for loop research

JavaScript performance comparison

Test case created

Info

Varius for-loop variants: * with length caching * with various counter increment (++i, i++) * while alternative

Preparation code

 
<script>
  Benchmark.prototype.setup = function() {
    var arr = [];
    
    for (var i=0; i<1000; i++) {
      arr.push('arr-value-' + i);
    }
    
    function worker() {
      return(1+1);
    }
  };
</script>

Test runner

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Testing in unknown unknown
Test Ops/sec
classic for-loop
 
for (var i=0; i < arr.length; i++) {
  worker();
}
 pending…
++i
 
for (var i=0; i < arr.length; ++i) {
  worker();
}
 pending…
caching length in loop
 
for (var i=0, len=arr.length; i<len; i++) {
  worker();
}
 pending…
caching length outside loop
 
var len=arr.length;

for (var i=0; i<len; i++) {
  worker();
}
 pending…
double caching length
 
var len=arr.length;

for (var i=0, ilen=len; i<ilen; i++) {
  worker();
}
 pending…
while alternative i--
 
var i = arr.length;
while (i--) {
  worker();
};
 pending…
while alternative --i
 
var i = arr.length;
while (--i) {
  worker();
};
 pending…

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Revisions

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