Info

Was trying to come up with some sort of syntactic sugar that comes closer to the prettiness of Array.forEach(fn) syntax but with the performance closer to native for-loop.

Clearly "forEach2" is not it, yet. It's currently terribly worse than either a for-loop or even forEach. :)

It's mainly because for-in-loop performance is terrible compared to for-loop: http://jsperf.com/for-loop-vs-for-in-loop

Preparation code

<script>
  Array.prototype.forEach2 = function(fn, thisObj) {
   var k = {};
   for (var i = 0, len = this.length; i < len; i++) this.hasOwnProperty(i) && (k[i] = 0);
   fn.call(thisObj, void 0, 0, this, k);
   return this;
  };
  
  var arr = ['1', true, false, "", void 0, null, 2, 18.5936];
  
  delete(arr[3]);
  
  var arr2 = arr.slice();
  
  for (var j = 0; j < 500; j++) {
   arr2.push(Math.round(Math.random()));
  }
  
  var arr3 = arr2.slice();
  
  for (var m = 0; m < 5000; m++) {
   arr3.push(Math.round(Math.random()));
  }
</script>

Test runner

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arr.forEach(function(v, i, a) {
 v;
});

arr2.forEach(function(v, i, a) {
 v;
});

arr3.forEach(function(v, i, a) {
 v;
});

for (var i = 0, len = arr.length, v; i < len; i++) {
 v = arr[i];
}

for (var i = 0, len = arr2.length, v; i < len; i++) {
 v = arr2[i];
}

for (var i = 0, len = arr3.length, v; i < len; i++) {
 v = arr3[i];
}

arr.forEach2(function(v, i, a, k) {
 for (i in k) {
  v = a[i];
 }
});

arr2.forEach2(function(v, i, a, k) {
 for (i in k) {
  v = a[i];
 }
});

arr3.forEach2(function(v, i, a, k) {
 for (i in k) {
  v = a[i];
 }
});

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Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

• Revision 1: published by Kyle Simpson on 7th August 2010
• Revision 3: published on 14th October 2011
• Revision 4: published on 23rd February 2012

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