兼容的rAF实现

[code] 兼容的rAF

(function() {
    let lastTime = 0;
    // 增加兼容性
    window.requestAnimationFrame = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame
    window.cancelAnimationFrame = window.cancelAnimationFrame || window.webkitCancelAnimationFrame || window.mozCancelAnimationFrame
    // 兜底setTimeout保持代码可行
    if (!window.requestAnimationFrame) {
        window.requestAnimationFrame = function (callback, element) {
            let currTime = new Date().getTime();
            let timeToCall = Math.max(0, 16.7 - (currTime - lastTime));
            let id = window.setTimeout(function () {
                callback(currTime + timeToCall);
            }, timeToCall);
            lastTime = currTime + timeToCall;
            return id;
        };
    }
    if (!window.cancelAnimationFrame) {
        window.cancelAnimationFrame = function (id) {
            clearTimeout(id);
        };
    }
}());