It is pretty much a direct port of the Processing language (originally written in Java). So you can bring your Processing projects to the browser without the need for an applet.
Oh, I know that - was just wondering why I'd be better off starting a new project in processing.js instead of in plain js/canvas.
It's a lot easier to see the point with java/processing, since java2d is quite a bit harder to work with (or rather, it has many more gotcha's) than js/canvas.
Personally, I use processing.js because I can use all the existing Processing examples as a point of reference. It is easier to get the ball rolling as opposed to starting from scratch.
As a plus, the experience I get with processing.js, I will be able to apply to Processing (as you probably know, Processing is often used to graph output from an Arduino board, something else I have as a hobby).
