Is it worth caching the length of an array in a Javascript loop?

JavaScript performance comparison

Revision 148 of this test case created

Info

http://stackoverflow.com/questions/5349425/whats-the-best-to-loop-an-array-in-javascript

Preparation code

<script>
  var myArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35];
  var res = 0;
</script>

Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

Testing in unknown unknown
Test Ops/sec
for i = 0; i < len; i++
 
for (var i = 0; i < myArray.length; i++) {
  res += myArray[i];
}
window.res = res;
 pending…
for i = 0; i < len (cached); i++
 
for (var i = 0, len = myArray.length; i < len; i++) {
  res += myArray[i];
}
window.res = res;
 pending…
for i = 0; i < len (cached outside); i++
 
var len = myArray.length;
for (var i = 0; i < len; i++) {
  res += myArray[i];
}
window.res = res;
 pending…
for i = 0; i !== len (cached); i++
 
for (var i = 0, len = myArray.length; i !== len; i++) {
  res += myArray[i];
}
window.res = res;
 pending…
for i = 0; i !== len; i++
 
for (var i = 0; i !== myArray.length; i++) {
  res += myArray[i];
}
window.res = res;
 pending…

Compare results of other browsers

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:

0 comments

Add a comment