Hello guys,
I've just stumbled upon an unbelievable JavaScript performance bug (or
feature, I can't decide).
I was trying to improve the performance of a Class constructor like this one:
---
CreateClass = function(parentClass, config) {
//Code here to clean and validate arguments
//Uncomment this to be 10x faster
//var totallyInventedName = function() {
//
//}
var classConstructor = function() {
//A lot of stuff to copy 'config' to my prototype
}
//A lot of tweaks with classConstructor.prototype
return classConstructor;
}
var Class = CreateClass(null, { /*methods here*/});
var instance = new Class();
---
Creating 100 instances takes about 300ms (FF 3.6, measured with
FireBug and internal timers using Date()). The weird thing is that if
I add a function definition before defining classConstructor
(commented in the example), the code only takes 30ms to run, and no
code is calling this new function (100% sure about this point). It
makes no sense, the new code should be slower because it's creating
100 new functions.
I've checked everything several times, restarted Firefox, started with
a new Firefox profile, even reinstalled Firefox, and the results are
consistent: 300ms without the function, 30ms whit it.
It makes completely no sense to me. Can someone please shed some light
into this?
--
S.Cinos
JavaScript Developer at Tuenti.com
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