ASP.net Ajax 调用Web Service

HTML:

<asp:ScriptManager runat="server" ID="sm">
     <Services>
       <asp:ServiceReference Path="~/validateUserName.asmx" />
     </Services>
    </asp:ScriptManager>
    <div>
       <input type="text" id="userName"  onchange="test();"/>
       &nbsp;<span id="msg"></span>
    </div>

JS:

<script type="text/javascript">
        function test() {
            requestService = JQueryProj.validateUserName.GetUser(document.getElementById("userName").value, validate);
        }
        function validate(result) {
            
            if (result == "false") {
                msg.innerHTML = "用户名已存在!";
            }
            else {
                msg.innerHTML = "用户名可用!";
                
            }
        }
    </script>

Web Service

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Script.Services;

namespace JQueryProj
{
    /// <summary>
    /// validateUserName 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // 若要允许使用 ASP.NET AJAX 从脚本中调用此 Web 服务，请取消对下行的注释。
    [ScriptService]
    public class validateUserName : System.Web.Services.WebService
    {

        [WebMethod]
        public string GetUser(string userName)
        {
            if (userName == "admin")
            {
                return false.ToString().ToLower();
            }
            else
            {
                return true.ToString().ToLower();
                
            }
        }
    }
}