The suggested approach is add a specific content place holder controls for such scripts to be placed in the web page you are rendering. Take a look at the following master/content page markup:
Master page:
<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site1.master.cs" Inherits="WebApp.PageMethods.Site1" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<asp:ContentPlaceHolder ID="head" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
There is a content place holder head
wherein I must write some js functions trying to access the dropdown list in the other content place holder ContentPlaceHolder1
.
Content page markup:
<%@ Page Title="" Language="C#" MasterPageFile="~/Site1.Master" AutoEventWireup="true" CodeBehind="WebForm3.aspx.cs" Inherits="WebApp.PageMethods.WebForm3" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
<script>
function foo() {
var ddl = document.getElementById('<%= DropDownList1.ClientID %>');
}
</script>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<asp:DropDownList ID="DropDownList1" runat="server"></asp:DropDownList>
</asp:Content>
Here I didn't have to worry so much about trying to access controls nested in ContentPlaceHolderID
.
Alternatively, if you don't have that option/freedom, you can always write something as follows in your master page itself:
var d = document.getElementById('<%= this.ContentPlaceHolder1.FindControl("DropDownList1").ClientID %>');