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

JavaScript performance comparison

Revision 25 of this test case created by oliver_h

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];
</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
With caching
 
for (var i = 0, len = myArray.length; i < len; i++) {

}
 pending…
Without caching
 
for (var i = 0; i < myArray.length; i++) {

}
 pending…
Counting down
 
for (var i = myArray.length; i--;) {

}
 pending…
caching length outside for loop
 
len = myArray.length;
for (var i = 0; i < len; i++) {

}
 pending…
while loop
 
len = myArray.length;
while (len--) {

}
 pending…
for check index
 
for (var i = 0; myArray[i++];) {

}
 pending…
Counting Up without Caching
 
for (var i=-1; myArray.length - ++i;) {

}
 pending…
Counting Up with Caching
 
var l = myArray.length;
for (var i=-1; l - ++i;) {

}
 pending…
without length at all
 
for (var i in myArray) {

}
 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