The JS test is the same as the AS2 and AS3 tests in that all of them use essentially the same loop code. I like to think of the while (i--) aprpcaoh as more of a feature of backwards looping than a hack. Perhaps I'll do a followup to this article to dig into the bytecode generated by each of these loops. It's quite likely that you're right about them: the backwards loop is probably doing less work.