Fastest array loops in Javascript

JavaScript performance comparison

Revision 120 of this test case created by Andrew Grothe

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++) {
  someFn(i);
}
pending…
While loop, basic
var i = 0;
while (i < arr.length) {
  someFn(i);
  i++;
}
pending…
For loop, cached
for (var i = 0, len = arr.length; i < len; i++) {
  someFn(i);
}
pending…
For loop, i--
for (var i = arr.length; i > 0; i--) {
  someFn(i);
}
pending…
Do-while loop, i--
var i = arr.length - 1;
do {
  someFn(i);
}
while (i--);
pending…
Do-while loop, --i
var i = arr.length;
if (i > 0) {
  do {
    someFn(i);
  }
  while (--i);
}
pending…
For..in loop
for (var i in arr) {
  someFn(i);
}
pending…
while loop i--
var i = arr.length;
while (i--) {
  someFn(i);
}
pending…
For loop, i -= 1
for (var i = arr.length; i > 0; i -= 1) {
  someFn(i);
}
pending…
For loop, i -= 1 II
var i;
for (i = arr.length; i > 0; i -= 1) {
  someFn(i);
}
pending…
For loop, i -= 1 III
var i;
var len = arr.length;
for (i = len; i > 0; i--) {
  someFn(i);
}
pending…

Compare results of other browsers

Revisions

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