Optimizing Iterating through an Array

25th September 2005 | 2 Comments

I love using arrays, they're just so handy. I recently ran into the problem of finding out if a value already existed in an array. I thought this would be a great time to compare the speed of different loops. I decided to test a For Loop, a While Loop and a different than usual While Loop, where I increment the array’s position in the loop’s condition statement.

I tested these loops on Firefox 1.0.6, Internet Explorer 6, Flash Player 7 and Flash Player 8. Each method was tested three times on a 250,000 item array and I averaged the results. Note: These results are tied directly to the speed of your computer, so speeds may vary.

I was thoroughly impressed by Firefox, even in its non optimized state, nothing could touch it. The same can’t be said about Flash. I believe flash’s slowness stems from the fact that the array is being executed on a virtual machine instead of native code. But I’m glad to see the Flash 8 Player got some needed speed boosts in its lastest update.

Here my super optimized method (While Loop #2):

Array.prototype.find = function(x) {
	var length = this.length;
	var i = -1;

	while(++i < length) {
		if (this[ i ] == x) {
			return true;
		}
	}
	return false;
}

Here is While Loop #1:

Array.prototype.find = function(x) {
	var i = 0;
	var j = this.length;

	while(i < j) {
		if (this[ i ] == x) {
			return true;
		}
		i++;
	}
	return false;
}

And here is the For Loop:

Array.prototype.find = function(x) {
	for(var i = 0; i < this.length; i++) {
		if (this[ i ] == x) {
			return true;
		}
	}
	return false;
}

Update: I ran the test again, but this time iterating backwards. All of the For Loops showed minor improvements (20ms - 30ms faster) except for Flash 7 Standalone player, it jumped from 391ms down to 303ms. While Loops weren’t so fortunate. They all hovered around the same speed as the backwards For Loop.