很简单：在前边页面加一个按钮，设为隐藏。使用js代码调用该按钮的click事件，以此达到用前台js调用后台c#代码的功效。
前台代码：
default.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
<script type ="text/javascript">
$(function () {
$("#button1").click();
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Button ID = "button1" OnClick = "CSharpVoid" runat = "server" Visible = "false" />
</div>
</form>
</body>
</html>
default.aspx.cs
defaul.aspx.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void CSharpVoid(object sender,EventArgs e) {
string str = "www.baidu.com";
Response.Write(str);
}
}