for vs forEach

JavaScript performance comparison

Revision 189 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,
      value,
      length,
      values = {},
      sum = 0,
      context = values;
   
   
    for (i = 0; i < 10000; i++) {
      values[i] = Math.random();
    }
   
    function add(val) {
      sum += val;
    }
};

Benchmark.prototype.teardown = function() {
    i = 0;
    value = 0;
    length = 0;
    values = {};
    sum = 0;
};
</script>

Test runner

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Testing in unknown unknown
Test Ops/sec
for cached length
for (var i = 0, l = values.length; i < l; ++i) {
  sum += values[i];
}
pending…
for
for (var i = 0; i < values.length; i++) {
  sum += values[i];
}
pending…

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