This example is using box2d for something that can be implemented with very simple code dropping this important dependency IMHO. Box2d is a great fit when real 2D physics simulation is needed, but for apples falling at constant speed and jumps, it's not worth it.
I've been watching for a good Box2d javascript port for the last couple years, and so far there's nothing out there that's anywhere close to useable. It's a shame really, since the Flash version is so good.<p>Every port is either a bunch of Regular expressions run against the ActionScript source, or a wacky hand port of a version several years out of date. In either case, as soon as you plug it into anything more complicated than the Hello World demos it starts demonstrating in myriad wacky ways that nobody must have ever tried using it on a real project.
I keep checking back, doing the rounds of GitHub and the web in general every couple months hoping in vain that somebody will have put something good out, but thus far no luck.<p>And of course, I'm part of the problem, complaining about the situation but not actually downloading the ActionScript source myself and putting together a decent port.