为什么用$.ajax()的时候，success方法没有执行，我在firefox里设了断点，它直接跳过了

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="flot.aspx.cs" Inherits="flot" %>



<%@ Register Assembly="DevExpress.Web.v12.2, Version=12.2.10.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a"

    Namespace="DevExpress.Web.ASPxEditors" TagPrefix="dx" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

    <link href="Styles/layout.css" rel="stylesheet" type="text/css" />

    <script src="Scripts/jquery.js" type="text/javascript"></script>

    <script src="Scripts/jquery.flot.js" type="text/javascript"></script>

    <script src="Scripts/jquery.flot.stack.js" type="text/javascript"></script>

    <!--[if lte IE 8]><script language="javascript" type="text/javascript" src="Scripts/excanvas.min.js"></script><![endif]-->

    <title></title>

</head>

<body>

    <form runat="server">

    <h1>

        学生成绩</h1>

    <div id="placeholder" style="width: 600px; height: 300px;">

    </div>

    <div>

        <dx:ASPxButton ID="btnShow" runat="server" Text="显示" AutoPostBack="False">

        </dx:ASPxButton>

    </div>

    <script id="source" type="text/javascript">

        $(document).ready(function () {

            $('#btnShow').click(function () {

                var dat = [];

                var data;

                $.ajax({

                    type: "POST",

                    url: "flot.aspx/heh",

                    data: "{}",

                    dataType: "JSON",

                    //cache: false,

                    //async:false,

                    contentType: "application/json; charset=utf-8",

                    success: function (data) {

                        if (data != null) {

                            //var dataObj = eval("[" + data + "]");

                            var back = $.parseJSON(data);

                            for (var i = 0; i < back.data.length - 1; i++) {

                                dat.push([back.data[i], back.data[i + 1]]);

                                i++;

                            }

                        }

                    },

                    error: function (XMLHttpRequest, textStatus, errorThrown) {



                        alert(errorThrown);

                    }

                });



                var stack = 0, bars = true, lines = false, steps = false;

                function plotWithOptions() {

                    $.plot($("#placeholder"), [dat], {

                        series: {

                            stack: stack,

                            bars: { show: bars, barWidth: 0.6 }

                        }

                    });

                }

                plotWithOptions();

            });

        });  

    </script>

    </form>

</body>

</html>

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Data;

using System.Web.Script.Serialization;

using System.Collections;

using System.Text;

using Newtonsoft.Json;

using DevExpress.Utils.OAuth.Provider;



public partial class flot : System.Web.UI.Page

{

    protected void Page_Load(object sender, EventArgs e)

    {

        

    }

    [System.Web.Services.WebMethod()]

    public static string heh()

    {

        JavaScriptSerializer jss = new JavaScriptSerializer();

        //int[,] data = new int[4, 2];

        JSON js = new JSON();

        js.data = new int[4, 2];

        js.data[0, 0] = 1; js.data[0, 1] = 24; js.data[1, 0] = 2; js.data[1, 1] = 35; js.data[2, 0] = 3; js.data[2, 1] = 19; js.data[3, 0] = 4; js.data[3, 1] = 30;

        //Response.Write(jss.Serialize(data));

        js.label = "fhjksjk";

        return jss.Serialize(js);

    }

    public class JSON

    {

        public int[,] data;

        public string label;



    }

}