In our AJAX QuickBuild event yesterday, Simon Allardice demonstrated for everyone how to access the value of a server control from client-side script. Let me share with you his tip/trick. It is quite simple. Here is the markup of a content page - notice the script tag:
<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" Title="Who Cares?" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
<div>
<asp:Label ID="LabelMessage" Text="In Content control" runat="server"></asp:Label>
</div>
<script type="text/javascript">
alert($get('<%=LabelMessage.ClientID %>').id);
</script>
</asp:Content>
Note the script element contains server code to request the client id of the control. When this page executes, the following alert appears:
Because ASP.NET will alter the ID of a server control based on a variety of reasons, accessing the client id is the best way to get the actual rendered id! Thanks Simon!