http://axod.net/arraytest.html http://axod.net/arraytest.html After 20 iterations: Browser Pre-alloc No pre-alloc Firefox 3.6.13 OSX

http://axod.net/arraytest.html http://axod.net/arraytest.html After 20 iterations: Browser Pre-alloc No pre-alloc Firefox 3.6.13 OSX 824ms 829ms Safari 5.0.3 OSX 812ms 948ms Chrome 9.0.597.16 OSX 1317ms 992ms I'm pretty sure that in modern browsers new Array(length) doesn't allocate anything, it just sets the length property. The results I'm seeing would agree with Google really. Perhaps you were seeing GC events slowing down the test? The other thing about for(var i=0;i<arr.length;i++) is it can end up as an infinite loop if you're modifying the length inside the for loop: for (var i=0;i<arr.length;i++) { arr[10 + i*2] = "foo"; } // Infinite loop.