显示TEXTAREA文本框剩余字数

<script type="text/javascript" language="javascript">         function   textCounter(field,   maxlimit)       {           if   (document.getElementById(field).value.length   >   maxlimit)         {        document.getElementById(field).value   =   document.getElementById(field).value.substring(0,maxlimit);          }        else           {        document.getElementById("remLen").value   =   maxlimit   -   document.getElementById(field).value.length;       }       }     </script> 

 

 

<form runat="server" id="writemsgtxt"><table width="100%" border="0" cellspacing="0" cellpadding="0">                      <tr>                        <td height="22" align="left">&nbsp;你還可以留言                          <input readonly type="text" id="remLen" runat="server" size="4" maxlength="3" value="500" class="input1" />                          字                        </td>                      </tr>                                                  <tr>                        <td align="left">                        <asp:TextBox ID="content" runat="server" CssClass="input2" Rows="8" Columns="50" TextMode="MultiLine" onkeyup="textCounter('content',500)"></asp:TextBox>                        </td>                      </tr></table></form>