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

From the Floating-Point Guide:

What can I do to avoid this problem?

That depends on what kind of calculations you’re doing.

• If you really need your results to add up exactly, especially when you work with money: use a special decimal datatype.
• If you just don’t want to see all those extra decimal places: simply format your result rounded to a fixed number of decimal places when displaying it.
• If you have no decimal datatype available, an alternative is to work with integers, e.g. do money calculations entirely in cents. But this is more work and has some drawbacks.

Note that the first point only applies if you really need specific precise decimal behaviour. Most people don't need that, they're just irritated that their programs don't work correctly with numbers like 1/10 without realizing that they wouldn't even blink at the same error if it occurred with 1/3.

If the first point really applies to you, use BigDecimal for JavaScript or DecimalJS, which actually solves the problem rather than providing an imperfect workaround.