保持动画的继续

var requestAnimationFrame = window.requestAnimationFrame 
    ||window.mozRequestAnimationFrame
    || window.webkitRequestAnimationFrame 
    || window.msRequestAnimationFrame;

	var cancelFrame = window.cancelRequestAnimationFrame ||
			window.webkitCancelAnimationFrame ||
			window.webkitCancelRequestAnimationFrame ||
			window.mozCancelRequestAnimationFrame ||
			window.oCancelRequestAnimationFrame ||
			window.msCancelRequestAnimationFrame ||
			clearTimeout;