window.requestAnimFrame = (function(){

  return  window.requestAnimationFrame       ||

          window.webkitRequestAnimationFrame ||

          window.mozRequestAnimationFrame    ||

          function( callback ){

            window.setTimeout(callback, 1000 / 60);

          };

})();

(function() {

    var lastTime = 0;

    var vendors = ['webkit', 'moz'];

    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {

        window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];

        window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] ||    // Webkit中此取消方法的名字变了

                                      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);

        };

    }

}());