利用弹性运动的原理做弹性菜单

主要是速度以及临界条件的处理
弹性运动的函数

function startMove(obj,target) {
    clearInterval(obj.timer);
    var speed=0;
    obj.timer = setInterval(function() {
        speed += (target - obj.offsetLeft) / 6;
        //类似于摩擦系数
        speed *= 0.75;
        if(Math.abs(speed) < 1 && Math.abs(target - obj.offsetLeft) < 1) {
            clearInterval(obj.timer);
            obj.style.left = target;
            speed = 0;
        } else {
            obj.style.left = obj.offsetLeft + speed + 'px';
        }
//        console.log(obj.offsetLeft + '/' + speed);
    }, 30);
}


<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <link rel="stylesheet" type="text/css" href="../css/public.css"/>
        <style>
            #list{width: 450px;height: 40px;margin: 100px auto;position: relative;}
            #list li.box{width: 100px;height: 40px;line-height: 40px;text-align: center;border: 1px solid #999;float: left;margin-right: 10px;background: red;}
            #mark{width: 101px;height: 42px;background: green;position: absolute;top: 0;left: 0;}
        </style>
        <script type="text/javascript" src="../js/rainbow.js"></script>
        <script type="text/javascript">
            window.onload=function(){
                var oUl=document.getElementById("list");
                var oMark=document.getElementById("mark");
                var aBox=getElementsByClassName(document,'li','box');
                var timer=null;
                for(var i=0;i<aBox.length;i++){
                    aBox[i].onmouseover=function(){
                        clearTimeout(timer);
                        startMove(oMark,this.offsetLeft);
                    };
                    aBox[i].onmouseout=function(){
                        timer=setTimeout(function(){
                            startMove(oMark,0);
                        },100);
                    }
                }
                oMark.onmouseover=function(){
                    clearTimeout(timer);
                };
                oMark.onmouseout=function(){
                    startMove(oMark,0);
                }
            }
        </script>
    </head>
    <body>
        <ul id="list">
            <li id="mark"></li>
            <li class="box">首页</li>
            <li class="box">论坛</li>
            <li class="box">体育</li>
            <li class="box">新闻</li>
        </ul>
    </body>
</html>