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

JavaScript performance comparison

Revision 95 of this test case created

Info

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

Preparation code

<script>
  var a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
  a = a.concat(a, a, a, a, a, a, a, a);
  var myArray = a;
</script>

Test runner

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Testing in unknown unknown
Test Ops/sec
With caching
 
var total = 0;
for (var i = 0, len = myArray.length; i < len;) {
  total += myArray[i++];
}
 pending…
Without caching
 
var total = 0;
for (var i = 0; i < myArray.length;) {
  total += myArray[i++];
}
 pending…
Counting down
 
var total = 0;
for (var i = myArray.length, a; a = myArray[--i];) {
  total += a;
}
 pending…
caching length outside for loop
 
var total = 0,
    len = myArray.length;
for (var i = 0; i < len;) {
  total += myArray[i++];
}
 pending…
while loop
 
var total = 0,
    len = myArray.length;
while (len--) {
  total += myArray[len];
}
 pending…
for check index
 
var total = 0;
for (var i = 0, a; a = myArray[i++];) {
  total += a;
}
 pending…

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