Array preallocation performance

JavaScript performance comparison

Revision 2 of this test case created by Valerio

Preparation code

 
<script>
  Benchmark.prototype.setup = function() {
    window.growFactor = 1000;
  };
</script>

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Testing in unknown unknown
Test Ops/sec
for-loop Fill (1x)
 
var arr = [],
    l = window.growFactor;
arr.length = l;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (1x; Not initialised))
 
var arr = [],
    l = window.growFactor;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (10x)
 
var arr = [],
    l = 10 * window.growFactor;
arr.length = l;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (10x; Not initialised)
 
var arr = [],
    l = 10 * window.growFactor;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (10x) alt initialised
 
var arr = new Array(10 * window.growFactor)    
for (var i = 0; i < arr.length; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (10x) alt not initialised
 
var arr = new Array(),
l = 10 * window.growFactor;
  
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (1x) alt
 
l = window.growFactor;
var arr =  new Uint32Array(l);
    
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…

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