页面JS代码如下：
方法一：
$.getJSON(
    "http://ip地址/chatService/chatService.asmx/userLogin?jsoncallback=?",
    {userId:"'"+$("#userId").val()+"'", serverId:"'"+$("#serverId").val()+"'", date:"'"+new Date()+"'"},
    function(json)
    {
       if(json.length > 0)
       {
           alert(json);                            }
       }
); 
方法二：
               $.ajax({
                    async: false，
                    type: "POST",
                    contentType:"application/json;utf-8",
                    url: "http://ip地址/chatService/chatService.asmx/userLogin?callback=?",
                    data: "{userId:'"+$("#userId").val()+"', serverId:'"+$("#serverId").val()+"', date:'"+ new Date() +"'}",
                    datatype:"json",
                    success: function(json){
                        if(json != "")
                        {
                            alert(json);
                        }
                    }
                });

web service方法
已经包含了[System.Web.Script.Services.ScriptService]

        [WebMethod]
        public void userLogin(string userId, string serverId, string date)
        {
            DBManager db = new DBManager("COM");
            SqlParameter[] p = new SqlParameter[4];
            p[0] = new SqlParameter("@userId", SqlDbType.Int, 0);
            p[0].Direction = ParameterDirection.Input;
            p[0].Value = userId;
            p[1] = new SqlParameter("@serverId", SqlDbType.Int, 0);
            p[1].Direction = ParameterDirection.Input;
            p[1].Value = serverId;
            p[2] = new SqlParameter("@date", SqlDbType.DateTime, 0);
            p[2].Direction = ParameterDirection.Input;
            p[2].Value = date;
            p[3] = new SqlParameter("@returns", SqlDbType.Int, 0);
            p[3].Direction = ParameterDirection.ReturnValue;

            int sysId = db.ExeProc("ap_webUserLog", p);
            string callback = HttpContext.Current.Request["jsoncallback"];
            string retV = "";
            retV += "({state:" + sysId + ", msg:'成功建立连接'})";
            HttpResponse response = HttpContext.Current.Response;
            response.Write(callback + retV);
            response.End();
        }