Passing ASP.NET label id to Javascript

Question

I can get the Label value to change when I use the following code

  document.getElementById('<%=lblDropdownValue.ClientID %>').innerHTML =     ddl.value;

But I would like to pass it as a parameter as shown below, but it does not seem to work.

<table>
    <tbody>
        <tr>
            <td>
              <asp:DropDownList id="ddlProducts" runat="server" 
           onclick="myfunction(this,'<%=lblDropdownValue.ClientID %> "')">

                <asp:ListItem Selected="True" Value="-1"> Please Select </asp:ListItem>
                <asp:ListItem Value="Car"> BMW </asp:ListItem>
                <asp:ListItem Value="Music"> MP3 </asp:ListItem>

             </asp:DropDownList>

           </td>
           <td>
               <asp:Label Text="" id="lblDropdownValue" runat="server"/>
           </td><td></td>
       </tr>

   </tbody>

</table>
</div>
</form>
<script>
   function myfunction(ddl, lblText)
   {
      document.getElementById("'"+lblText+"'").innerHTML = ddl.value;          
   }
</script>

Wiktor Zychla · Accepted Answer · 2015-02-11 22:08:47Z

1

Put this in the code behind:

public void Page_Load( ... ) {

    ddlProducts.Attributes["onclick"] = "myfunction(...)";

}

and remove the onclick from the ASPX.

The reason for this is that you want the onclick to be attached at the client side. What you now have is an attribute that is evaluated server side and thus it doesn't make it properly to the client.

answered Feb 11, 2015 at 22:08

Wiktor Zychla

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1 Comment

sw2020 Over a year ago

Dziękuję Wiktor Zychla

sw2020 · Accepted Answer · 2015-02-11 22:59:52Z

1

In the code behind I added

   protected void Page_Load(object sender, EventArgs e)
        {
            ddlProducts.Attributes["onclick"] = "myfunction(this,"+lblDropdownValue.ClientID +");";

        }

And Changed the JavaScript to

 <script>
        function myfunction(ddl, lblText)
        {            
           lblText.innerHTML
            = ddl.value;          
        }
    </script>

answered Feb 11, 2015 at 22:59

sw2020

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