setAnimation; a sensible requestAnimation polyfill

setAnimation.js

// rAF polyfill based on https://gist.github.com/1579671

(function(w) { 
	"use strict";
	
	// Find vendor prefix, if any
	var vendors = ['ms', 'moz', 'webkit', 'o'];
	for( var i = 0; i < vendors.length && !w.requestAnimationFrame; i++ ) {
		w.requestAnimationFrame = w[vendors[i]+'RequestAnimationFrame'];
	}
	
	// Use requestAnimationFrame if available
	if( w.requestAnimationFrame ) {
		var next = 1, 
			anims = {};
				
		w.setAnimation = function( callback, element ) {
			var current = next++;
			anims[current] = true;
			
			var animate = function() {
				if( !anims[current] ) { return; } // deleted?
				w.requestAnimationFrame( animate, element );
				callback();
			};
			w.requestAnimationFrame( animate, element );
			return current;
		};
		
		w.clearAnimation = function( id ) {
			delete anims[id];
		};
	}
	
	// [set/clear]Interval fallback
	else {
		w.setAnimation = function( callback, element ) {
			return w.setInterval( callback, 1000/60 );
		}
		w.clearAnimation = w.clearInterval;
	}
}(window));