requestAnimationFrame兼容写法

requestAnimationFrame.js

window.requestAnimationFrame =
    window.__requestAnimationFrame ||
        window.requestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        window.oRequestAnimationFrame ||
        window.msRequestAnimationFrame ||
        (function () {
            return function (callback, element) {
                var lastTime = element.__lastTime;
                if (lastTime === undefined) {
                    lastTime = 0;
                }
                var currTime = Date.now();
                var timeToCall = Math.max(1, 33 - (currTime - lastTime));
                window.setTimeout(callback, timeToCall);
                element.__lastTime = currTime + timeToCall;
            };
        })();