Array Assignment vs Array Push

JavaScript performance comparison

Revision 4 of this test case created by Timo

Info

You've heard the rumors - now here's the proof.

v3 adds pre-allocation

Preparation code

 
<script>
  Benchmark.prototype.setup = function() {
    var size = 2000;
  };
</script>

Test runner

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

Java applet disabled.

Testing in unknown unknown
Test Ops/sec
arrayA[i] = 'foo';
 
var arrayA = [];
for (var i = 0; i < size; i++) {
  arrayA[i] = 'foo';
}
 pending…
arrayB.push('foo');
 
var arrayB = [];
for (var i = 0; i < size; i++) {
  arrayB.push('foo');
}
 pending…
arrayC[i] = 'foo'; (preallocated)
 
var arrayC = new Array(size);
for (var i = 0; i < size; i++) {
  arrayC[i] = 'foo';
}
 pending…
Inline
 
var arrayD = ["foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","foo","fo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 pending…

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