for vs forEach

JavaScript performance comparison

Revision 46 of this test case created by wicked

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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Java applet disabled.

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
 
length = values.length;
for (i = 0; i < length; i++) {
    sum += values[i];
}
 pending…
for loop, reverse
 
for (i = values.length - 1; i >= 0; i--) {
    sum += values[i];
}
 pending…
for loop, cached length, callback
 
length = values.length;
for (i = 0; i < length; i++) {
    add(values[i], i, values);
}
 pending…
for loop, cached length, callback.call
 
length = values.length;
for (i = 0; i < length; i++) {
    add.call(context, values[i], i, values);
}
 pending…
$.each
 
$.each(values, function(key, value) {
    sum += value;
});
 pending…
for ... in
 
for (i in values) {
    sum += values[i];
}
 pending…
for loop, reverse, decrement condition
 
for (i = values.length; i--;) {
    sum += values[i];
}
 pending…
for loop, reverse, pre-decrement
 
for (i = values.length - 1; i >= 0; --i) {
    sum += values[i];
}
 pending…
for loop, assignment condition
 
for (i = 0; (value = values[i]) !== undefined; i++) {
    sum += value;
}
 pending…
for loop, assignment condition, reversed
 
for (i = values.length - 1; (value = values[i]) !== undefined; i--) {
    sum += value;
}
 pending…
for loop, assignment condition, callback
 
for (i = 0; (value = values[i]) !== undefined; i++) {
    add(value, i, values);
}
 pending…
for loop, assignment condition, callback.call
 
for (i = 0; (value = values[i]) !== undefined; i++) {
    add.call(context, value, i, values);
}
 pending…
native map function
 
values.map(add);
 pending…
for loop 2
 
for (i = values.length - 1; i--;) {
    sum += values[i];
}
 pending…

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