function count(){
    var oul = document.getElementById("ul1");
    var ali = oul.getElementsByTagName("li");
    var odiv = document.getElementById("tab-list");
    var adiv = odiv.getElementsByTagName("div");
    for(var i=0;i<ali.length;i++){
        ali[i].index=i;
        ali[i].onmouseover=function() {
            for(var i=0;i<ali.length;i++){
                ali[i].className="";
            }
            this.className="active";
            for(var j=0;j<adiv.length;j++){
                adiv[j].className="hide";
            }
            adiv[this.index].className="show";
        }
    }
}

这样是实现不了的，要加window.onload 才行，为什么