Bug: decimals are not calculated properly.

[Flimm]

It looks like Heynote uses floating-point arithmetic to calculate equations with decimal numbers. Instead, it should probably use a library like decimal.js in order to make calculations with decimal numbers precisely.

To Reproduce
Steps to reproduce the behavior:

1. Open a maths block in Heynote
2. Type 0.1 + 0.2, and you will see 0.3 displayed. So far so good.
3. Click on the result 0.3 to copy it, and then paste it into a text editor. You will see 0.30000000000000004. This result is incorrect.

Expected behavior
I expect decimal numbers to be calculated properly, without floating-point errors. (I don't want the result to be merely rounded up or down, I want true decimal mathematics using something like decimal.js).

Version: 1.8.0

[NoahAndrews]

Math.js is built on top of decimal.js

[heyman]

It's Math.js that is powering the Math blocks, and they write about round-off errors here:
https://mathjs.org/docs/datatypes/numbers.html#roundoff-errors

A solution is to limit the precision just below the actual precision of 16 digits in the displayed output

Heynote uses a lower precision for the displayed values in order to look nicer, while the copied result uses the full precision. However, maybe the problem would be mitigated by using a slightly lower precision for the copied result as well?

[Flimm]

Math.js uses floating-point arithmetic by default, which is what is causing these imprecise/incorrect results. To get precise and correct results with Math.js, the documentation recommends using Fractions:

Alternatives are to use Fractions which store a number as a numerator and denominator

// Configure the default type of number: 'number' (default), 'BigNumber', or 'Fraction'
math.config({
  number: 'Fraction'
})

// use the expression parser
math.evaluate('0.32 + 0.08') // Fraction, 2/5

I presume that you can use the format method to convert the Fraction number to string in decimal format, like "0.3".