Welcome to JavaScript where
Number.isInteger(0.9999999999999999) is false and
Number.isInteger(0.99999999999999999) is true

The problem it's not javascript itself, but it's the limitation of floating point variable with representation error in decimal base.

So 0.99999999999999999 is rounded to 1

As far as I know that is a problem with Math itself: http://relativelyinteresting.com/do...

Literally "close enough"? ;)

var a = 1;
a=a/3; //a: 0.3333333...
a=a*3; //a: 0.9999999...
Now tell me, is "a" an integer or a decimal?

Wat

Math tells us that 0.(9) = 1, check on your calculator.

Do you know why?
1/9 = 0.(1)
2/9 = 0.(2)
3/9 = 0.(3)
...
9/9 = 1 = 0.(9)

Isn't that interesting?

Math is broken.

@adampisula The real proof is

x = 0.(9)
10x = 9.(9)
10x - x = 9x = 9.(9) - 0.(9) = 9
x = 1

Holy shit my mind has been blown by all these proofs 😱

@BingBangTheory Actually it's the same, but you're right!

I think it has something to do with our base10 decimal system vs calculator/machine base2 (binary) repesentation of base10 number. So "close enough" is as acurate as is possible. But javascript does have some odd quirks lol.