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

JavaScript performance comparison

Revision 10 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 = [];
  while (myArray.length < 10000)
  myArray[myArray.length] = Math.random();
</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…
Prefix incr
 
for (var i = 0, len = myArray.length; i < len; ++i) {}
 pending…
for in
 
for (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