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Editorial Team
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Asked: 2026-06-13T04:55:41+00:00

I have a web app in ASP.NET with a C# code behind. The main

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I have a web app in ASP.NET with a C# code behind. The main login page is going to have a sort of touchpad type UI where there are buttons for 0-9 to enter a pin #.

So, I’m new to ASP.NET and to JavaScript both. When these numeric buttons are clicked on the UI, nothing needs to be done on the server side – there shouldn’t be any postback at all. All that needs be done is append a number to a label’s text. I’m trying to figure out how to do that in JavaScript, without the button causing any kind of postback.

To make the example much simpler, let’s just say I have a UI with a single label and single button on the screen, and everytime you click this single button, it should append a 1 to the label’s text. Here’s my .aspx, but when I try to run this, I get a “Object Expected” exception at runtime…

EDIT: I’ve modified my example to include the suggestions made in answers below, and still am having issues. To reproduce, this .aspx code can be copied into the default.aspx of a new VS Web Application project, and run it and click the 1 button; it should append a 1 to the label’s value, but it throws an “Object Expected” exception.

 <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="TestJavascript._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title></title>
</head>
<body>
  <form id="form1" runat="server">
    <div>
      <asp:Table ID="baseTable" runat="server" HorizontalAlign="Center">
        <asp:TableRow ID="labelRow" runat="server" HorizontalAlign="Center" Width="100" Height="30">
          <asp:TableCell ID="labelCell" runat="server" HorizontalAlign="Center" Width="100%" Height="100%" BorderStyle="Solid" BorderWidth="1px">
            <asp:Label ID="inputLbl" runat="server"/>
          </asp:TableCell>
        </asp:TableRow>
        <asp:TableRow ID="buttonRow" runat="server" HorizontalAlign="Center">
          <asp:TableCell ID="buttonCell" runat="server" HorizontalAlign="Center">
            <asp:Button ID="btn1" runat="server" Text="1" Height="70px" Width="70px" OnClientClick="btn1Click()"/>
          </asp:TableCell>
        </asp:TableRow>
      </asp:Table>
    </div>
  </form>
  <script type="txt/javascript">
    void btn1Click()
    {
        document.getElementById('<%= inputLbl.ClientID %>').value += "1";
        return false;
    }
  </script>
</body>
</html>

Any help is much appreciated!

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1 Answer

  1. Editorial Team

    First of all, a variable name should not start with a number, so replace 1Btn with a significative name (btnAppendOne).

    1. Bind the onclick client event to your Button, in your PageLoad method:

      btnAppendOne.Attributes.Add("onclick", "return btnAppendOneClick();");

    2. Use the correct javascript (return false should cancel the postback):

      <script type="text/javascript">
     function btnAppendOneClick()
     {
         var updatedLabel = document.getElementById('<%=inputLbl.ClientID %>');
         updatedLabel.innerHTML = updatedLabel.innerHTML + "1";
         return false;
     }
</script>
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