Array preallocation performance

JavaScript performance comparison

Revision 5 of this test case created

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 initialized))
 
var arr = [],
    l = window.growFactor;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (65x)
 
var arr = [],
    l = 65 * window.growFactor;
arr.length = l;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (65x; Not initialized)
 
var arr = [],
    l = 65 * window.growFactor;
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (65x) alt initialized
 
var l = 65 * window.growFactor, arr = new Array(l)    
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (65x) alt not initialized
 
var arr = new Array(),
l = 65 * window.growFactor;
  
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…
for-loop Fill (1x) alt
 
var l = window.growFactor,
arr = new Array(l);
    
for (var i = 0; i < l; ++i) {
  arr[i] = 0;
}
 pending…

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