JS如何写栏目栏目伸缩?

<foreach name="list" item="v">
     <tr pid="{$v.parent_id}" cid="{$v.cat_id}">
         <td class="left">
           span class="on" style="margin-left:{$v.count}em"></span>
           {$v.cat_name}
          </td>  
          <td>1</td> <span></span><td><img src='__PUBLIC__/images/<if condition="$v.is_delete eq 0">no<else />yes</if>.gif'/></td>
         <td><span><a href="__URL__/addSubCate/cat_id/{$v.cat_id}" target="right">添加子栏目</a><span><span><a href="__URL__/cateSave/cat_id/{$v.cat_id}" target="right">栏目编辑</a><span><span><a href="__URL__/cateDelete/cat_id/{$v.cat_id}">删除栏目</a><span><span><a href="__URL__/cate_remove/cat_id/{$v.cat_id}" target="right">移动栏目</a><span></td>
                        </tr>     
              </foreach>