极其简单，自行扩展

HTML代码

#lt;%@ Page Language=”C#” AutoEventWireup=”true” CodeFile=”Default.aspx.cs” Inherits=”_Default” %#gt;

#lt;!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN” “http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd“#gt;
#lt;html xmlns=”http://www.w3.org/1999/xhtml“#gt;
#lt;head runat=”server”#gt;
#lt;title#gt;Untitled Page#lt;/title#gt;
#lt;script type=”text/javascript”#gt;
function GetUser()
{
requestSimpleService = WebServiceSample.GetUser(document.getElementById(’UserName’).value, OnRequestComplete);
return false;
}
//显示提示信息
function OnRequestComplete(result)
{
if(result == ‘true’)
{
document.getElementById(’Message’).innerHTML = ‘提示:用户名已被注册.’;
document.getElementById(’PostButton’).disabled = ‘disabled’;
}
else
{
document.getElementById(’Message’).innerHTML = ‘提示:用户名可以使用.’;
document.getElementById(’PostButton’).disabled = ”;
}
}
#lt;/script#gt;
#lt;/head#gt;
#lt;body#gt;
#lt;form id=”form1″ runat=”server”#gt;
#lt;asp:ScriptManager ID=”ScriptManager1″ runat=”server”#gt;
#lt;Services#gt;
#lt;asp:ServiceReference Path=”WebServiceSample.asmx” /#gt;
#lt;/Services#gt;
#lt;/asp:ScriptManager#gt;
#lt;input id=”UserName” type=”text” onblur=”return GetUser()” /#gt;
#lt;input id=”PostButton” type=”button” value=”注 册” disabled=”disabled” /#gt;#lt;br /#gt;
#lt;div id=”Message”#gt;#lt;/div#gt;
#lt;/form#gt;
#lt;/body#gt;
#lt;/html#gt;

WebService代码

using System;
using System.Web;
using System.Collections;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Web.Script.Services;

/// #lt;summary#gt;
/// WebServiceSample 的摘要说明
/// #lt;/summary#gt;
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[ScriptService]

public class WebServiceSample : System.Web.Services.WebService
{

public WebServiceSample () {

//如果使用设计的组件，请取消注释以下行
//InitializeComponent();
}

[WebMethod]
public string GetUser(string strUser)
{
string strMessage = null;
if (strUser == “ADMIN”)
{
strMessage = “true”;
}
else
{
strMessage = “false”;
}
return strMessage;
}
}