完整的ajax

error:
服务器连接不上，或是返回内容有错误，就走这里
通常可以使用这玩意排错
beforeSend:
ajax一执行，就立马执行这个方法

complete:
ajax里的success或是error执行完毕，立马执行这里

跳转界面：window.location.href="";

三级联动小练习：

html页

<select id="sel1">
        <option>加载中...</option>
    </select>省
    <select id="sel2">
        <option>加载中...</option>
    </select>市
    <select id="sel3">
        <option>加载中...</option>
    </select>区
    
    <script type="text/javascript">
        city($("#sel1"), "0001", '1');

        $("#sel1").change(function () {
            city($("#sel2"), $("#sel1").val(), '2');
        });

        $("#sel2").change(function () {
            city($("#sel3"), $("#sel2").val(), '3');
        });

        function city(sel, code, count) {
            $.ajax({
                url: "Ashxs/bbbb.ashx",
                data: { "code": code },
                type: "post",
                dataType: "json",
                success: function (data) {
                    sel.empty();
                    for (i in data) {
                        sel.get(0).add(new Option(data[i].name, data[i].code));
                    }
                    if (count == '1')
                    {
                        aaaa($("#sel2"), $("#sel1").val(),'2');
                    }
                    if (count == '2')
                    {
                        aaaa($("#sel3"), $("#sel2").val(), '3');
                    }
                }//success
            });//ajax
        }//封装方法

    </script>

一般处理程序

   datauserDataContext con = new datauserDataContext();

    public void ProcessRequest(HttpContext context)
    {
        string end = "[";
        int count = 0;

        string code = context.Request["code"];

        List<ChinaStates> list = con.ChinaStates.Where(r => r.ParentAreaCode == code).ToList();

        if (list.Count > 0)
        {
            foreach (ChinaStates c in list)
            {
                if (count <= 0)
                {
                    end += "{"name":"" + c.AreaName + "","code":"" + c.AreaCode + ""}";
                }
                else
                {
                    end += ",{"name":"" + c.AreaName + "","code":"" + c.AreaCode + ""}";
                }
                count++;
            }
        }

        end += "]";
        context.Response.Write(end);
    }