<table width="100%" border="0" cellspacing="0" cellpadding="0">
  <tr>
    <td>序号</td>
    <td>列名1</td>
    <td>列名2</td>
    <td>列名3</td>
    <td>列名4</td>
    <td>列名5</td>
    <td>
      <input type="button" name="button" id="button" value="添加"  onclick="addtablerow();"/>
   </td>
  </tr>
  <tr>
    <td colspan="7" id="adddiv">
    <div></div>
     <div></div>
      <div></div>
       <div></div>
    
    </td>
  </tr>
</table>
我想取id=“adddiv” 的td下面 有多少个div  怎么得到啊