The Problem
If we are dealing with the module operator we could have this case:alert(
8.25 % .05
);
// 0.049999999999999545
We expected 0 but we have a floating point inconsistency instead. This is a well known problem, and not only with JavaScript, truly annoying when we have to show run-time computed money/trends operations.
The Solution
This comes from my reply in a JS forum, knowing that the module will be a simply floating point, let's say .1 to .001, if we remove floating point from the right side of the operation everything works just fine:
function mod(num, mod){
// Another WebReflection silly idea
var pow = Math.pow(10, (("" + mod).split(".")[1] || "").length);
return ((num * pow) % (mod * pow)) / pow;
};
alert(
mod(8.25, .05)
); // 0
alert(
mod(8.25, .1)
); // 0.5
That's it, have a nice Sunday
6 comments:
I think it would be better to just work in cents all the time instead of working in Euros/Dollars. That way all your operations are protected from floating point inaccuracy instead of just the % operator.
this is a quick and dirty fix, not a best practice suggestion or a universal solution ... if people had this problem, they can fix it, that's the purpose of a Q&D code :)
thank you for the q&d, there's a typo in the code comments. // 0.5 should be // 0.05 :)
I appreciate the Q&D suggestion, but Erik is right. Use cents, not whole currency.
Also, a spelling nit-pick :) The operator is called modulo.
guys, this is a solution for a forum question, that's it
Please keep posting the Q&D's. Those of use who don't work in JS every day forget the little tricks like ("" + castMeToString)
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