Array direct assignment vs push

JavaScript performance comparison

Revision 29 of this test case created by kybernetikos

Preparation code

 
<script>
Benchmark.prototype.setup = function() {
    var array = new Array(100);
    var array2 = [];
    array2.len = 0;
    var other_array = 0;
};
</script>

Test runner

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Testing in unknown unknown
Test Ops/sec
Direct assignment
for(var i = 0; i < 100; i++)
{
  array[i] = "test";
}
pending…
Push
for(var i = 0; i < 100; i++)
{
  array.push("test");
}
pending…
Direct assignment (calculated)
for(var i = 0; i < 100; i++)
{
  array[array.length] = "test";
}
pending…
other
for(var i = 0; i < 100; i++)
{
  array[other_array++] = "test";
}
pending…
array2.len
for(var i = 0; i < 100; i++)
{
  array2[array2.len++] = "test";
}
pending…
array2.push
for(var i = 0; i < 100; i++)
{
  array2.push("test");
}
pending…
Reverse
for(var i = 99; i >= 0; --i)
{
  array[i] = "test";
}

// as is common, working in reverse is often faster.  This seems to be particularly the case in ff.
pending…
Assignment to previously stored.
var x = "test";
for(var i = 0; i < 100; i++)
{
  array[i] = x;
}
pending…

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1 comment

kybernetikos (revision owner) commented :

'Reverse' and 'Assignment to previously stored' run particularly quickly on my FF 24.

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