chaping

var lastTime = 0;
var prefixes = 'webkit moz ms o'.split(' '); //各浏览器前缀

var requestAnimationFrame = window.requestAnimationFrame;
var cancelAnimationFrame = window.cancelAnimationFrame;

var prefix;
//通过遍历各浏览器前缀，来得到requestAnimationFrame和cancelAnimationFrame在当前浏览器的实现形式
for( var i = 0; i < prefixes.length; i++ ) {
	if ( requestAnimationFrame && cancelAnimationFrame ) {