Jquery ajax执行顺序 返回自定义错误信息

   由于Jquery中的Ajax的async默认是true(异步请求),如果想一个Ajax执行完后再执行另一个Ajax, 需要把async=false就可以了.

代码 function TestAjax(){
            var UserName = $("#txtUserName").val();
            $.ajax(
            {
                url: "AjaxCheckUserName.htm",
                async: false,
                success: function (data) {
                    alert(data);
                }
            });
            alert('Test');
            $.ajax({
                url: "AjaxHandler.ashx",
                async: false,
                data: "UserName=" + UserName,
                success: function (data) {
                    $("#divAjax").html(data);
                },
                error: function (msg) {
                    alert(msg.responseText);
                }
            });
        }

2. 返回自定义错误

设置 StatusCode = 500,

触发Ajax的错误(error), 在接收到数据显示自定义信息

error: function (msg) {
                    alert(msg.responseText);
                } 

 context.Response.StatusCode = 500;
 context.Response.Write("请输入用户名");

代码 string sUserName = context.Request.QueryString["UserName"];
            if (!string.IsNullOrEmpty(sUserName))
            {
                context.Response.Write(string.Format("Hello {0}!", sUserName));
            }
            else
            {
                context.Response.StatusCode = 500;
                context.Response.Write("请输入用户名");
            }

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