Is it worth caching the length of an array in a Javascript loop? (v132)

Revision 132 of this benchmark created by Mayank Singhal on

Description

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

Preparation HTML

<script>
  var myArray = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20];
  var res = 0;
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
With caching
for (var i = 0, len = myArray.length; i < len; i++) {
  res += myArray[i];
}
window.res = res;
ready
Without caching
for (var i = 0; i < myArray.length; i++) {
  res += myArray[i];
}
window.res = res;
ready
Counting down
for (var i = myArray.length; i--;) {
  res += myArray[i];
}
window.res = res;
ready
caching length outside for loop
var len = myArray.length;

for (var i = 0; i < len; i++) {
  res += myArray[i];
}
window.res = res;
ready
while loop
var len = myArray.length;
while (len--) {
  res += myArray[len];
}
window.res = res;
ready
for check index
for (var i = 0; myArray[i++];) {
  res += myArray[i];
}
window.res = res;
ready
upcount while
var len = myArray.length;
var ilen = len;
while (len--) {
  res += myArray[ilen - len];
}
window.res = res;
ready
sublime 2 improved native
for (var i = myArray.length - 1; i >= 0; i--) {
    res += myArray[i];
};
window.res = res;
ready
Cached item value breaks loop
var item;
for (var i = 0; item = myArray[i]; i++) {
  res += item;
}
window.res = res;
ready

Revisions

You can edit these tests or add more tests to this page by appending /edit to the URL.