For minification, as someone else said. I originally wrote this for a JS1K competition some years ago, so it's not geared towards readability, but towards small code size.

I had a really, really ugly trick that saved me a couple of bytes which I removed before posting to HN. I figured out I was using canvas.getImageData() and canvas.putImageData(). So I did this: var tID = "tImageDatA"; canvas["ge"+tID](); canvas["pu"+tID"](); You can see that in the original source: http://gabrielgambetta.com/tiny_raytracer_full.js

Not my proudest hack :D