Is it worth caching the length of an array in a Javascript loop? (v185)

Revision 185 of this benchmark created 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, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35];
  var res = 0;
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
for i = 0; i < len; i++
for (var i = 0; i < myArray.length; i++) {
  res += myArray[i];
}
window.res = res;
ready
for i = 0; i < len (cached); i++
for (var i = 0, len = myArray.length; i < len; i++) {
  res += myArray[i];
}
window.res = res;
ready
for i = len; i--
for (var i = myArray.length; i--;) {
  res += myArray[i];
}
window.res = res;
ready
for i = 0; i < len (cached outside); i++
var len = myArray.length;
for (var i = 0; i < len; i++) {
  res += myArray[i];
}
window.res = res;
ready
while len--
var len = myArray.length;
while (len--) {
  res += myArray[len];
}
window.res = res;
ready
for i = 0; array[i++]
for (var i = 0; myArray[i++];) {
  res += myArray[i];
}
window.res = res;
ready
while len--, access array[ilen-len]
var len = myArray.length;
var ilen = len;
while (len--) {
  res += myArray[ilen - len];
}
window.res = res;
ready
while len--, access array[0], array.shift
var len = myArray.length;
while (len--) {
  res += myArray[0];
  myArray.shift();
}
window.res = res;
ready
for i = 0; i !== len (cached); i++
for (var i = 0, len = myArray.length; i !== len; i++) {
  res += myArray[i];
}
window.res = res;
ready
for i = 0; i !== len (cached outside); i++
var i = 0, len = myArray.length;
for ( i; i !== len; i++) {
  res += myArray[i];
}
window.res = res;
ready
for i = 0; i !== len; i++
for (var i = 0; i !== myArray.length; i++) {
  res += myArray[i];
}
window.res = res;
ready
mangled loop
var i = 0, len = myArray.length, _tmp
while(true) {
  _tmp = (i < len)
  if(!_tmp) {
    break
  }
  res += myArray[i]
  ++i
}
window.res = res;
ready

Revisions

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