为什么鼠标滑过li都没加上样式，头痛欲裂~求救大神~~

Question

window.onload=function() {         var oTab=document.getElementById("month_tit");         var oTac=document.getElementById("month_con");         var aH3=oTab.getElementsByTagName("li");         var aDiv=oTac.getElementsByTagName("div");         for(var i=0;i<aH3.length;i++)         {                 aH3[i].id=i;                 aH3[i].onmouseover=function()                 {                         for (var j=0;j<aH3.length;j++)                         {                                 aH3[j].className="";                                 aDiv[j].style.display="none";                         }                         this.className="select";                         aDiv[this.id].style.display="block";                 }         } }

Answer 1

<div class="exam">
<div class="bannerright_top">
<span class="examdate">考试日历</span>
<div class="month" id="month">
<div class="month_tit flexslider" id="month_tit">
<ul class="monthdate slides">
<li class="select"><span>1</span>月</li>
<li><span>11</span>月</li>
<li><span>12</span>月</li>
</ul>
</div>
<div class="month_con" id="month_con">
<div class="mod" style="display:block;" id="mod">
<ul id="div1">
<li>计算机科学与应用<span>12月25日</span></li>
<li>计算机科学与应用<span>12月25日</span></li>
</ul>
</div>
<div class="mod" id="mod" style="display:none;">
<ul id="div1">
<li>计算机科学与应用<span>12月25日</span></li>
<li>计算机科学与应用<span>12月25日</span></li>
</ul>
</div>
</div>
</div>

Answer 2

把你的html也粘出来，不然无从下手啊