http://milan.adamovsky.com/2011/12/fastest-loop-in-javascript.html

The loop construct looks like this:

var counter = 10;

redo:
while (counter–)
{
… your code …

continue redo;
}

I haven’t tried all the various loop constructs (e.g. for, do, etc) to see which one is the absolute winner – as the main goal was to prove that the use of a label increases the performance dramatically.

If I need to loop through 1000 item array, 100 times (which is rare if never) I’ll start using reverse whiles. :)

http://www.mdk-photo.com/Vector3_2 (went from 20ball to 50 at the same fps)

http://www.mdk-photo.com/Editor (doing the impossible every day i code on it…)

I’ve read : http://www.devwebpro.com/devwebpro-39-20030514OptimizingJavaScriptforExecutionSpeed.html
and every application since, executes faster now !

Reverse loop is as good as a For(Assignment) imo.

1) The best kind of speed optimization is more efficient algorithm design. Before you go nuts trying to squeeze every last ounce of speed out of every statement, take a serious look at the design of your algorithms first. Why? See next point.
2) Speed optimization is usually the last step and the last resort while programming. Code that has been altered explicitly for speed concerns is almost always difficult to read, maintain and overhaul. If you plan on sharing your code with others, this is something you should think about seriously.
3) For most uses of JavaScript, speed optimization is just not necessary. If you are feeling the urge to speed up your code just for the sake of it, don’t. It’s not worth it. If, however, speed is critical to your project, and you can’t seem to get the necessary speed from your design, then your code is a good candidate for speed optimization.

Now that would be usefull, because applications grow bigger and the memory get more stuffed..

Cheers

Eg something like
while (node.next) {
.. process node.item …
node = node.next
}

Also, you can make sure that you always use the same kind of loop over arrays by providing functional style mapping functions eg:

Arrays = {
// implement array loop using downwards while
loop: function(ary, lambda) {
var l = ary.length;
var i, n;
if (l > 0) {
i = l;
do {
n = l – i;
lambda(ary[n], n);
i -= 1;
} while (i);
}
}
}
eg:
Arrays.loop([1,2,3], function(i) { console.log(i) });

This way you can keep the loop code seperate so it can be improved or modified. You lose the ability to break out of a loop half way through but this can be achieved with return values or exceptions.

http://home.earthlink.net/~kendrasg/info/js_opt/jsOptMain.html

But it’s a total nightmare to implement.

I never really understood why the reverse while didn’t catch on more. It’s easy to use, doesn’t really need any more code and it much faster than a regular for loop.