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Editorial Team
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Asked: 2026-05-11T21:38:09+00:00

When you assign something an ID in asp.net such as: <asp:Label runat=server ID=mylabel Text=some

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When you assign something an ID in asp.net such as:

<asp:Label runat="server" ID="mylabel" Text="some text"></asp:Label>

The code behind ID you use to reference that object is mylabel.

However after the site has compiled and is running the ID in the HTML changes to something a bit more abscure 

<asp:Label runat="server" ID="ct100_blahblah_what_mylabel" Text="some text"></asp:Label>

And I cannot (don’t know how) to reliably predict what it will be to select it with javascript.

Is there a way to ask the server what the ID for that label is at any given moment?

What are some keywords could use to find out more about this phenomenon?

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1 Answer

  1. Editorial Team

    You need the ClientID property. This contains the generated id of the control at runtime. You could emit some JavaScript in the code behind that sets the client id of your control to a JavaScript variable so you can reference it.

    EDIT: added example

    The following will find the label using the ClientID and then update its text.

        <html>
    <body>
        <asp:Label runat="server" ID="mylabel" Text="some text"></asp:Label>

        <script language="javascript">
            var mylabelID = "<%= mylabel.ClientID %>";
            var label = document.getElementById(mylabelID);
            label.innerHTML += " changed";
        </script>
    </body>
    </html>
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