Number precision in JavaScript

Question

Why 100 == 99.999 is true, however 100 == 99.99 is false in Javascript?

Answer 1

What Every Computer Scientist Should Know About Floating Point Arithmetic

and the shorter, more to the point:

http://floating-point-gui.de/

Answer 2

Where are you getting that result?

From Firebug console in Firefox 3.6.3

>>> 100==99.99
false
>>> 100==99.999
false
>>> 100==99.9999
false
>>> 100==99.99999
false
>>> 100==99.999999
false
>>> 100==99.9999999
false
>>> 100==99.99999999
false
>>> 100==99.999999999
false
>>> 100==99.9999999999
false
>>> 100==99.99999999999
false
>>> 100==99.999999999999
false
>>> 100==99.9999999999999
false
>>> 100==99.99999999999999
false
>>> 100==99.999999999999999
true

Answer 3

Why is 100 == 99.999 true in Javascript?

It's not; whatever Javascript implementation you are using is buggy.

however 100 == 99.99 is false in Javascript?

Because they're not equal.