for vs forEach

JavaScript performance comparison

Revision 160 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>
  Benchmark.prototype.setup = function() {
    var array = [];
   
    for( var i = 0; i < 1000; i++) {
        array.push(i);
    }
   
    function logIt(val){
        console.log(val);
    }
  };


Array.prototype.forEach2 = function (a, scope) {
            var l = this.length, i = 0;
            if(scope){
                for (; i < l; i++) {
                    a.call(scope, this[i], i);
                }
            }else{
                for (; i < l; i++) {
                    a(this[i], i);
                }
            }
        };
Array.prototype.forEach3 = function (a, scope) {
            var l = this.length, i = 0;
for (; i < l; i++) {
                    scope?a.call(scope, this[i], i):a(this[i], i);
                }
           
        };
</script>

Test runner

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Testing in unknown unknown
Test Ops/sec
for loop
for (i = 0, ii = array.length; i < ii; i++) {
  logIt(array[i]);
}
pending…
forEach
array.forEach(logIt);
pending…
for loop, reverse
for (i = array.length - 1; i >= 0; i--) {
  logIt(array[i]);
}
pending…
for key in object
for (key in array) {
  logIt(array[key]);
}
pending…
forEach with anonymous function
array.forEach(function(val) {
  console.log(val)
});
pending…
foreach2
array.forEach2(logIt);
pending…
foreach3
array.forEach3(logIt);
pending…

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