for vs for..in vs forEach

JavaScript performance comparison

Revision 268 of this test case created by Sam

Preparation code

<script>
  var i, values = [],
      sum = 0;
  for (i = 0; i < 10000; i++) {
   values[i] = i;
  }
  
  function add(val) {
   sum += val;
  }

  function forEachFN(array,fn){
    var l = array.length;
    while(l--){fn(array[l])}
  }
  
  var values2 = JSON.parse(JSON.stringify(values));
  values2.forEach = function(fn){
    var l = this.length;
    while(l--){fn(this[l]);}
  }

</script>
    

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Testing in CCBot 2.0.0 / Other 0.0.0
Test Ops/sec
forEach
values.forEach(add);
pending…
for loop, simple
for (i = 0; i < values.length; i++) {
 add(values[i]);
}
pending…
for loop, cached length
var len = values.length;
for (i = 0; i < len; i++) {
 add(values[i]);
}
pending…
for..in loop
for (i in values) {
 add(values[i]);
}
pending…
forEach more local
(function() {
 var sum = 0;
 values.forEach(function(val) {
  sum += val;
 });
})();
pending…
while --
var l = values.length;
while(l--){ add(values[l]); }
pending…
forEach as function
forEachFN(values, add);
pending…
forEach as prototype
values2.forEach(add)
pending…

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Revisions

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