Avoid numbers in Textbox using ASP.NET AJAX

An old question which was recently asked for an interview.

How can you prevent numbers from being entered into a Textbox, using Microsoft ASP.NET AJAX Framework. Thinking about UpdatePanel’s? Be clever, I have some client-side codes, using the framework itself.

[Client-Side]

   1: <script type="text/javascript">

   2:     function pageLoad() {

   3:         var tbox = $get("Text1");

   4:         $addHandler(tbox, 'keypress', text1_keypress);

   5:     }

   6:  

   7:     function text1_keypress(e) {

   8:         var code = e.charCode;

   9:         if (code >= 48 && code <= 57)

  10:             e.preventDefault();

  11:     }

  12:  

  13:     function pageUnload() {

  14:         var tbox = $get("Text1");

  15:         $removeHandler(tbox, 'keypress', text1_keypress);

  16:     }

  17: </script>

[Markup-Code]

   1: <form id="form1" runat="server">

   2: <asp:ScriptManager ID="ScriptManager1" runat="server">

   3: </asp:ScriptManager>

   4: <div>

   5:     Enter text value:

   6:     <input id="Text1" type="text" />

   7: </div>

   8: </form>

Thanks.