RequestAnimationFrame.js

/**
 * Provides requestAnimationFrame in a cross browser way.
 * @author paulirish / http://paulirish.com/
 */

if ( !window.requestAnimationFrame ) {
	var pollFocus;
	window.requestAnimationFrame = ( function() {

		return window.webkitRequestAnimationFrame ||
		window.mozRequestAnimationFrame ||
		window.oRequestAnimationFrame ||
		window.msRequestAnimationFrame ||
		function( /* function FrameRequestCallback */ callback, /* DOMElement Element */ element ) {
		  // Use document hasFocus to only call animation on focus
		  if("hasFocus" in document && document.hasFocus()) {
                      window.setTimeout(callback, 1000 / 60);
		      clearInterval(pollFocus);
                  } else if("hasFocus" in document && !document.hasFocus()) {
                      // Poll for refocus less CPU intensive?
		      pollFocus = window.setInterval(hasFocus,500);
                  } else {
                      // No hasFocus support fallback to timeout
                      window.setTimeout(callback, 1000 / 60);
		  }  
		};

	} )();

	function hasFocus() {
	    if(document.hasFocus()) {
	        // Document has focus start animation again
	    }
	}
}