Dealing with float precision in Javascript [duplicate]

Question

I have a large amount of numeric values y in javascript. I want to group them by rounding them down to the nearest multiple of x and convert the result to a string.

How do I get around the annoying floating point precision?

For example:

0.2 + 0.4 = 0.6000000000000001 

Two things I have tried:

>>> y = 1.23456789  >>> x = 0.2  >>> parseInt(Math.round(Math.floor(y/x))) * x;  1.2000000000000002 

and:

>>> y = 1.23456789  >>> x = 0.2  >>> y - (y % x) 1.2000000000000002 

Answer 1

From this post: How to deal with floating point number precision in JavaScript?

You have a few options:

• Use a special datatype for decimals, like decimal.js
• Format your result to some fixed number of significant digits, like this: (Math.floor(y/x) * x).toFixed(2)
• Convert all your numbers to integers

Answer 2

You could do something like this:

> +(Math.floor(y/x)*x).toFixed(15); 1.2 

Edit: It would be better to use big.js.

big.js

A small, fast, easy-to-use library for arbitrary-precision decimal arithmetic.

>> bigX = new Big(x) >> bigY = new Big(y) >> bigY.div(bigX).round().times(bigX).toNumber() // => 1.2