js控制fieldset高度

<script language="JavaScript">
<!--
function admin_Size(num,objname)
{
   var obj=document.getElementById(objname);
   if (parseInt(obj.style.height)+num>=50) {
     obj.style.height = parseInt(obj.style.height) + num;
   }
   if (num>0)
   {
     obj.width="90%";
   }
}
//-->
</script>
<fieldset name="ArticleIntro" ID="ArticleIntro" style="width:234px;height:100px;text-align:center;color:deeppink;"><legend style="font-weight:800;">不是太熟悉</legend>就要去学习</fieldset><br>
<a href="javascript:admin_Size(-50,'ArticleIntro')">减小</a>
<a href="javascript:admin_Size(50,'ArticleIntro')">增加</a>