Untitled

Dynamic control ID generation of ContentPage
<pages clientIDMode="Static"></pages>

//ctl00$Cntnt$Button1 name works but its dynamically created
       if (ScriptManager1.AsyncPostBackSourceElementID == "Button1")
        {
            Label1.Text = "Async PostBack occured @ " + DateTime.Now.ToLongTimeString();
        }

<asp:Button ID="Button1" runat="server" Text="Refresh me" onclick="Button1_Click" />

<input type="submit" name="ctl00$Cntnt$Button1" value="Refresh me" id="Button1" />

if (ScriptManager1.AsyncPostBackSourceElementID == Button1.UniqueID)
{
    //do whatever
}

<asp:Panel ID="Panel1" runat="server">
    <asp:Label ID="Label1" runat="server" />
</asp:Panel>

<span id="ctl00_Panel1_Label1"></span>

var labelText = Label1.Text;

var labelText = document.getElementById("<%=Label1.ClientID%>").innerText;