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Asked: 2026-05-29T19:32:41+00:00

I know this is a very common problem. I was trying to get a

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I know this is a very common problem. I was trying to get a “enter key” event to invoke a click on a certain button on the page through javascript. However, I can’t for the life of me fetch a single element by its id or name from my asp.net page.

It is my understanding that this issue is related to where the javascript is located and whether the elements have been rendered by the time the javascript is loaded or something of that nature?

Every time I attempt to use var x = document.getElementById('btn_AddAdmin') I end up with a null value.

My asp.net page has SiteMaster page that it inherits from. I have included a trimmed down version of my asp.net page and the SiteMaster page.

ASP.NET Page:

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master" 
     AutoEventWireup="true" CodeBehind="Admin.aspx.cs" Inherits="HERMES.Admin" %>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<input type="text" id="txt_AddAdmin" runat="server" onkeypress="Populate()" />

Master Page:

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site.master.cs" 
         Inherits="HERMES.SiteMaster" %> 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head runat="server">
    <title></title>
    <link href="./Styles/Site.css" rel="stylesheet" type="text/css" />
    <asp:ContentPlaceHolder ID="HeadContent" runat="server">
    </asp:ContentPlaceHolder>
</head>
<body>
    <form runat="server">
</form>
</body>

Sorry for the formatting, I seem to be doing something wrong…

I have attempted placing the javascript in many different locations — anywhere from the sitemaster page to the top and bottom of my asp.net page. No luck either way.

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1 Answer

  1. Editorial Team
    var x = document.getElementById('<%= btn_AddAdmin.ClientID %>');

    If your button is a Server Control it prepends a naming scheme to the input button so it can be bound back to the appropriate server control during postback. Thus the need to use the ClientID property to retrieve the “rendered id”.

    To learn more visit:

    Google it with Bing:

    • clientid
    • aspnet webforms client side programming
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