for vs forEach

JavaScript performance comparison

Revision 135 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
forEach
values.forEach(add);
pending…
for loop, simple
for (i = 0; i < values.length; i++) {
  sum += values[i];
}
pending…
for loop, cached length
for (i = 0; i < values.length; i += 1) {
  sum += values[i];
}
pending…
for loop, reverse
 
pending…
for loop, cached length, callback
 
pending…
for loop, cached length, callback.call
 
pending…
$.each
$.each(values, function(index, value) {
  sum += value;
});
pending…
for ... in
for (key in values) {
  sum += values[key];
}
pending…
for loop, reverse, decrement condition
 
pending…
for loop, reverse, pre-decrement
 
pending…
for loop, assignment condition
 
pending…
for loop, assignment condition, reversed
 
pending…
for loop, assignment condition, callback
 
pending…
for loop, assignment condition, callback.call
 
pending…

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