关于使用了fckeditor我在页面对textarea进行非空验证。。。

<%@ page language="java"  contentType="text/html;charset=GBK" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>回贴页面 ...</title>
<meta http-equiv="content-type" content="text/html; charset=GBK">
<link rel="stylesheet" type="text/css" href="images/style.css" title="Integrated Styles">
<script language="JavaScript" type="text/javascript" src="images/global.js"></script>
<script type = "text/javascript" src = "ckeditor/ckeditor.js" > </script> 
<script type="text/javascript">
    function checkForm()
    {
    if(document.replyForm.content.value=="")
    {
      alert("请输入要回帖的内容");
      return;
    }
     else 
     document.replyForm.submit();
    }
</script>
<link rel="alternate" type="application/rss+xml" title="RSS" href="http://bbs.chinajavaworld.com/rss/rssmessages.jspa?threadID=744236">
</head>
<body>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
  <tbody>
    <tr>
      <td width="40%"><img src="images/header-stretch.gif" alt="" border="0" height="57" width="100%">
      </td>
      <td width="1%"><img src="images/header-right.gif" alt="" height="57" border="0"></td>
    </tr>
  </tbody>
</table>
<br>
<div id="jive-flatpage">
  <table border="0" cellpadding="0" cellspacing="0" width="100%">
    <tbody>
      <tr valign="top">
        <td width="99%"><p class="jive-breadcrumbs"> <a href="article.jsp">首页</a> &#187; <a href="http://bbs.chinajavaworld.com/forumindex.jspa?categoryID=1">ChinaJavaWorld技术论坛|Java世界_中文论坛</a> &#187; <a href="http://bbs.chinajavaworld.com/category.jspa?categoryID=2">Java 2 Platform, Standard Edition (J2SE)</a> &#187; <a href="http://bbs.chinajavaworld.com/forum.jspa?forumID=20&amp;start=0">Java语言*初级版</a> </p>
          <p class="jive-page-title"> 主题: reply </p></td>
        <td width="1%"><div class="jive-accountbox"></div></td>
      </tr>
    </tbody>
  </table>
  <div class="jive-buttons">
    <table summary="Buttons" border="0" cellpadding="0" cellspacing="0">
      <tbody>
        <tr>
          <td class="jive-icon"><a href="http://bbs.chinajavaworld.com/post%21reply.jspa?threadID=744236"><img src="images/reply-16x16.gif" alt="回复本主题" border="0" height="16" width="16"></a></td>
          <td class="jive-icon-label"><a id="jive-reply-thread" href="">回复本主题</a> </td>
        </tr>
      </tbody>
    </table>
  </div>
  <br>
  <table border="0" cellpadding="0" cellspacing="0" width="930" height="61">
    <tbody>
      <tr valign="top">
        <td width="99%"><div id="jive-message-holder">
            <div class="jive-message-list">
              <div class="jive-table">
                 <form action="replytopic.do?rtid=${topic.tid }" method="post" name="replyForm" >
                 标题：<input type="text" name="title" size="30" value="${topic.ttopic }" readonly="true"><br>
                 内容：<textarea name="content" rows="15" cols="80"></textarea>
                  <script type = "text/javascript" >  
                          CKEDITOR.replace( 'content' );  
                        </script>  
                
                 <br>
                 <p align="center">
                 <input type="button" value="回复" onclick="checkForm()"/>
                 </form>
                
                </div>
              </div>
            </div>
            <div class="jive-message-list-footer">
              <table border="0" cellpadding="0" cellspacing="0" width="100%">
                <tbody>
                  <tr>
                    <td nowrap="nowrap" width="1%"><br><br></td>
                    <td align="center" width="98%"><table border="0" cellpadding="0" cellspacing="0">
                        <tbody>
                          <tr>
                            <td><a href="article.jsp"><img src="images/arrow-left-16x16.gif" alt="返回到主题列表" border="0" height="16" hspace="6" width="16"></a> </td>
                            <td><a href="article.jsp">返回到主题列表</a> </td>
                          </tr>
                        </tbody>
                      </table></td>
                    <td nowrap="nowrap" width="1%">&nbsp;</td>
                  </tr>
                </tbody>
              </table>
            </div>
          </td>
        <td width="1%">&nbsp;</td>
      </tr>
    </tbody>
  </table>
</div>
</body>
</html>
  我在客房端使用document.replyForm.content.value==""验证不了非空啊，
明天要交项目啊，急.......