window.onload=function () {

        var oUl1=document.getElementById('ul1');

        var ali=oUl1.getElementsByTagName('li');   

        var odiv=document.getElementById("tab-list");

        var adiv=odiv.getElementsByTagName('div');

        for(var i=0;i<ali.length;i++){

            ali[i].onmouseover=function(){this.className="active";adiv[i].className="";}//报错Uncaught TypeError: Cannot set property 'className' of undefined   为什么必须用先定义   ali[i].index=i;   再使用  adiv[this.index].className=""  才可以

            ali[i].onmouseout=function(){this.className="";adiv[i].className="hide"}//报错Uncaught TypeError: Cannot set property 'className' of undefined 

        }

    }