JavaScript Closure Performance Test

Closure is an important concept of language JavaScript. Using closure will give you freedom of writing JavaScript codes efficiently. But what about the extreme performance of JavaScript closure?

For example:

var count = 1000000;
var num = 0;
function withClosure () {
var i = 0;
while (i++ < count) num++;
}

function withoutClosure () {
var count = 1000000;
var i = 0;
var num = 0;
while (i++ < count) num++;
}

Which method will run much faster?

Here is the sample test result of my computer:

Firefox
=======
with closure : 1141
without closure : 375

Internet Explorer
=============
with closure : 969
without closure : 485

It seems that under extreme condition, accessing variable from different closure will have poor performance. So it’s recommended that never access variable from different closure in those frequently-used or time-consuming functions.

Appendix:

window.alert = function (s) {
document.body.appendChild (document.createTextNode (s));
document.body.appendChild (document.createElement (“BR”));
};

function timing (label, action) {
var d = new Date ();
action ();
alert (label + ” : ” + (new Date ().getTime () – d.getTime ()));
}

var count = 1000000;
var num = 0;
function withClosure () {
var i = 0;
while (i++ < count) num++;
}

function withoutClosure () {
var count = 1000000;
var i = 0;
var num = 0;
while (i++ < count) num++;
}
timing (“with closure”, withClosure);
timing (“without closure”, withoutClosure);