parentElement,实现背景图片切换

Question

asp.net 中通过全局变量控制td的背景，通过点击服务器控件LINKBUTTON 相应客户端的JS 事项切换图片的效果，可是我写的JS提示不对，想不明白 望高手指点 
   <td>
    |-<div>
      |-<LinkButton><script>
    function change(o) 
    { 
    var hwj = document.getElementById(o).offsetParent.offsetParent.style.background;
    var tdd=document.getElementById(o).offsetParent.offsetParent.id;   
    document.getElementById(tdd).style.background=hwj=="img/kj_lbg2.gif"?<%bg="img/kj_lbg.gif";%><%=bg%>:<%bg="img/kj_lbg2.gif";%><%=bg%>; 
    } 
</script>
     <asp:DataList ID="dlLv2Pro" runat="server" RepeatColumns=1 OnItemCommand="dlLv2Pro_ItemCommand" Width="1px">
           <ItemTemplate> 
            <table width="30" border="0" cellpadding="0" cellspacing="0">
             <tr> 
               <td width="30" id="<%#Eval("autoid")%>" align="center" background='<%=bg%>' class="tnt"  >
               <div class="tnt2" style="margin:auto; padding-bottom:3px; padding-top:3px; padding-right:6px; text-align:center; ">
               <asp:LinkButton ID="lkLinkbtn" OnClientClick="change(this)"  runat="server" style=" letter-spacing:2pt; WRITING-MODE: tb-rl; " CommandName="sort" CommandArgument=<%#Eval("autoid")%>><%#Eval("prolvname2")%></asp:LinkButton>
               </div>
               </td>
             </tr> 
             </table>
           </ItemTemplate>
         </asp:DataList>  
</td>