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

JavaScript performance comparison

Revision 7 of this test case created

Info

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

Preparation code

<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script><script src="//ajax.googleapis.com/ajax/libs/prototype/1.6.1.0/prototype.js"></script><script src="//ajax.googleapis.com/ajax/libs/mootools/1.3.1/mootools-yui-compressed.js"></script><script src="//ajax.googleapis.com/ajax/libs/yui/2.8.1/build/yuiloader/yuiloader-min.js"></script><script src="//ajax.googleapis.com/ajax/libs/dojo/1.6/dojo/dojo.xd.js"></script><script src="//ajax.googleapis.com/ajax/libs/ext-core/3.1.0/ext-core.js"></script>
<script>
  var myArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];
</script>

Preparation code output

Test runner

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

}
 pending…
Prefix incr
 
for (var i = 0, len = myArray.length; i < len; ++i) {

}
 pending…

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