http://www.cnblogs.com/blodfox777/articles/1261303.html
Button有两个点击事件：
onclick 触发服务端事件，脚本为c#或VB.NET
OnClientClick 触发客户端事件，脚本一般为JavaScript，此属性为ASP.NET 2.0新增，1.1之前需要使用添加attribute的方法来添加客户端事件
在点击按钮时，先运行OnClientClick 中的脚本，如果返回值为true，则再运行button_onclick 中的代码, 否则将不会执行该按钮的后台代码
demo:
<!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>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Button ID="Button1" runat="server" Text="Button"
OnClientClick="return confirm('Are u sure?');" onclick="Button1_Click"/>
</div>
</form>
</body>
</html>
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
public partial class Default2 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Button1_Click(object sender, EventArgs e)
{
Response.Write("if you press OK, Button1_Click will be execute");
}
}