js下拉菜单问题

Question

script type="text/javascript">

         function showsubmenu(h3){

  var  submenu=getElementsByClass("shopClass_show")[0];

  submenu.style.display="block";

 }

  </script>

<div class="shopClass" style="float:left">

  <h3 onmousover="showsubmenu()" onmousout="hide">全部商品分类<i></i></h3>

                     <div class="shopClass_show">

        <dl class="shopClass_item">

       <dt>

 <a href="#" class="b">手机</a> <a href="#">数码</a> <a href="#" class="contract">合约机</a>

</dt> 

<dd>

<a href="#">荣耀3X</a> <a href="#">单反</a> <a href="#">智能设备</a>

</dd>

</dl>