Fastest array loops in JS really using array

JavaScript performance comparison

Revision 90 of this test case created by fredoche

Info

Testing the best overall performers (across both desktop and mobile) from these jsperf tests:

Caching array length

Different kinds of loop

Interestingly, it would seem that current 2012 browsers have all optimized their Javascript engines for basic for and while loop syntax. This means we can probably abandon all the 'trick' loops (that used to run faster) and just go with whatever loop syntax we find the most readable.

Preparation code

<script>
  // Populate the base array
  var arr = [];
  for( var i = 0; i < 1000; i++ ) {
    arr[i] = 'value' + i;
  }

  function someFn (ix) {
      return ix * 5 + 1 / 3 * 8;
  }
</script>

Test runner

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Java applet disabled.

Testing in unknown unknown
Test Ops/sec
For loop, basic
for (var i = 0; i < arr.length; i++) {
  var temp = arr[i]+someFn(i);
}
pending…
While loop, basic
var i = 0;
while (i < arr.length) {
  var temp = arr[i]+someFn(i);
  i++;
}
pending…
For loop, cached
for (var i = 0, len = arr.length; i < len; i++) {
  var temp = arr[i]+someFn(i);
}
pending…
For loop, i--
for (var i = arr.length - 1; i >= 0; i--) {
  var temp = arr[i]+someFn(i);
}
pending…
Do-while loop, i--
var i = arr.length - 1;
do {
  var temp = arr[i]+someFn(i);
}
while (i--);
pending…
Do-while loop, --i
var i = arr.length;
if (i > 0) {
  do {
    var temp = arr[i]+someFn(i);
  }
  while (--i);
}
pending…
Magic For Loop
for (var i = arr.length; i--;) {
  var temp = arr[i]+someFn(i);
}
pending…
recursive loop
function browse_array (array_length, index){
    var temp = arr[index]+someFn(index);
    if (index<array_length){
        browse_array(array_length,++index);
    }
    return false;
 };
browse_array (arr.length,0);
pending…

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Revisions

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