1、普通ajax请求：

        para = {};
        para.action = "getUserInfo";//post请求的参数用Request.Params["action"];接收
        para.timespan = new Date().getTime();
        para.id = val;
        $.ajax({
            url: "ashx/bg_user.ashx",data: para,type: "POST",dataType: "json",success: function (data) {
                //data为json对象集合，所以此处用[0]
                return data[0].UserName;
               
            }
        });