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>