Question

 <!-- requestAnim shim layer by Paul Irish -->
  window.requestAnimFrame = (function(){
    return  window.requestAnimationFrame     ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame  ||
        window.oRequestAnimationFrame    ||
        window.msRequestAnimationFrame   ||
        function(/* function */ callback, /* DOMElement */ element){
        window.setTimeout(callback, 1000 / 60);
        };
  })();

// example code from mr doob : http://mrdoob.com/lab/javascript/requestanimationframe/
var canvas, context, toggle;

init();
animate();

function init() {
  canvas = document.createElement( 'canvas' );
  canvas.width = 512;
  canvas.height = 512;
  context = canvas.getContext( '2d' );
  document.body.appendChild( canvas );
}

function animate() {
  requestAnimFrame( animate );
  draw();
}

function draw() {
  var time = new Date().getTime() * 0.002;
  var x = Math.sin( time ) * 192 + 256;
  var y = Math.cos( time * 0.9 ) * 192 + 256;
  toggle = !toggle;
  context.fillStyle = toggle ? 'rgb(200,200,20)' :  'rgb(20,20,200)';
  context.beginPath();
  context.arc( x, y, 10, 0, Math.PI * 2, true );
  context.closePath();
  context.fill();
}