?Yield]instanceof
ShiftExpression[?Yield]in
ShiftExpression[?Yield]==
RelationalExpression[?In, ?Yield]!=
RelationalExpression[?In, ?Yield]===
RelationalExpression[?In, ?Yield]!==
RelationalExpression[?In, ?Yield]&
EqualityExpression[?In, ?Yield]^
BitwiseANDExpression[?In, ?Yield]|
BitwiseXORExpression[?In, ?Yield]&&
BitwiseORExpression[?In, ?Yield]||
LogicalANDExpression[?In, ?Yield]?
AssignmentExpression[In, ?Yield] :
AssignmentExpression[?In, ?Yield]=
AssignmentExpression[?In, ?Yield],
AssignmentExpression[?In, ?Yield],
LexicalBinding[?In, ?Yield],
VariableDeclaration[?In, ?Yield]{
}
{
BindingPropertyList[?Yield] }
{
BindingPropertyList[?Yield] ,
}
[
Elisionopt BindingRestElement[?Yield]opt ]
[
BindingElementList[?Yield] ]
[
BindingElementList[?Yield] ,
Elisionopt BindingRestElement[?Yield]opt ]
,
BindingProperty[?Yield],
BindingElisionElement[?Yield]:
BindingElement[?Yield]{
, function
, class
, let [
}] Expression[In, ?Yield] ;
if
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return] else
Statement[?Yield, ?Return]if
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return]do
Statement[?Yield, ?Return] while
(
Expression[In, ?Yield] )
;
while
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
[lookahead ∉ {let [
}] Expression[?Yield]opt ;
Expression[In, ?Yield]opt ;
Expression[In, ?Yield]opt )
Statement[?Yield, ?Return]for
(
var
VariableDeclarationList[?Yield] ;
Expression[In, ?Yield]opt ;
Expression[In, ?Yield]opt )
Statement[?Yield, ?Return]for
(
LexicalDeclaration[?Yield] Expression[In, ?Yield]opt ;
Expression[In, ?Yield]opt )
Statement[?Yield, ?Return]for
(
[lookahead ∉ {let [
}] LeftHandSideExpression[?Yield] in
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
var
ForBinding[?Yield] in
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
ForDeclaration[?Yield] in
Expression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
[lookahead ≠ let ] LeftHandSideExpression[?Yield] of
AssignmentExpression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
var
ForBinding[?Yield] of
AssignmentExpression[In, ?Yield] )
Statement[?Yield, ?Return]for
(
ForDeclaration[?Yield] of
AssignmentExpression[In, ?Yield] )
Statement[?Yield, ?Return]continue
;
continue
[no LineTerminator here] LabelIdentifier[?Yield] ;
return
;
return
[no LineTerminator here] Expression[In, ?Yield] ;
switch
(
Expression[In, ?Yield] )
CaseBlock[?Yield, ?Return]{
CaseClauses[?Yield, ?Return]opt }
{
CaseClauses[?Yield, ?Return]opt DefaultClause[?Yield, ?Return] CaseClauses[?Yield, ?Return]opt }
case
Expression[In, ?Yield] :
StatementList[?Yield, ?Return]opt:
LabelledItem[?Yield, ?Return]try
Block[?Yield, ?Return] Catch[?Yield, ?Return]try
Block[?Yield, ?Return] Finally[?Yield, ?Return]try
Block[?Yield, ?Return] Catch[?Yield, ?Return] Finally[?Yield, ?Return]function
BindingIdentifier[?Yield] (
FormalParameters )
{
FunctionBody }
function
(
FormalParameters )
{
FunctionBody }
,
FunctionRestParameter[?Yield]=>
ConciseBody[?In]When the production
ArrowParameters[Yield]
: CoverParenthesizedExpressionAndArrowParameterList[?Yield]
is recognized the following grammar is used to refine the interpretation of CoverParenthesizedExpressionAndArrowParameterList :
(
StrictFormalParameters )
{
FunctionBody }
get
PropertyName[?Yield] (
)
{
FunctionBody }
set
PropertyName[?Yield] (
PropertySetParameterList )
{
FunctionBody }
*
PropertyName[?Yield] (
StrictFormalParameters[Yield] )
{
GeneratorBody }
function
*
BindingIdentifier[?Yield] (
FormalParameters[Yield] )
{
GeneratorBody }
function
*
(
FormalParameters[Yield] )
{
GeneratorBody }
function
*
BindingIdentifier[Yield]opt (
FormalParameters[Yield] )
{
GeneratorBody }
yield
yield
[no LineTerminator here] AssignmentExpression[?In, Yield]yield
[no LineTerminator here] *
AssignmentExpression[?In, Yield]class
BindingIdentifier[?Yield] ClassTail[?Yield]class
ClassTail[?Yield],
NameSpaceImport,
NamedImportsexport
*
FromClause ;
export
ExportClause FromClause ;
export
ExportClause ;
export
VariableStatementexport
Declarationexport
default
HoistableDeclaration[Default]export
default
ClassDeclaration[Default]export
default
[lookahead ∉ {function
, class
}] AssignmentExpression[In] ;
+
StrUnsignedDecimalLiteral-
StrUnsignedDecimalLiteral.
DecimalDigitsopt ExponentPartopt.
DecimalDigits ExponentPartoptAll grammar symbols not explicitly defined by the StringNumericLiteral grammar have the definitions used in the Lexical Grammar for numeric literals (11.8.3)
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
*
+
?
{
DecimalDigits }
{
DecimalDigits ,
}
{
DecimalDigits ,
DecimalDigits }
.
\
AtomEscape[?U](
Disjunction[?U] )
(
?
:
Disjunction[?U] )
c
ControlLettera
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
u
LeadSurrogate \u
TrailSurrogateu
LeadSurrogateu
TrailSurrogateu
NonSurrogateu
Hex4Digitsu{
HexDigits }
Each \u
TrailSurrogate for which the choice of associated u
LeadSurrogate is ambiguous shall be associated with the nearest possible u
LeadSurrogate that would otherwise have no corresponding \u
TrailSurrogate.
/
-
ClassAtom[?U] ClassRanges[?U]-
ClassAtom[?U] ClassRanges[?U]The ECMAScript language syntax and semantics defined in this annex are required when the ECMAScript host is a web browser. The content of this annex is normative but optional if the ECMAScript host is not a web browser.
NOTE This annex describes various legacy features and other characteristics of web browser based ECMAScript implementations. All of the language features and behaviours specified in this annex have one or more undesirable characteristics and in the absence of legacy usage would be removed from this specification. However, the usage of these features by large numbers of existing web pages means that web browsers must continue to support them. The specifications in this annex defined the requirements for interoperable implementations of these legacy features.
These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code. ECMAScript implementations are discouraged from implementing these features unless the implementation is part of a web browser or is required to run the same legacy ECMAScript code that web browsers encounter.
The syntax and semantics of 11.8.3 is extended as follows except that this extension is not allowed for strict mode code:
0
OctalDigit0
0
NonOctalDigit0
OctalDigit8
9
B.1.1.1 Static Semantics
The MV of LegacyOctalIntegerLiteral :: 0
OctalDigit is the MV of OctalDigit.
The MV of LegacyOctalIntegerLiteral :: LegacyOctalIntegerLiteral OctalDigit is (the MV of LegacyOctalIntegerLiteral times 8) plus the MV of OctalDigit.
The MV of DecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral is the MV of NonOctalDecimalIntegerLiteral.
The MV of NonOctalDecimalIntegerLiteral :: 0
NonOctalDigit is the MV of NonOctalDigit.
The MV of NonOctalDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral NonOctalDigit is (the MV of LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV of NonOctalDigit.
The MV of NonOctalDecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral DecimalDigit is (the MV of NonOctalDecimalIntegerLiteral times 10) plus the MV of DecimalDigit.
The MV of LegacyOctalLikeDecimalIntegerLiteral ::
0
OctalDigit is the MV of OctalDigit.
The MV of LegacyOctalLikeDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral OctalDigit is (the MV of LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV of OctalDigit.
The MV of NonOctalDigit :: 8
is 8.
The MV of NonOctalDigit :: 9
is 9.
The syntax and semantics of 11.8.4 is extended as follows except that this extension is not allowed for strict mode code:
0
1
2
3
4
5
6
7
This definition of EscapeSequence is not used in strict mode or when parsing TemplateCharacter (11.8.6).
B.1.2.1 Static Semantics
0
is 0.1
is 1.2
is 2.3
is 3.4
is 4.5
is 5.6
is 6.7
is 7.The syntax and semantics of 11.4 is extended as follows except that this extension is not allowed when parsing source code using the goal symbol Module :
/*
FirstCommentLineopt LineTerminator MultiLineCommentCharsopt */
HTMLCloseCommentopt<!--
SingleLineCommentCharsopt/*
SingleLineDelimitedCommentCharsopt */
-->
SingleLineCommentCharsopt*
SingleLinePostAsteriskCommentCharsopt*
or LineTerminator*
SingleLinePostAsteriskCommentCharsopt/
or *
or LineTerminatorSimilar to a MultiLineComment that contains a line terminator code point, a SingleLineHTMLCloseComment is considered to be a LineTerminator for purposes of parsing by the syntactic grammar.
The syntax of 21.2.1 is modified and extended as follows. These changes introduce ambiguities that are broken by the ordering of grammar productions and by contextual information. When parsing using the following grammar, each alternative is considered only if previous production alternatives do not match.
This alternative pattern grammar and semantics only changes the syntax and semantics of BMP patterns. The following grammar extensions include productions parameterized with the [U] parameter. However, none of these extensions change the syntax of Unicode patterns recognized when parsing with the [U] parameter present on the goal symbol.
Syntax
.
\
AtomEscape(
Disjunction )
(
?
:
Disjunction )
.
\
AtomEscape[?U](
Disjunction[?U] )
(
?
:
Disjunction[?U] )
^
$
\
.
*
+
?
(
)
[
]
{
}
|
^
$
\
.
*
+
?
(
)
[
]
|
(
?
=
Disjunction )
(
?
!
Disjunction )
^
$
\
b
\
B
(
?
=
Disjunction[U] )
(
?
!
Disjunction[U] )
but
only
if
the
integer
value
of
DecimalEscape is
<=
NCapturingParensc
ControlLetter/
c
-
ClassAtom[U] ClassRanges[U]-
ClassAtomInRange ClassRanges-
ClassAtom[U] ClassRanges[U]-
ClassAtomInRange ClassRanges-
\
or ]
or -
\
ClassEscape[?U]-
\
or ]
or -
\
ClassEscape but
only
if
ClassEscape evaluates
to
a
CharSet with
exactly
one
character
\
IdentityEscapeb
NOTE When the same left hand sides occurs with both [+U] and [~U] guards it is to control the disambiguation priority.
B.1.4.1 Pattern Semantics
The semantics of 21.2.2 is extended as follows:
Within 21.2.2.5 reference to “Atom :: (
Disjunction )
”
are to be interpreted as meaning “Atom :: (
Disjunction )
” or “AtomNoBrace :: (
Disjunction )
”.
Term (21.2.2.5) includes the following additional evaluation rule:
The production Term :: QuantifiableAssertion Quantifier evaluates the same as the production Term :: Atom Quantifier but with QuantifiableAssertion substituted for Atom.
Atom (21.2.2.8) evaluation rules for the Atom productions except for Atom :: PatternCharacter are also used for the AtomNoBrace productions, but with AtomNoBrace substituted for Atom. The following evaluation rule is also added:
The production AtomNoBrace :: PatternCharacterNoBrace evaluates as follows:
CharacterEscape (21.2.2.10) includes the following additional evaluation rule:
The production CharacterEscape :: LegacyOctalEscapeSequence evaluates by evaluating the SV of the LegacyOctalEscapeSequence (see B.1.2) and returning its character result.
ClassAtom (21.2.2.17) includes the following additional evaluation rules:
The production ClassAtomInRange :: -
evaluates by returning the CharSet containing the one character -
.
The production ClassAtomInRange :: ClassAtomNoDashInRange evaluates by evaluating ClassAtomNoDashInRange to obtain a CharSet and returning that CharSet.
ClassAtomNoDash (21.2.2.18) includes the following additional evaluation rules:
The production ClassAtomNoDashInRange :: SourceCharacter but not one of \
or ]
or -
evaluates
by returning a one-element CharSet containing the character represented by SourceCharacter.
The production ClassAtomNoDashInRange :: \
ClassEscape but only if…, evaluates by evaluating ClassEscape to obtain a CharSet and returning that CharSet.
The production ClassAtomNoDashInRange :: \
IdentityEscape evaluates by returning the character represented by IdentityEscape.
When the ECMAScript host is a web browser the following additional properties of the standard built-in objects are defined.
The escape
function is a property of the global object. It computes a new version of a String value in
which certain code units have been replaced by a hexadecimal escape sequence.
For those code units being replaced whose value is 0x00FF
or less, a two-digit escape sequence of the form
%
xx is used. For those characters being replaced whose code unit value is greater than
0x00FF
, a four-digit escape sequence of the form %u
xxxx is used.
The escape
function is the %escape% intrinsic object. When the escape
function is called with one argument string, the following steps are taken:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@*_+-./
", then
%u
wxyz" where
wxyz are the code units of the four hexadecimal digits encoding the value of char.%
xy" where xy
are the code units of two hexadecimal digits encoding the value of char.NOTE The encoding is partly based on the encoding described in RFC 1738, but the entire encoding specified in this standard is described above without regard to the contents of RFC 1738. This encoding does not reflect changes to RFC 1738 made by RFC 3986.
The unescape
function is a property of the global object. It computes a new version of a String value in
which each escape sequence of the sort that might be introduced by the escape
function is replaced with the
code unit that it represents.
The unescape
function is the %unescape% intrinsic object. When the
unescape
function is called with one argument string, the following steps are taken:
%
,
u
and the four code units at indices k+2, k+3, k+4, and k+5 within
string are all hexadecimal digits, then
Object.prototype.__proto__ is an accessor property with attributes { [[Enumerable]]: false, [[Configurable]]: true }. The [[Get]] and [[Set]] attributes are defined as follows
The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps:
The value of the [[Set]] attribute is a built-in function that takes an argument proto. It performs the following steps:
The substr
method takes two arguments, start and length, and
returns a substring of the result of converting the this object to a String, starting from index start
and running for length code units (or through the end of the String if length is undefined).
If start is negative, it is treated as (sourceLength+start) where sourceLength is the length of the String. The result is
a String value, not a String object. The following steps are taken:
""
.The length
property of the substr
method is 2.
NOTE The substr
function is intentionally generic; it does not require that its
this value be a String object. Therefore it can be transferred to other kinds of objects for use as a method.
When the anchor method is called with argument name, the following steps are taken:
"a"
, "name"
,
name).The abstract operation CreateHTML is called with arguments string, tag, attribute, and value. The arguments tag and attribute must be String values. The following steps are taken:
"<"
and tag."""
.">"
."</"
, tag, and
">"
.When the big method is called with no arguments, the following steps are taken:
"big"
, ""
,
""
).When the blink method is called with no arguments, the following steps are taken:
"blink"
, ""
,
""
).When the bold method is called with no arguments, the following steps are taken:
"b"
, ""
, ""
).When the fixed method is called with no arguments, the following steps are taken:
"tt"
, ""
, ""
).When the fontcolor method is called with argument color, the following steps are taken:
"font"
, "color"
,
color).When the fontsize method is called with argument size, the following steps are taken:
"font"
, "size"
,
size).When the italics method is called with no arguments, the following steps are taken:
"i"
, ""
, ""
).When the link method is called with argument url, the following steps are taken:
"a"
, "href"
, url).When the small method is called with no arguments, the following steps are taken:
"small"
, ""
,
""
).When the strike method is called with no arguments, the following steps are taken:
"strike"
, ""
,
""
).When the sub method is called with no arguments, the following steps are taken:
"sub"
, ""
,
""
).When the sup method is called with no arguments, the following steps are taken:
"sup"
, ""
,
""
).NOTE The getFullYear
method is preferred for nearly all purposes, because it
avoids the “year 2000 problem.”
When the getYear method is called with no arguments, the following steps are taken:
NOTE The setFullYear
method is preferred for nearly all purposes, because it
avoids the “year 2000 problem.”
When the setYear method is called with one argument year, the following steps are taken:
NOTE The property toUTCString
is preferred. The toGMTString
property is provided principally for compatibility with old code. It is recommended that the toUTCString
property be used in new ECMAScript code.
The function object that is the initial value of Date.prototype.toGMTString
is the same function object
that is the initial value of Date.prototype.toUTCString
.
When the compile method is called with arguments pattern and flags, the following steps are taken:
NOTE The compile
method completely reinitializes the this object RegExp
with a new pattern and flags. An implementation may interpret use of this method as an assertion that the resulting
RegExp object will be used multiple times and hence is a candidate for extra optimization.
The following Early Error rule is added to those in 12.2.6.1:
ObjectLiteral : {
PropertyDefinitionList }ObjectLiteral
:
{
PropertyDefinitionList ,
}
It is a Syntax Error if PropertyNameList of PropertyDefinitionList contains any duplicate entries for "__proto__"
and at least two of
those entries were obtained from productions of the form PropertyDefinition
: PropertyName :
AssignmentExpression .
NOTE The List returned by PropertyNameList does not include string literal property names defined as using a ComputedPropertyName.
In 12.2.6.9 the
PropertyDefinitionEvaluation algorithm for the production
PropertyDefinition
: PropertyName :
AssignmentExpression
is replaced with the following definition:
:
AssignmentExpression"__proto__"
and if IsComputedPropertyKey(propKey) is
false, then
"name"
).Prior to ECMAScript 2015, the specification of LabelledStatement did not allow for the association of a statement label with a FunctionDeclaration. However, a labelled FunctionDeclaration was an allowable extension for non-strict code and most browser-hosted ECMAScript implementations supported that extension. In ECMAScript 2015, the grammar productions for LabelledStatement permits use of FunctionDeclaration as a LabelledItem but 13.13.1 includes an Early Error rule that produces a Syntax Error if that occurs. For web browser compatibility, that rule is modified with the addition of the underlined text:
Prior to ECMAScript 2015, the ECMAScript specification did not define the occurrence of a FunctionDeclaration as an element of a Block statement’s StatementList. However, support for that form of FunctionDeclaration was an allowable extension and most browser-hosted ECMAScript implementations permitted them. Unfortunately, the semantics of such declarations differ among those implementations. Because of these semantic differences, existing web ECMAScript code that uses Block level function declarations is only portable among browser implementation if the usage only depends upon the semantic intersection of all of the browser implementations for such declarations. The following are the use cases that fall within that intersection semantics:
A FunctionDeclaration whose BindingIdentifier is the name f occurs exactly once within the function code of an enclosing function g and that declaration is nested within a Block.
No other declaration of f that is not a var
declaration occurs within the function code
of g
All occurrences of f as an IdentifierReference are within the StatementList of the Block containing the declaration of f.
A FunctionDeclaration whose BindingIdentifier is the name f occurs exactly once within the function code of an enclosing function g and that declaration is nested within a Block.
No other declaration of f that is not a var
declaration occurs within the function code
of g
There may be occurrences of f as an IdentifierReference within the StatementList of the Block containing the declaration of f.
There is at least one occurrence of f as an IdentifierReference within the function code of g that lexically follows the Block containing the declaration of f.
A FunctionDeclaration whose BindingIdentifier is the name f occurs exactly once within the function code of an enclosing function g and that declaration is nested within a Block.
No other declaration of f that is not a var
declaration occurs within the function code
of g
There may be occurrences of f as an IdentifierReference within the StatementList of the Block containing the declaration of f.
There is at least one occurrence of f as an IdentifierReference within another function h that is nested within g and no other declaration of f shadows the references to f from within h.
All invocations of h occur after the declaration of f has been evaluated.
The first use case is interoperable with the semantics of Block level function declarations provided by ECMAScript 2015. Any pre-existing ECMAScript code that employees that use case will operate using the Block level function declarations semantics defined by clauses 9, 13, and 14 of this specification.
ECMAScript 2015 interoperability for the second and third use cases requires the following extensions to the clause 9 and clause 14 semantics. During FunctionDeclarationInstantiation (9.2.12) the following steps are performed in place of step 29:
If an ECMAScript implementation has a mechanism for reporting diagnostic warning messages, a warning should be produced for each function whose function code contains a FunctionDeclaration for which steps 1.a.ii.1-3 will be performed.
The following rules for IfStatement augment those in 13.6:
if
(
Expression[In, ?Yield] )
FunctionDeclaration[?Yield] else
Statement[?Yield, ?Return]if
(
Expression[In, ?Yield] )
Statement[?Yield, ?Return] else
FunctionDeclaration[?Yield]if
(
Expression[In, ?Yield] )
FunctionDeclaration[?Yield] else
FunctionDeclaration[?Yield]if
(
Expression[In, ?Yield] )
FunctionDeclaration[?Yield]The above rules are only applied when parsing code that is not strict mode code. If any such code is match by one of these rules subsequent processing of that code takes places as if each matching occurrence of FunctionDeclaration[?Yield] was the sole StatementListItem of a BlockStatement occupying that position in the source code. The semantics of such a synthetic BlockStatement includes the web legacy compatibility semantics specified in B.3.3.
The content of subclause 13.15.1 is replaced with the following:
catch
(
CatchParameter )
BlockIt is a Syntax Error if BoundNames of CatchParameter contains any duplicate elements.
It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the LexicallyDeclaredNames of Block.
It is a Syntax Error if any element of the BoundNames of CatchParameter also occurs in the VarDeclaredNames of Block, unless that element is only bound by a VariableStatement or the VariableDeclarationList of a for statement, or the ForBinding of a for-in statement.
NOTE The Block of a Catch clause may contain
var
declarations that bind a name that is also bound by the CatchParameter. At
runtime, such bindings are instantiated in the VariableDeclarationEnvironment. They do not shadow the same-named bindings
introduced by the CatchParameter and hence the Initializer for such
var
declarations will assign to the corresponding catch parameter rather than the var
binding.
The relaxation of the normal static semantic rule does not apply to names only bound by for-of statements.
This modified behaviour also applies to var
and function
declarations introduced by direct
evals contained within the Block of a Catch clause. This change is
accomplished by modify the algorithm of 18.2.1.2 as follows:
Step 5.d.ii.2.a.i is replaced by:
i. If thisEnvRec is not the Environment Record for a Catch clause, throw a SyntaxError exception.
ii. If name is bound by any syntactic form other than a FunctionDeclaration, a VariableStatement, the VariableDeclarationList of a for statement, or the ForBinding of a for-in statement, throw a SyntaxError exception.
The strict mode restriction and exceptions
implements
, interface
, let
, package
, private
,
protected
, public
, static
, and yield
are reserved words within strict mode code. (11.6.2).
A conforming implementation, when processing strict mode code, may not extend the syntax of NumericLiteral (11.8.3) to include LegacyOctalIntegerLiteral as described in B.1.1.
A conforming implementation, when processing strict mode code, may not extend the syntax of EscapeSequence to include LegacyOctalEscapeSequence as described in B.1.2.
Assignment to an undeclared identifier or otherwise unresolvable reference does not create a property in the global
object. When a simple assignment occurs within strict mode code, its LeftHandSide
must not evaluate to an unresolvable Reference. If it does a
ReferenceError exception is thrown (6.2.3.2). The LeftHandSide also may not be a
reference to a data property with the attribute value {[[Writable]]:false}, to an accessor property with the
attribute value {[[Set]]:undefined}, nor to a non-existent property of an object whose [[Extensible]] internal slot has the value false. In these cases a
TypeError
exception is thrown (12.14).
The identifier eval
or arguments
may not appear as the LeftHandSideExpression of an
Assignment operator (12.14) or of a PostfixExpression (12.4) or as the UnaryExpression operated upon by a Prefix Increment (12.5.7) or a Prefix Decrement (12.5.8) operator.
Arguments objects for strict mode functions define non-configurable accessor properties named "caller"
and
"callee"
which throw a TypeError exception on access (9.2.7).
Arguments objects for strict mode functions do not dynamically share their array indexed property values with the corresponding formal parameter bindings of their functions. (9.4.4).
For strict mode functions, if an arguments object is created the binding of the local identifier arguments
to the arguments object is immutable and hence may not be the target of an assignment expression. (9.2.12).
It is a SyntaxError if the IdentifierName eval
or the IdentifierName
arguments
occurs as a BindingIdentifier within strict
mode code (12.1.1).
Strict mode eval code cannot instantiate variables or functions in the variable environment of the caller to eval. Instead, a new variable environment is created and that environment is used for declaration binding instantiation for the eval code (18.2.1).
If this is evaluated within strict mode code, then the this value is
not coerced to an object. A this value of null or undefined is not converted to the global object and
primitive values are not converted to wrapper objects. The this value passed via a function call (including calls
made using Function.prototype.apply
and Function.prototype.call
) do not coerce the passed this value to an object (9.2.1.2, 19.2.3.1, 19.2.3.3).
When a delete
operator occurs within strict mode code, a
SyntaxError is thrown if its UnaryExpression is a direct reference to a variable, function argument, or
function name (12.5.4.1).
When a delete
operator occurs within strict mode code, a
TypeError is thrown if the property to be deleted has the attribute { [[Configurable]]:false } (12.5.4.2).
Strict mode code may not include a WithStatement. The occurrence of a WithStatement in such a context is a SyntaxError (13.11.1).
It is a SyntaxError if a TryStatement with a Catch occurs within strict mode code and the Identifier of the Catch production is
eval
or arguments
(13.15.1).
It is a SyntaxError if the same BindingIdentifier appears more than once in the FormalParameters of a strict mode function. An attempt to create such a function using a
Function
or Generator
constructor is a SyntaxError (14.1.2, 19.2.1.1.1).
An implementation may not extend, beyond that defined in this specification, the meanings within strict mode functions of
properties named caller
or arguments
of function instances. ECMAScript code may not create or
modify properties with these names on function objects that correspond to strict mode functions (16.1).
8.1.1.4.15-8.1.1.4.18 Edition 5 and 5.1 used a property existence test to determine whether a global object property corresponding to a new global declaration already existed. ECMAScript 2015 uses an own property existence test. This corresponds to what has been most commonly implemented by web browsers.
9.4.2.1: The 5th Edition moved the capture of the current array length prior to the integer conversion of the array index or new length value. However, the captured length value could become invalid if the conversion process has the side-effect of changing the array length. ECMAScript 2015 specifies that the current array length must be captured after the possible occurrence of such side-effects.
20.3.1.15: Previous editions permitted the TimeClip abstract operation to return either +0 or −0 as the representation of a 0 time value. ECMAScript 2015 specifies that +0 always returned. This means that for ECMAScript 2015 the time value of a Date object is never observably −0 and methods that return time values never return −0.
20.3.1.16: If a time zone offset is not present, the local time zone is used.
Edition 5.1 incorrectly stated that a missing time zone should be interpreted as "z"
.
20.3.4.36: If the year cannot be represented using the Date Time String Format specified in 20.3.1.16 a RangeError exception is thrown. Previous editions did not specify the behaviour for that case.
20.3.4.41: Previous editions did not specify the value returned by Date.prototype.toString when this
time value is NaN. ECMAScript 2015 specifies the result to be the String value is "Invalid Date".
21.2.3.1, 21.2.3.2.4: Any LineTerminator code
points in the value of the source
property of an RegExp instance must be expressed using an escape sequence.
Edition 5.1 only required the escaping of "/"
.
21.2.5.6, 21.2.5.8: In previous
editions, the specifications for String.prototype.match
and String.prototype.replace
was incorrect for cases where the pattern argument was
a RegExp value whose global
is flag set. The previous specifications stated that for each attempt to match the
pattern, if lastIndex
did not change it should be incremented by 1. The correct behaviour is that
lastIndex
should be incremented by one only if the pattern matched the empty string.
22.1.3.24, 22.1.3.24.1: Previous editions did not
specify how a NaN value returned by a comparefn was interpreted by Array.prototype.sort
. ECMAScript 2015 specifies that such as value is treated as if
+0 was returned from the comparefn. ECMAScript 2015 also specifies that ToNumber is
applied to the result returned by a comparefn. In previous editions,
the effect of a comparefn result that is not a Number value was implementation dependent. In practice,
implementations call ToNumber.
7.1.3.1: In ECMAScript 2015, ToNumber applied to a String value now recognizes and converts BinaryIntegerLiteral and OctalIntegerLIteral numeric strings. In previous editions such strings were converted to NaN,
6.2.3: In ECMAScript 2015, Function calls are not allowed to return a Reference value.
11.6: In ECMAScript 2015, the valid code points for an IdentifierName are specified in terms of the Unicode properties “ID_Start” and “ID_Continue”. In previous editions, the valid IdentifierName or Identifier code points were specified by enumerating various Unicode code point categories.
11.9.1: In ECMAScript 2015, Automatic Semicolon Insertion adds a semicolon at the end of a do-while statement if the semicolon is missing. This change aligns the specification with the actual behaviour of most existing implementations.
12.2.6.1: In ECMAScript 2015, it is no longer an early error to have duplicate property names in Object Initializers.
12.14.1: In ECMAScript 2015, strict mode code containing an assignment to an immutable binding such as the function name of a FunctionExpression does not produce an early error. Instead it produces a runtime error.
13.5: In ECMAScript 2015, a StatementListItem beginning with
the token let
followed by the token [
is the start of a LexicalDeclaration. In
previous editions such a sequence would be the start of an ExpressionStatement.
13.6.7: In ECMAScript 2015, the normal completion value of an IfStatement is never the value empty. If no Statement part is evaluated or if the evaluated Statement part produces a normal completion whose value is empty, the completion value of the IfStatement is undefined.
13.7: In ECMAScript 2015, if the (
token of a for statement is
immediately followed by the token sequence let
[
then the let
is treated as the start of
a LexicalDeclaration. In previous editions such a token sequence would be the start of an Expression.
13.7: In ECMAScript 2015, if the ( token of a for-in statement is immediately
followed by the token sequence let
[
then the let
is treated as the start of a ForDeclaration. In previous editions such a token sequence would be the start of an LeftHandSideExpression.
13.7: Prior to ECMAScript 2015, an initialization expression could appear as part of
the VariableDeclaration that precedes the in
keyword. The value of that expression was always discarded. In
ECMAScript 2015, the ForBind in that same position does not allow the occurrence of such an initializer.
13.7: In ECMAScript 2015, the completion value of an IterationStatement is never the value empty. If the Statement part of an IterationStatement is not evaluated or if the final evaluation of the Statement part produces a completion whose value is empty, the completion value of the IterationStatement is undefined.
13.11.7: In ECMAScript 2015, the normal completion value of a WithStatement is never the value empty. If evaluation of the Statement part of a WithStatement produces a normal completion whose value is empty, the completion value of the WithStatement is undefined.
13.12.11: In ECMAScript 2015, the completion value of a SwitchStatement is never the value empty. If the CaseBlock part of a SwitchStatement produces a completion whose value is empty, the completion value of the SwitchStatement is undefined.
13.15: In ECMAScript 2015, it is an early error for a Catch clause
to contained a var
declaration for the same Identifier that appears as the Catch clause parameter. In previous editions, such a variable declaration would be instantiated in the
enclosing variable environment but the declaration’s Initializer value would be assigned to the
Catch parameter.
13.15, 18.2.1.2: In ECMAScript 2015, a
runtime SyntaxError is thrown if a Catch clause evaluates a non-strict direct
eval
whose eval code includes a var
or FunctionDeclaration
declaration that binds the
same Identifier that appears as the Catch clause parameter.
13.15.8: In ECMAScript 2015, the completion value of a TryStatement is never the value empty. If the Block part of a TryStatement evaluates to a normal completion whose value is empty, the completion value of the TryStatement is undefined. If the Block part of a TryStatement evaluates to a throw completion and it has a Catch part that evaluates to a normal completion whose value is empty, the completion value of the TryStatement is undefined if there is no Finally clause or if its Finally clause evalulates to an empty normal completion.
14.3.9 In ECMAScript 2015, the function
objects that are created as the values of the [[Get]] or [[Set]] attribute of accessor properties in an ObjectLiteral are not constructor functions and they do not have a prototype
own property. In the
previous edition, they were constructors and had a prototype
property.
19.1.2.5: In ECMAScript 2015, if the argument to Object.freeze
is not an object it is treated as if it was a non-extensible ordinary object
with no own properties. In the previous edition, a non-object argument always causes a TypeError to
be thrown.
19.1.2.6: In ECMAScript 2015, if the argument to Object.getOwnPropertyDescriptor
is not an object an attempt is made to
coerce the argument using ToObject. If the coercion is successful the result is used in place of the
original argument value. In the previous edition, a non-object argument always causes a TypeError to
be thrown.
19.1.2.7: In ECMAScript 2015, if the argument to Object.getOwnPropertyNames
is not an object an attempt is made to coerce the
argument using ToObject. If the coercion is successful the result is used in place of the original
argument value. In the previous edition, a non-object argument always causes a TypeError to be
thrown.
19.1.2.9: In ECMAScript 2015, if the argument to Object.getPrototypeOf
is not an object an attempt is made to coerce the argument
using ToObject. If the coercion is successful the result is used in place of the original argument
value. In the previous edition, a non-object argument always causes a TypeError to be thrown.
19.1.2.11: In ECMAScript 2015, if the argument to Object.isExtensible
is not an object it is treated as if it was a non-extensible
ordinary object with no own properties. In the previous edition, a non-object argument always causes a TypeError to be thrown.
19.1.2.12: In ECMAScript 2015, if the argument to Object.isFrozen
is not an object it is treated as if it was a non-extensible ordinary
object with no own properties. In the previous edition, a non-object argument always causes a TypeError to be thrown.
19.1.2.13: In ECMAScript 2015, if the argument to Object.isSealed
is not an object it is treated as if it was a non-extensible ordinary
object with no own properties. In the previous edition, a non-object argument always causes a TypeError to be thrown.
19.1.2.14: In ECMAScript 2015, if the argument to Object.keys
is not an object an attempt is made to coerce the argument using ToObject. If the coercion is successful the result is used in place of the original argument value. In
the previous edition, a non-object argument always causes a TypeError to be thrown.
19.1.2.15: In ECMAScript 2015, if the argument to Object.preventExtensions
is not an object it is treated as if it was a
non-extensible ordinary object with no own properties. In the previous edition, a non-object argument always causes a TypeError to be thrown.
19.1.2.17: In ECMAScript 2015, if the argument to Object.seal
is not an object it is treated as if it was a non-extensible ordinary object with
no own properties. In the previous edition, a non-object argument always causes a TypeError to be
thrown.
19.2.3.2: In ECMAScript 2015, the [[Prototype]] internal slot of a bound function is set to the [[GetPrototypeOf]] value of its target function. In the previous edition, [[Prototype]] was always set to %FunctionPrototype%.
19.2.4.1: In ECMAScript 2015, the length
property of function
instances is configurable. In previous editions it was non-configurable.
19.3.3: In ECMAScript 2015, the Boolean prototype object is not a Boolean instance. In previous editions it was a Boolean instance whose Boolean value was false.
19.5.6.2: In ECMAScript 2015, the [[Prototype]] internal slot of a NativeError constructor is the Error constructor. In previous editions it was the Function prototype object.
20.1.3 In ECMAScript 2015, the Number prototype object is not a Number instance. In previous editions it was a Number instance whose number value was +0.
20.3.4 In ECMAScript 2015, the Date prototype object is not a Date instance. In previous editions it was a Date instance whose TimeValue was NaN.
21.1.3.10 In ECMAScript 2015, the String.prototype.localeCompare
function must treat Strings that are
canonically equivalent according to the Unicode standard as being identical. In previous editions implementations were permitted
to ignore canonical equivalence and could instead use a bit-wise comparison.
21.1.3 In ECMAScript 2015, the String prototype object is not a String instance. In previous editions it was a String instance whose String value was the empty string.
21.1.3.22 and 21.1.3.24 In ECMAScript 2015, lowercase/upper conversion processing operates on code points. In previous editions such the conversion processing was only applied to individual code units. The only affected code points are those in the Deseret block of Unicode
21.1.3.25 In ECMAScript 2015, the String.prototype.trim
method is defined to recognize white space code points that
may exists outside of the Unicode BMP. However, as of Unicode 7 no such code points are defined. In previous editions such code
points would not have been recognized as white space.
21.2.3.1 In ECMAScript 2015, If the pattern argument is a RegExp instance and the flags argument is not undefined, a new RegExp instance is created just like pattern except that pattern’s flags are replaced by the argument flags. In previous editions a TypeError exception was thrown when pattern was a RegExp instance and flags was not undefined.
21.2.5 In ECMAScript 2015, the RegExp prototype object is not a RegExp instance. In previous editions it was a RegExp instance whose pattern is the empty string.
21.2.5 In ECMAScript 2015, source
,
global
, ignoreCase
, and multiline
are accessor properties defined on the RegExp prototype
object. In previous editions they were data properties defined on RegExp instances
[1] IEEE Std 754-2008: IEEE Standard for Floating-Point Arithmetic. Institute of Electrical and Electronic Engineers, New York (2008)
[2] The Unicode Standard, Version 5.0, as amended by Unicode 5.1.0, or
successor.
<http://www.unicode.org/versions/latest>
[3] Unicode Standard Annex #15, Unicode Normalization Forms, version Unicode 5.1.0, or
successor.
<http://www.unicode.org/reports/tr15/>
[4] Unicode Standard Annex #31, Unicode Identifiers and Pattern Syntax, version Unicode 5.1.0, or successor. <http://www.unicode.org/reports/tr31/>
[5] Unicode Technical Note #5: Canonical Equivalence in Applications, available at <http://www.unicode.org/notes/tn5/>
[6] Unicode Technical Standard #10: Unicode Collation Algorithm version 5.1.0, or successor, available at <http://www.unicode.org/reports/tr10/>
[7] IANA Time Zone Database at <http://www.iana.org/time-zones>
[8] ISO 8601:2004(E) Data elements and interchange formats – Information interchange — Representation of dates and times
[9] RFC 1738 “Uniform Resource Locators (URL)”, available at <http://tools.ietf.org/html/rfc1738>
[10] RFC 2396 “Uniform Resource Identifiers (URI): Generic Syntax”, available at <http://tools.ietf.org/html/rfc2396>
[11] RFC 3629 “UTF-8, a transformation format of ISO 10646”, available at <http://tools.ietf.org/html/rfc3629>