using System.Web.Services; 

[WebMethod]
public static string SayHello()
{return "Hello Ajax!";
}

$(function() {     $("#btn").click(function() {     $.ajax({              type: "post", //要用post方式                 url: "Demo.aspx/SayHello",//方法所在页面和方法名contentType: "application/json; charset=utf-8",     dataType: "json",     success: function(data) {                    alert(data.d);//返回的数据用data.d获取内容
            },error: function(err) {     alert(err);     }     });});
});

<form id="form1" runat="server"> <div> <asp:Button ID="btn" runat="server" Text="验证用户" /> </div> </form>

 $.ajax({  type: "POST",  url: "S_CBFBM.ashx",  data: { ZBM: p_zdm },  beforeSend: function() {  //$("#div_load").visible = "true;
           },  success: function(msg) {  //$("#div_load").visible = false;  $("#ds").html("<p>" + msg + "</p>");  $("#CBFBM").val(msg);  }  });  

    <%@ WebHandler Language="C#" Class="AjaxHandler" %>  using System;  using System.Web;  public class AjaxHandler : IHttpHandler {  public void ProcessRequest (HttpContext context) {  context.Response.ContentType = "text/plain";  if (context.Request["name"].ToString() == "admin" &&  context.Request["pass"].ToString() == "admin")  {  context.Response.Write("Y");  }  else  {  context.Response.Write("N");  }   }  public bool IsReusable {  get {  return false;  }  }  }  

  JavaScriptSerializer jsonUtil = new JavaScriptSerializer();string json = jsonUtil.Serialize(需要返回的对象);

    $.get(url,function(data){  obj= $.parseJSON(data);    //Json化之后可以用each遍历$.each(obj, function(k,v) {  alert(v.id);  });  });