for vs forEach

JavaScript performance comparison

Revision 10 of this test case created

Info

Is it faster to use the native forEach or just loop with for?

Preparation code

<script>
  var i, values = [],
      sum = 0;
  for (i = 0; i < 10000; i++) {
   values[i] = i;
  }
 
  function add(val) {
   sum += val;
  }
 
  function forEach(array, fct) {
   for (var i = 0; i < array.length; i++) {
    fct(array[i]);
   }
  }
</script>

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Testing in unknown unknown
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 loop, reverse
for (i = values.length - 1; i >= 0; i--) {
 add(values[i]);
}
pending…
forEach more local
(function() {
 var sum = 0;
 values.forEach(function(val) {
  sum += val;
 });
})();
pending…
forEach function
forEach(values, add);
pending…

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Revisions

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1 comment

AlK commented :

Each test case is executed in a closure, and the i variable is declared globally, that's why Array.prototype.forEach method is faster sometimes (it does not have to search for the variable in the global scope).

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