Array direct assignment vs push

JavaScript performance comparison

Revision 6 of this test case created by Jesse Dailey

Preparation code

 
<script>
Benchmark.prototype.setup = function() {
    var array = [];
    var other_array = 0;
    var count = 100;
};
</script>

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Testing in unknown unknown
Test Ops/sec
Direct assignment
for(var i = 0; i < count; i++)
{
  array[i] = Math.random();
}
pending…
Push
for(var i = 0; i < count; i++)
{
  array.push(Math.random());
}
pending…
Direct assignment (calculated)
for(var i = 0; i < count; i++)
{
  array[array.length] = Math.random();
}
pending…
other
// It makes no sense for this to be 20x slower,
// since the the only difference is one extra increment.
// Something is wrong with this benchmark.
for(var i = 0; i < count; i++) {
  array[other_array++] = Math.random();
}
// This is some inefficiency in jsperf (a hidden closure?)
// not the test code.
 
pending…
other2
// This is what the 'other' test _meant_ to measure.
var j = 0;
for( var i = 0; i < count; i++) {
  array[j++] = Math.random();
}
pending…

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