javascript获取深层控件

Question

<asp:UpdatePanel id="UpdatePanel1" runat="server">
  <contenttemplate>
    <cc1:TabContainer id="TabContainer1" runat="server"> 
     <cc1:TabPanel runat="server" ID="TabPanel1" Headertext="TabPanel1">
        <ContentTemplate>
          <table id="table1">
            <tbody id="tbody1">
              <tr id="tr1">
                 <td id="td1"></td>
                 <td id="td2">
                    <inpt id="File1" onchange="checkData()" type="file"/>
                 </td>
                 <td id="td3">
                    <IMG id="img" src="" />
                 </td>              
               </tr>
            </tbody>
          </table>
        </ContentTemplate>
     </cc1:tabPanel>
    <cc1:TabContainer>
  </contenttemplate>
</asp:UpdatePanel><script>
function checkData()
{   
    var fileName=document.getElementById("File1").value;  //这是没加table时引用的file1,上面我加了table这句话该怎么写。。          alert(fileName);
     if(fileName=="")
     return;
    var exName=fileName.substr(fileName.lastIndexOf(".")+1).toUpperCase()
    alert(exName)
    if(exName=="JPG"||exName=="BMP"||exName=="GIF")
    {
    document.getElementById("img").src=fileName
    }
    else
    {
     alert("请选择正确的图片文件")
     document.getElementById("File1").value=""
    } 
    
}
</script>

Answer 1

不是只有一个File1吗，不用改吧

Answer 2

                <td id="td2"> 
                    <inpt id="File1" onchange="checkData(this)" type="file"/> 
                </td> 
                <td id="td3"> 
                    <IMG id="img" src="" /> 
                </td>           function checkData(obj) 
{   
    var fileName=obj.value;  
    if(fileName=="") 
    return; 
    var exName=fileName.substr(fileName.lastIndexOf(".")+1).toUpperCase() 
    alert(exName) 
    if(exName=="JPG"||exName=="BMP"||exName=="GIF") 
    { 
     //得到img
     var objparent=obj.parentNode.parentNode;
     var img=objparent.getElementsByTagName('img')[0];
     img.src=fileName 
    } 
    else 
    { 
    alert("请选择正确的图片文件") 
    obj.value="" 
    } 
    
} 

Answer 3

有ID应该都可以读到
或者document.get****().get*****().get****()