/**     * requestAnimationFrame兼容性扩展，两方面工作：     * 1、把各浏览器前缀进行统一     * 2、在浏览器没有requestAnimationFrame方法时将其指向setTimeout方法     * */    (function() {        var lastTime = 0;        var vendors = ["webkit", "moz"];        for (var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {            window.requestAnimationFrame = window[vendors[x] + "RequestAnimationFrame"];            // Webkit中此取消方法的名字变了            window.cancelAnimationFrame = window[vendors[x] + "CancelAnimationFrame"] || window[vendors[x] + "CancelRequestAnimationFrame"];        }        if (!window.requestAnimationFrame) {            window.requestAnimationFrame = function(callback, element) {                var currTime = new Date().getTime();                var timeToCall = Math.max(0, 16.7 - (currTime - lastTime));                var id = window.setTimeout(function() {                    callback(currTime + timeToCall);                }, timeToCall);                lastTime = currTime + timeToCall;                return id;            };        }        if (!window.cancelAnimationFrame) {            window.cancelAnimationFrame = function(id) {                clearTimeout(id);            };        }    }());