javascript - Floating-point error mess

Question

I have been trying to figure this floating-point problem out in javascript. This is an example of what I want to do:

var x1 = 0
for(i=0; i<10; i++)
{
    x1+= 0.2    
}

However in this form I will get a rounding error, 0.2 -> 0.4 -> 0.600...001 doing that.

I have tried parseFloat, toFixed and Math.round suggested in other threads but none of it have worked for me. So are there anyone who could make this work, because I feel that I have run out of options.

Answer 1

You can almost always ignore the floating point "errors" while you're performing calculations - they won't make any difference to the end result unless you really care about the 17th significant digit or so.

You normally only need to worry about rounding when you display those values, for which .toFixed(1) would do perfectly well.

Whatever happens you simply cannot coerce the number 0.6 into exactly that value. The closest IEEE 754 double precision is exactly 0.59999999999999997779553950749686919152736663818359375, which when displayed within typical precision limits in JS is displayed as 0.5999999999999999778

Indeed JS can't even tell that 0.5999999999999999778 !== (e.g) 0.5999999999999999300 since their binary representation is the same.