rAF.js

// paulirish, emoller et al. MIT license

window.requestAnimationFrame = window.requestAnimationFrame || function(callback, element){
    var fn, cfn, w = window, lastTime = 0, v, vendors = 'webkit,moz,ms,o'.split(',');
	while(!fn && (v = vendors.shift())){
		fn = w[v+'RequestAnimationFrame'];
		cfn = w[v+'CancelAnimationFrame'] || w[v+'CancelRequestAnimationFrame'];
	};
	w.requestAnimationFrame = fn || function(callback, element){
		var id, currTime = new Date().getTime(), timeToCall = Math.max(0, 16 - (currTime - lastTime));
		id = window.setTimeout(function() { callback(currTime + timeToCall); }, timeToCall);
		lastTime = currTime + timeToCall;
	};
	w.cancelAnimationFrame = cfn || w.clearTimeout;
	fn(callback, element);
};