Performance of Array vs. Object

JavaScript performance comparison

Revision 4 of this test case created by Valeriu Paloş


After seeing, I thought the test could be improved.

I thought it was conspicuous that on Chrome, the Object iteration with known length was faster that a pure array (unlike in FireFox). The problem was the arr.length property was accessed on every iteration (and Firefox was optimizing it).

Preparation code

Benchmark.prototype.setup = function() {
    var arr = [],
        obj = {};
    for(i = 0; i < 10000; i += 1) {
        var o = {payload:i};
        obj[i] = o;

Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

Testing in unknown unknown
Test Ops/sec
Array Performance
var sum = 0;
var length = arr.length;
for (var x=0; x<length; ++x) {
    sum += arr[x].payload
Object Performance
var sum = 0;
for (var x in obj) {
    sum += obj[x].payload;
Object Performance using known length
var sum = 0;
for (var x=0; x<10000; ++x) {
    sum += obj[x].payload
Using Object.keys()
var sum = 0;
var keys = Object.keys(obj);
for (var x=0; x<keys.length; ++x) {
    sum += obj[keys[x]].payload

Compare results of other browsers


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