Another reason to loop backwards is when you DO need to change the array within the loop. For example, say you needed to remove all elements of an array whose value was “killme”. You’d need to loop through the array, but you’d also need to change the array. When you remove items from the array, your indexing gets messed up if you are moving forwards. but backwards is like:

for(var i:Number = items.length-1; i >= 0; i–)
{
if(items[i] == “killme”) items.splice(i, 1);
}

If I wrote that correctly (i’m rushing…) it should remove the elements correctly, and not mess up the indexing in the process.

Lately, I’ve been trying to remember to grab the array length before looping. I don’t know if it helps much, but for some reason I feel better doing it.

I would also like to add a thank you to Keith for his example. That’s a great trick, and I’ll do my best to remember to use it in the future. Thanks, man!

Good example.

You know, you and I are the kind of guys who would sit around a camp fire and talk about “when it’s a good idea to loop backwards through an array.” :-)

My wife is rolling here eyes as she reads this.

Of all the code-optimization tips, storing an array’s length in a variable is the biggest performance boost. You can apply the rule of threes here: if you expect to access a calculated value (like a clip’s _x or an array’s length) 3 or more times, store it in an array. Perhaps the inverse is easier to understand: if you only plan to access a variable’s value 1 or 2 times, no sense storing it in a variable in the first place.

Great tip. This is especially effective when checking the length of long strings.

You can see some other performance tips with times on this great site:

http://www.oddhammer.com/actionscriptperformance/set3/

Cheers,

Dustin Senos

Phillip, “rule of three” sounds like something for Lord of the Rings but I like it. :-)

I think that in many instances it can also aid in code readability to create local variables.

Dustin, thanks for the link. Good stuff.