for vs forEach

JavaScript performance comparison

Revision 156 of this test case created

Info

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

Inspired by Adrian Sutton's tests at: http://www.symphonious.net/2010/10/09/javascript-performance-for-vs-foreach/

This one adds random floating point numbers to see if the loop overhead is significant at all in the face of standard work.

Preparation code

<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script>
Benchmark.prototype.setup = function() {
    var i,
      key,
      random,
      array = [],
      object = {},
      sum = 0;
   
    for (i = 0; i < 10000; i++) {
      random = Math.random();
      array[i] = random;
      object[i] = random;
    }
   
    function add(val) {
      sum += val;
    }
};

Benchmark.prototype.teardown = function() {
    i = 0;
    array = [];
    object = {};
    sum = 0;
};
</script>

Test runner

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Testing in unknown unknown
Test Ops/sec
forEach
array.forEach(add);
pending…
for loop, simple
for (i = 0; i < array.length; i++) {
  add(array[i]);
}
pending…
for loop, reverse
for (i = array.length - 1; i >= 0; i--) {
  add(array[i]);
}
pending…
for key in object
for (key in object) {
  add(object[key]);
}
pending…
forEach with anonymous function
array.forEach(function(val) {
  sum += val;
});
pending…

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