RAF也即是requestAnimationFrame，之前的动画都是基于setTimeout写的，所以为了性能方面的考虑，开始使用requestAnimationFrame写动画。
function animation(obj, data) {
if (obj.timer) {
window.cancelAnimationFrame(obj.timer)
}
obj.timer = window.requestAnimationFrame(function () {
for (var i in data) {
var current=parseInt(obj.style[i]);
var target=parseInt(data[i]);
var speed=(target-current)/8;
speed=speed>0?Math.ceil(speed):Math.floor(speed);
if(current!=target){
obj.style[i]=current+speed+"px";
obj.timer=window.requestAnimationFrame(arguments.callee);
}
}
})
}