我正在尝试将选定的下拉项目的值打印到标签中，而无需通过JavaScript回发页面。我尝试按照以下方式将我的JavaScript文件链接到我的主页，但是它不起作用。我在下面包括了母版页和内容页以及我的JavaScript文件。我也必须将JavaScript文件链接到内容页面吗？
master page
<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="MyMaster.master.cs" Inherits="CodingTest2.MyMaster" %>
<!DOCTYPE html>
<html>
<head runat="server">
<title>UHCL</title>
<script src="JavaScript.js"></script>
<asp:ContentPlaceHolder ID="ContentPlaceHolderHead" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<asp:Image ID="Image1" runat="server" ImageUrl="~/Images/uhclbanner.jpg" Height="154px" Width="950px"/>
<br />
<br />
<asp:Menu ID="Menu1" runat="server" Orientation="Horizontal" StaticMenuItemStyle-ItemSpacing="50px">
<StaticMenuItemStyle BorderColor="Green" BorderStyle="Solid" BorderWidth="2px" HorizontalPadding="20px"/>
<Items>
<asp:MenuItem NavigateUrl="~/ComputingStudents.aspx" Text="Computing Students" Value="Computing Students"></asp:MenuItem>
<asp:MenuItem NavigateUrl="~/CourseHistory.aspx" Text="Course History" Value="Course History"></asp:MenuItem>
</Items>
</asp:Menu>
<br />
<br />
<div>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
content page
<%@ Page Title="" Language="C#" MasterPageFile="~/MyMaster.Master" AutoEventWireup="true" CodeBehind="CourseHistory.aspx.cs" Inherits="CodingTest2.CourseHistory" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolderHead" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<asp:DropDownList ID="DropDownStuID" runat="server" DataSourceID="SqlDataSourceStuIDs" DataTextField="stuid" DataValueField="stuid" onchange="ddlSelectID(this)">
</asp:DropDownList>
<br />
<asp:SqlDataSource ID="SqlDataSourceStuIDs" runat="server" ConnectionString="<%$ ConnectionStrings:c432018fa01g1ConnectionString %>" SelectCommand="SELECT stuid from STUDENT WHERE major='CSC' OR
major='CIS';"></asp:SqlDataSource>
<br />
<asp:ListBox ID="ListBoxCourses" runat="server"></asp:ListBox>
<br />
<asp:Label ID="lblCourses" runat="server"></asp:Label>
<br />
<br />
<asp:Label ID="lblErrorMessage" runat="server" ForeColor="Red"></asp:Label>
<br />
</asp:Content>
JavaScript file
function ddlSelectID(ddl) {
var lbl = document.getElementById('lblCourses');
lbl.innerText = ddl.value;
}
function ddlSelectID() {
var ddlReport = document.getElementById("<%=DropDownStuID.ClientID%>");
var lbl = document.getElementById('<%=lblCourses.ClientID%>');
lbl.innerText = ddlReport.options[ddlReport.selectedIndex].value;
}
1）此javascript函数需要在您的页面上调用。通常，这将在客户端上单击按钮时发生。 （OnClientClick方法）或更改下拉列表中的项目时绑定此函数。2）如上更改您的JavaScript函数。