DIV与JAVASCRIPT问题，请教
请教大家一个问题，只想隐藏DIV ID=a1、a2、a3等没有textarea的DIV，可是现在连div id=n1的也隐藏了啊。
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<p>
</p>
<style type="text/css">
ul {width:100%;height:100%;list-style:none; padding:0px; margin:0px;}
li {float:left; height:60px;text-align:center;line-height:60px; padding-top:5px;}
li.b {border-bottom:1px solid #000;border-right:1px solid #000; width:20%; }
li.zhongjian {border-bottom:1px solid #000; width:59%;border-right:1px solid #000; text-align:left; padding-left:6px; }
li.you {
border-bottom:1px solid #000;
width:20%; margin-top:auto;
}
li.b1 {border-right:1px solid #000; width:20%; }
li.zhongjian1 {width:59%;border-right:1px solid #000; text-align:left; padding-left:6px; }
li.you1 {
width:20%; margin-top:auto;
}
td { font-size: 9pt}
.title { font-size: 10.5pt}
.iwhite {
border-left: 1px solid rgb(255,255,255);
border-right: 1px solid rgb(255,255,255);
border-top: 1px solid rgb(255,255,255);
border-bottom:1px solid rgb(0.0,255);
font-family: "Verdana", "Arial", "Helvetica", "sans-serif";
font-size: 9pt; color: #298583;background:#ffffff; font-weight: normal}
.igray {font-family: "宋体";
font-size: 9pt;
color: #000000;
background:#ffffff;
font-weight: normal;
border-bottom: 0px solid #D7E0EC;
border-top: 0px solid #DADBE3;
border-right: 0px solid #DADBE3;
border-left: 0px solid #DADBE3;
}
.igrby {font-family: "宋体";
font-size: 9pt;
color: #000000;
background:#ffffff;
font-weight: normal;
border-bottom: 0px solid #D7E0EC;
border-top: 0px solid #DADBE3;
border-right: 0px solid #DADBE3;
border-left: 0px solid #DADBE3;
}
.tabborder {
border:1px solid #ffffff;
}
.writetd {
text-align:left;
padding:6px;
}
</style>
<table border="0" cellpadding="0" cellspacing="0" style="border-right-width: 0px; border-top-width: 0px; border-bottom-width: 0px; border-left-width: 0px" width="100%">
<tbody>
<tr>
<td align="middle" height="42" style="border-right-width: 0px; border-top-width: 0px; border-bottom-width: 0px; border-left-width: 0px">
<font size="+1"><strong>员工离职审批单</strong></font></td>
</tr>
</tbody>
</table>
<table align="center" border="1" bordercolor="#666666" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="95%">
<tbody>
<tr>
<td bgcolor="#ffffff" colspan="2" style="text-align: center">
公文标题</td>
<td bgcolor="#ffffff" class="writetd" colspan="6">
<input name="文件标题" size="40" /><span style="color: #8b4513">（例：生产部张三的离职申请）</span></td>
</tr>
<tr>
<td class="writetd" style="text-align: center">
姓名</td>
<td class="writetd">
<input id="3698" name="姓名" size="10" style="width: 70px; height: 18px" /></td>
<td class="writetd" style="text-align: center">
部门</td>
<td class="writetd">
<input id="3699" name="部门" size="10" style="width: 70px; height: 18px" /></td>
<td class="writetd" style="text-align: center">
入职日期</td>
<td class="writetd">
<input id="3700" name="入职日期" size="10" style="width: 70px; height: 18px" /></td>
<td class="writetd" style="text-align: center">
交接日期</td>
<td class="writetd">
<input id="3701" name="交接日期" size="10" style="width: 70px; height: 18px" /></td>
</tr>
<tr>
<td class="writetd" style="text-align: center">
类型</td>
<td class="writetd">
<input id="3697" name="离职类型" size="10" style="width: 70px; height: 18px" /></td>
<td class="writetd" style="text-align: center">
职务</td>
<td class="writetd" style="text-align: justify">
<input id="3704" name="职务" size="10" style="width: 70px; height: 18px" /></td>
<td class="writetd" style="text-align: center">
交接人</td>
<td class="writetd">
<input id="3703" name="交接人" size="10" style="width: 70px; height: 18px" /></td>
<td style="text-align: center">
离职日期</td>
<td class="writetd">
<input id="3702" name="离职日期" size="10" style="width: 70px; height: 18px" /></td>
</tr>
<tr>
<td bgcolor="#ffffff" colspan="2" style="text-align: center" width="100%">
<div id="n1">
<ul>
<li class="b">离职原因</li>
<li class="zhongjian"><input readOnly type="text" class="igray" id="3998" name="fieldstr6" value=""></li>
<li class="you"></li>
</ul>
</div></td>
</tr>
<tr>
<td colspan="8" style="text-align:center">
<div style="clear:both"></div>
<div id="a1">
<ul>
<li class="b">生活更美好1</li>
<li class="zhongjian"><input readOnly type="text" class="igray" id="3998" name="fieldstr6" value=""></li>
<li class="you"> <input readOnly type="text" class="igray" id="3999" name="fieldstr7" value=""></li>
</ul>
</div>
<div style="clear:both"></div>
<div id="a2">
<ul>
<li class="b">生活更美好2</li>
<li class="zhongjian"><textarea readOnly cols="60" id="4381" name="longstr3" rows="3"></textarea readOnly></li>
<li class="you"> <span></span></li>
</ul>
</div>
<div style="clear:both"></div>
<div id="a3">
<ul>
<li class="b">生活更美好3</li>
<li class="zhongjian"><textarea readOnly cols="60" id="4381" name="longstr3" rows="3"></textarea readOnly></li>
<li class="you"> <input readOnly type="text" id="3999" name="fieldstr7" value=""></li>
</ul>
</div>
<div style="clear:both"></div>
<div id="a4">
<ul>
<li class="b">生活更美好4</li>
<li class="zhongjian"><textarea readOnly cols="60" id="4381" name="longstr3" rows="3"></textarea readOnly></li>
<li class="you"> </li>
</ul>
</div>
<div style="clear:both"></div>
<div id="a5">
<ul>
<li class="b">生活更美好5</li>
<li class="zhongjian"><textarea readOnly cols="60" id="4381" name="longstr3" rows="3"></textarea readOnly></li>
<li class="you"> <input readOnly type="text" id="3999" name="fieldstr7" value=""></li>
</ul>
</div>
<div style="clear:both"></div>
<div id="a6">
<ul>
<li class="b1">生活更美好6</li>
<li class="zhongjian1"><textarea readOnly cols="60" id="4381" name="longstr3" rows="3"></textarea readOnly></li>
<li class="you1"> <input readOnly type="text" id="3999" name="fieldstr7" value=""></li>
</ul>
</div>
<div style="clear:both"></div>
</td>
</tr>
<tr>
<td class="writetd" colspan="4" style="text-align: center">
制单人：<input name="提交人" /></td>
<td class="writetd" colspan="4" style="text-align: center">
制单日期：<input name="提交日期" /></td>
</tr>
<tr>
<td class="writetd" colspan="8">
1、人力资源部每月18日、30日办理员工离职手续相关事宜，其他时间不予办理。<br />
2、员工完成工作交接并完成本人离职手续后方可离职。<br />
3、交接单一式三份，人力资源部、移交人及交接人各一份。</td>
</tr>
</tbody>
</table>
<script type="text/javascript">
window.onload=function(){
var a=document.getElementsByTagName("div");
for(i=0;i<a.length;i++)
{
var b=a[i].getElementsByTagName("textarea");
if(b.length==0)
{
a[i].style.display='none';
}
}
}
</script>
[解决办法]
第一步：给你想要判断的div的td给个ID，好精确定位。例如：下面我给了个id为my
<td colspan="8" style="text-align:center" id="my"> <div style="clear:both"></div><div id="a1"> <ul> <li class="b">生活更美好1</li> <li class="zhongjian"><input readOnly type="text" class="igray" id="3998" name="fieldstr6" value=""></li> <li class="you"> <input readOnly type="text" class="igray" id="3999" name="fieldstr7" value=""></li> </ul> </div>
