Javascript in a user control doesnt fire when partial postback occurs in .NET

Question

I am trying to understand a bit about partial postbacks using updatepanels and while lots of things are stumping me, this one has me baffled.

I am using tabs inside of a UpdatePanel and becuase this is an data entry application, I am putting the content into user controls, so each tab has its own user control. In addition, I am adding custom javascript to each of the user controls to handle specific client side things for the stuff in that control.

In doing this though I have noticed that the javascript in the user control does not fire on partial page postbacks.

To simulate this I created a very simple app (using Master Pages with ScriptManager control on the master page) in VS2010.

The content panel of the default page has the following

<asp:UpdatePanel runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true">
<ContentTemplate>
   <asp:Button runat="server" ID="Button1" Text="Partial postback" />
   <br />
   <asp:Panel runat="server" ID="panel"></asp:Panel>
</ContentTemplate>
</asp:UpdatePanel>

Then I created a user control and simply added some plain text and a javascript alert

<%@ Control Language="vb" AutoEventWireup="false" CodeBehind="UC1.ascx.vb" Inherits="TestWebApp_VB.UC1" %>
This is user control 1
<script> alert('control 1'); </script>

Then in the page load event of the Content page, I load the control into the panel.

   Panel.Controls.Add(LoadControl("UC1.ascx"))

In addition on the click handler of the button I also load the control (or a different control when toggling, as described further in)

Button_Click
 Panel.Controls.Clear()
 Panel.Controls.Add(LoadControl("SomeControl.ascx"))

So when the page is first loaded the alert fires, however when you click the button and the page is partially posted back, the alert never fires.

I took this a step forward and created a second user control and had the button toggle loading the controls and also added a normal button outside the UpdatePanel. Any time I did the full postback the javascript in the loaded user control fires, but it never fires on the partial postbacks.

I then went one step forward and moved my javascript in the controls into a function so I could call the function from the PageRequestManager, or from document.ready.

So now my two controls contain this script (with the alert containing a different message for each control)

<script type="text/javascript">
  function userLoad() {
    alert("Identify control");
  }
</script>

And thusly I added this to the end of my content panel

<script type="text/javascript">
   var prm = Sys.WebForms.PageRequestManager.getInstance().add_endRequest(userLoad);
</script>

Well now the javascript fires on every partial postback, however it fires the javascript for the control that last loaded by a full postback.

Example:

1. Page intially loads UserControl1 - the alert for UserControl1 fires (not shown here - the userLoad function is being called in jquery document.ready)
   
2. User clicks button - which should load UserControl2
   
3. UserControl2 is loaded on the screen, but the alert for UserControl1 fires
   

A bit wordy, apologies for that, I found no easy way to explain this.

---Edit----

One of the things I have tried, working with Scotts suggestions. Keep the javascript for each control in a seperate file and put all of it into a function named something like function UC1Load() {} (maybe sticking a namespace around it, if I am feeling frisky), add a reference to the script file in the content page via a

<script src='UC1.js'> 

then register startup script to call this function

 ScriptManager.RegisterStartupScript(ctrl, ctrl.GetType(), "UserJS", "UC1Load()", True)

The biggest problem with this is that I am now having to download a bunch of script that wont ever be used, which is why I was putting the script in the user controls in the first place.

Answer 1

Ok, after creating my own test website and tinkering around, here's what I got to work:

TestControl1

<%@ Control Language="C#" 
            AutoEventWireup="true" 
            CodeFile="TestControl1.ascx.cs" 
            Inherits="Controls_TestControl1" %>

This is Test Control 1

TestControl2

<%@ Control Language="C#" 
            AutoEventWireup="true" 
            CodeFile="TestControl2.ascx.cs" 
            Inherits="Controls_TestControl2" %>

This is Test Control 2

10049777.aspx

<%@ Page Language="C#" 
         MasterPageFile="~/Site.master" 
         AutoEventWireup="true" 
         CodeFile="10049777.aspx.cs" 
         Inherits="_10049777" %>

<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="Server" />
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="Server">
    <asp:UpdatePanel ID="UpdatePanel1" runat="server" 
        UpdateMode="Conditional" 
        ChildrenAsTriggers="true">
        <ContentTemplate>
            <asp:Button ID="Button1" runat="server"
                Text="Partial postback" 
                OnClick="Button1_Click" />
            <br /><br />
            <asp:Panel runat="server" ID="Panel1" />
        </ContentTemplate>
    </asp:UpdatePanel>
</asp:Content>

10049777.aspx.cs

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        var TestControl1 = LoadControl("Controls\\TestControl1.ascx");

        Panel1.Controls.Add(TestControl1);
        ScriptManager.RegisterStartupScript(TestControl1, 
                                            TestControl1.GetType(), 
                                            "TestControl1Script", 
                                            "alert(\"control 1\");", 
                                            true);
    }
}

protected void Button1_Click(object sender, EventArgs e)
{
    var TestControl2 = LoadControl("Controls\\TestControl2.ascx");

    Panel1.Controls.Clear();
    Panel1.Controls.Add(TestControl2);

    ScriptManager.RegisterStartupScript(TestControl2, 
                                        TestControl2.GetType(), 
                                        "TestControl2Script", 
                                        "alert(\"control 2\");", 
                                        true);
}