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

JavaScript performance comparison

Revision 82 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];
</script>

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 - 1; i >= 0; i--) {

}
 pending…
caching length outside for loop
 
var len = myArray.length;

for (var i = 0; i < len; i++) {

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

}
 pending…
Counting Down (variable declared outside for)
 
var i; //Same scope
for (i = myArray.length - 1; i >= 0; i--) {

}
 pending…
Counting Down (postfix)
 
for (var i = myArray.length - 1; i >= 0; --i) {

}
 pending…

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