winform调用javascript

<html>
     <head>
          <title></title>
          <script type="text/javascript">
          function ShowMessage(message)
          {
               alert(message);
          }
          function ShowWinFormsMessage() {
               var msg = document.getElementById('txtMessage').value;
               return window.external.ShowMessage(msg);
          }
          </script>
     </head>
     <body>
          <input type="text" id="txtMessage" />
          <input type="button" value="Show Message" onclick="ShowWinFormsMessage()" />
     </body>
</html>

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace WebBrowserJavaScriptExample
{
    public partial class frmMain : Form
    {
        public frmMain()
        {
            InitializeComponent();
            webBrowser1.ObjectForScripting = new ScriptManager(this);
        }
        private void btnShowMessage_Click(object sender, EventArgs e)
        {
            object[] o = new object[1];
            o[0]=txtMessage.Text;
            object result = this.webBrowser1.Document.InvokeScript("ShowMessage", o);
        }
        private void frmMain_Load(object sender, EventArgs e)
        {
            this.webBrowser1.Navigate(@"E:\Projects\2010\WebBrowserJavaScriptExample\WebBrowserJavaScriptExample\TestPage.htm");
        }
        [ComVisible(true)]
        public class ScriptManager
        {
            frmMain _form;
            public ScriptManager(frmMain form)
            {
                _form = form;
            }
            public void ShowMessage(object obj)
            {
                MessageBox.Show(obj.ToString());
            }
        }
    }

补充：web前端 , JavaScript ,