Table of contents
scripts
Select CLI Version:
Table of contents
Description
The "scripts"
property of your package.json
file supports a number of built-in scripts and their preset life cycle events as well as arbitrary scripts. These all can be executed by running npm run-script <stage>
or npm run <stage>
for short. Pre and post commands with matching names will be run for those as well (e.g. premyscript
, myscript
, postmyscript
). Scripts from dependencies can be run with npm explore <pkg> -- npm run <stage>
.
Pre & Post Scripts
To create "pre" or "post" scripts for any scripts defined in the "scripts"
section of the package.json
, simply create another script with a matching name and add "pre" or "post" to the beginning of them.
{"scripts": {"precompress": "{{ executes BEFORE the `compress` script }}","compress": "{{ run command to compress files }}","postcompress": "{{ executes AFTER `compress` script }}"}}
In this example npm run compress
would execute these scripts as described.
Life Cycle Scripts
There are some special life cycle scripts that happen only in certain situations. These scripts happen in addition to the pre<event>
, post<event>
, and <event>
scripts.
prepare
,prepublish
,prepublishOnly
,prepack
,postpack
prepare (since [email protected]
)
-
Runs any time before the package is packed, i.e. during
npm publish
andnpm pack
-
Runs BEFORE the package is packed
-
Runs BEFORE the package is published
-
Runs on local
npm install
without any arguments -
Run AFTER
prepublish
, but BEFOREprepublishOnly
-
NOTE: If a package being installed through git contains a
prepare
script, itsdependencies
anddevDependencies
will be installed, and the prepare script will be run, before the package is packaged and installed. -
As of
npm@7
these scripts run in the background. To see the output, run with:--foreground-scripts
.
prepublish (DEPRECATED)
- Does not run during
npm publish
, but does run duringnpm ci
andnpm install
. See below for more info.
prepublishOnly
- Runs BEFORE the package is prepared and packed, ONLY on
npm publish
.
prepack
- Runs BEFORE a tarball is packed (on "
npm pack
", "npm publish
", and when installing a git dependencies). - NOTE: "
npm run pack
" is NOT the same as "npm pack
". "npm run pack
" is an arbitrary user defined script name, where as, "npm pack
" is a CLI defined command.
postpack
- Runs AFTER the tarball has been generated but before it is moved to its final destination (if at all, publish does not save the tarball locally)
Prepare and Prepublish
Deprecation Note: prepublish
Since [email protected]
, the npm CLI has run the prepublish
script for both npm publish
and npm install
, because it's a convenient way to prepare a package for use (some common use cases are described in the section below). It has also turned out to be, in practice, very confusing. As of [email protected]
, a new event has been introduced, prepare
, that preserves this existing behavior. A new event, prepublishOnly
has been added as a transitional strategy to allow users to avoid the confusing behavior of existing npm versions and only run on npm publish
(for instance, running the tests one last time to ensure they're in good shape).
See https://github.com/npm/npm/issues/10074 for a much lengthier justification, with further reading, for this change.
Use Cases
If you need to perform operations on your package before it is used, in a way that is not dependent on the operating system or architecture of the target system, use a prepublish
script. This includes tasks such as:
- Compiling CoffeeScript source code into JavaScript.
- Creating minified versions of JavaScript source code.
- Fetching remote resources that your package will use.
The advantage of doing these things at prepublish
time is that they can be done once, in a single place, thus reducing complexity and variability. Additionally, this means that:
- You can depend on
coffee-script
as adevDependency
, and thus your users don't need to have it installed. - You don't need to include minifiers in your package, reducing the size for your users.
- You don't need to rely on your users having
curl
orwget
or other system tools on the target machines.
Life Cycle Operation Order
npm cache add
prepare
npm ci
preinstall
install
postinstall
prepublish
preprepare
prepare
postprepare
These all run after the actual installation of modules into node_modules
, in order, with no internal actions happening in between
npm diff
prepare
npm install
These also run when you run npm install -g <pkg-name>
preinstall
install
postinstall
prepublish
preprepare
prepare
postprepare
If there is a binding.gyp
file in the root of your package and you haven't defined your own install
or preinstall
scripts, npm will default the install
command to compile using node-gyp via node-gyp rebuild
These are run from the scripts of <pkg-name>
npm pack
prepack
prepare
postpack
npm publish
prepublishOnly
prepack
prepare
postpack
publish
postpublish
prepare
will not run during --dry-run
npm rebuild
preinstall
install
postinstall
prepare
prepare
is only run if the current directory is a symlink (e.g. with linked packages)
npm restart
If there is a restart
script defined, these events are run, otherwise stop
and start
are both run if present, including their pre
and post
iterations)
prerestart
restart
postrestart
npm run <user defined>
pre<user-defined>
<user-defined>
post<user-defined>
npm start
prestart
start
poststart
If there is a server.js
file in the root of your package, then npm will default the start
command to node server.js
. prestart
and poststart
will still run in this case.
npm stop
prestop
stop
poststop
npm test
pretest
test
posttest
A Note on a lack of npm uninstall
scripts
While npm v6 had uninstall
lifecycle scripts, npm v7 does not. Removal of a package can happen for a wide variety of reasons, and there's no clear way to currently give the script enough context to be useful.
Reasons for a package removal include:
- a user directly uninstalled this package
- a user uninstalled a dependant package and so this dependency is being uninstalled
- a user uninstalled a dependant package but another package also depends on this version
- this version has been merged as a duplicate with another version
- etc.
Due to the lack of necessary context, uninstall
lifecycle scripts are not implemented and will not function.
User
When npm is run as root, scripts are always run with the effective uid and gid of the working directory owner.
Environment
Package scripts run in an environment where many pieces of information are made available regarding the setup of npm and the current state of the process.
path
If you depend on modules that define executable scripts, like test suites, then those executables will be added to the PATH
for executing the scripts. So, if your package.json has this:
{"name": "foo","dependencies": {"bar": "0.1.x"},"scripts": {"start": "bar ./test"}}
then you could run npm start
to execute the bar
script, which is exported into the node_modules/.bin
directory on npm install
.
package.json vars
The package.json fields are tacked onto the npm_package_
prefix. So, for instance, if you had {"name":"foo", "version":"1.2.5"}
in your package.json file, then your package scripts would have the npm_package_name
environment variable set to "foo", and the npm_package_version
set to "1.2.5". You can access these variables in your code with process.env.npm_package_name
and process.env.npm_package_version
, and so on for other fields.
See package-json.md
for more on package configs.
current lifecycle event
Lastly, the npm_lifecycle_event
environment variable is set to whichever stage of the cycle is being executed. So, you could have a single script used for different parts of the process which switches based on what's currently happening.
Objects are flattened following this format, so if you had {"scripts":{"install":"foo.js"}}
in your package.json, then you'd see this in the script:
process.env.npm_package_scripts_install === "foo.js"
Examples
For example, if your package.json contains this:
{"scripts": {"install": "scripts/install.js","postinstall": "scripts/install.js","uninstall": "scripts/uninstall.js"}}
then scripts/install.js
will be called for the install and post-install stages of the lifecycle, and scripts/uninstall.js
will be called when the package is uninstalled. Since scripts/install.js
is running for two different phases, it would be wise in this case to look at the npm_lifecycle_event
environment variable.
If you want to run a make command, you can do so. This works just fine:
{"scripts": {"preinstall": "./configure","install": "make && make install","test": "make test"}}
Exiting
Scripts are run by passing the line as a script argument to sh
.
If the script exits with a code other than 0, then this will abort the process.
Note that these script files don't have to be Node.js or even JavaScript programs. They just have to be some kind of executable file.
Best Practices
- Don't exit with a non-zero error code unless you really mean it. Except for uninstall scripts, this will cause the npm action to fail, and potentially be rolled back. If the failure is minor or only will prevent some optional features, then it's better to just print a warning and exit successfully.
- Try not to use scripts to do what npm can do for you. Read through
package.json
to see all the things that you can specify and enable by simply describing your package appropriately. In general, this will lead to a more robust and consistent state. - Inspect the env to determine where to put things. For instance, if the
npm_config_binroot
environment variable is set to/home/user/bin
, then don't try to install executables into/usr/local/bin
. The user probably set it up that way for a reason. - Don't prefix your script commands with "sudo". If root permissions are required for some reason, then it'll fail with that error, and the user will sudo the npm command in question.
- Don't use
install
. Use a.gyp
file for compilation, andprepublish
for anything else. You should almost never have to explicitly set a preinstall or install script. If you are doing this, please consider if there is another option. The only valid use ofinstall
orpreinstall
scripts is for compilation which must be done on the target architecture.
See Also
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