Using multiple instances of an aspx user control in a aspx page

Question 1

After some searching found a different solution.

http://www.aspsnippets.com/Articles/Issue-JavaScript-in-WebUserControl-not-working-when-used-multiple-times-on-same-page.aspx

Here they append an uniqueID with the javascript name, thereby there is no conflict with the javascripts.

UserControl.CS

protected string uniqueKey;
protected void Page_Load(object sender, EventArgs e)
{
    this.uniqueKey = Guid.NewGuid().ToString("N");
    this.Button1.Attributes["onclick"] = "return DisplayMessage_" + uniqueKey + "();";
}

UserControl.aspx

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="UC_TestCS.ascx.cs" Inherits="UC_TestCS" %>
<script type ="text/javascript">
function DisplayMessage_<%=uniqueKey %>() {
    var message = document.getElementById("<%=TextBox1.ClientID %>").value;
    alert(message);
    return false;
}
</script>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Show Message" />

Question 2

Refer to the similar question in the post

Javascript functions inside ASP.NET User Control

You need to use ClientScriptManager as shown in the example below

 <%@ Page Language="C#"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
  public void Page_Load(Object sender, EventArgs e)
  {
    // Define the name and type of the client scripts on the page.
    String csname1 = "PopupScript";
    String csname2 = "ButtonClickScript";
    Type cstype = this.GetType();

    // Get a ClientScriptManager reference from the Page class.
    ClientScriptManager cs = Page.ClientScript;

    // Check to see if the startup script is already registered.
    if (!cs.IsStartupScriptRegistered(cstype, csname1))
    {
      String cstext1 = "alert('Hello World');";
      cs.RegisterStartupScript(cstype, csname1, cstext1, true);
    }

    // Check to see if the client script is already registered.
    if (!cs.IsClientScriptBlockRegistered(cstype, csname2))
    {
      StringBuilder cstext2 = new StringBuilder();
      cstext2.Append("<script type=\"text/javascript\"> function DoClick() {");
      cstext2.Append("Form1.Message.value='Text from client script.'} </");
      cstext2.Append("script>");
      cs.RegisterClientScriptBlock(cstype, csname2, cstext2.ToString(), false);
    }
  }
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>ClientScriptManager Example</title>
  </head>
  <body>
     <form id="Form1"
         runat="server">
        <input type="text" id="Message" /> <input type="button" value="ClickMe" onclick="DoClick()" />
     </form>
  </body>
</html>