WTFJS

2011-08-28 12:52

Inspired by this site, I've decided to share my own "WTF, JS!" moment.

My example involves unexpected behaviour in console.log. Consider the following snippet.

	a = [];
	for(i = 0; i < 5; i++){
		a.push(i);
		console.log(a);
	}

Pretty straightforward, right? Think about what output you would expect when running that code. Maybe it would look a little like this?

	[0]
	[0, 1]
	[0, 1, 2]
	[0, 1, 2, 3]
	[0, 1, 2, 3, 4]

Seems reasonable. But console.log, it would seem, prints asynchronously. So your actual output will look like this.

	[0, 1, 2, 3, 4]
	[0, 1, 2, 3, 4]
	[0, 1, 2, 3, 4]
	[0, 1, 2, 3, 4]
	[0, 1, 2, 3, 4]

I should, apparently, stop using this for debugging. What the fuck.

Edit: It's been brought to my attention that this produces the output you would expect in Firebug so this is more of a "WTF, Chrome!" moment.