用requestAnimationFrame实现的一个动画效果

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在看Scott老师的node视频中，讲到一个动画效果，我用requestAnimationFrame实现了这个效果。
代码
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>应用requestAnimationFrame做一个动画效果</title>
    <style type="text/css">
        .ball{
            width: 20px;
            height: 20px;
            border-radius: 50%;
        }
        .red{
            background-color: red;
        }
        .green{
            background-color: green;
        }
        .blue{
            background-color: blue;
        }
    </style>
</head>
<body>
    <p>在看node教程，老师介绍promise时，用seTtimeout实现了一个动画效果，用requestAnimationFrame练练手</p>
    <div>
        <p class="ball red" style="margin-left:0px;"></p>
        <p class="ball green" style="margin-left:0px;"></p>
        <p class="ball blue" style="margin-left:0px;"></p>
    </div>
    <script type="text/javascript">
        var red = document.querySelector(".red");
        var green = document.querySelector(".green");
        var blue = document.querySelector(".blue");
        window.requestAnimationFrame = window.requestAnimationFrame  window.mozRequestAnimationFrame  window.webkitRequestAnimationFrame  window.msRequestAnimationFrame;

        ani(red,100,function(){
            ani(green,200,function(){
                ani(blue,150,function(){
                    ani(red,150);
                    ani(green,150)
                })
            })
        })
        function ani(node,to,callback){
            var marginLeft = parseInt(node.style.marginLeft);
            requestAnimationFrame(function(){
                if (marginLeft == to) {
                    callback && callback()
                }else{
                    if (marginLeft < to) {
                        marginLeft++
                    }else if(marginLeft>to){
                        marginLeft--
                    }
                    node.style.marginLeft = marginLeft + "px";
                    ani(node,to,callback)
                }
            })  
        }
    </script>
</body>
</html>