Adding 0.1 incrementally with setState gives out approximate numbers about react

[sophiebits]

This is standard behavior for JavaScript (unrelated to React), and is expected.

Floating-point numbers such as 0.1 and 0.2 can't be represented exactly in binary, so an approximation is used. It's as if you (in base 10) added 0.333 + 0.333 + 0.333 and got 0.999 instead of 1 -- just an artifact of the rounding that happens. Here's a Stack Overflow question explaining this phenomenon: http://stackoverflow.com/q/588004/49485

[zpao]

@ldhieu Yea, this is expected behavior with JS. One common solution when working with decimals (eg, currency) is to just use whole numbers, then divide by some number when you need to display the number to a use. $1.01 would be stored as 101 and then when displaying that to the user you would do num / 100.