The (New) Standard `for` Loop

for (var i = 0, j = foo.length; i < j; i++) {
  // do stuff
}

for (var i = foo.length; i;) {
  // first usage in loop: blah[--i]
  // do stuff slightly faster in reverse order
}

https://gist.github.com/603041/e355b4478af9290389f695df14a9d7c682975e78

I'm not sure about this. Seems like that second loop is the slowest of all (at least in Chrome).
http://jsperf.com/for-loop-test/2

Fixed your test cases:

http://jsperf.com/for-loop-test/3

Not sure how that fixed it. It still seems like it's the slowest. Also, I'd opt for the cleaner syntax instead of decrementing inside of the loop.

it wasn't slowest for me, it was 1% faster in the chrome6 test i initially ran. it definitely wasn't the 20% slower that your revision had.

also, i didn't claim it was better/cleaner syntactically. it is shorter, and at least as fast if not faster. but any such for-loop optimizations have to be taken with the grain of salt that the code will only be written and maintained by people who understand such syntax.

just updated again to fix minor issues.

http://jsperf.com/for-loop-test/4

Again, the last test is performing almost the same as the others, and sometimes 1% faster. definitely not statistically slower.

That might be the case in the particular version of Chrome 6 you were using to test. In the tests I performed, however, there was a greater than 1% difference.