jquery - Flash NodeJS 对用户出错？

Question

我使用 Ajax 和 Node JS 让用户在单页应用程序上注册。当用户点击注册时，我将其设置为检查用户名是否被占用。到目前为止，所有这些都有效。然而现在，我需要提醒用户他们的用户名已被占用。我如何以这种方式打印错误或向用户闪现错误？问题是我正在避免页面刷新。

app.post("/quiz", function(req, res, next){
    User.findOne({username: req.body.username}, function(err, user){
       if(err) { console.log(err)} 
      if(user) { 

       console.log(user)
        // I NEED TO SEND THE ERROR HERE SAYING THE USERNAME IS TAKEN     
        // I NEED TO SEND THE ERROR HERE SAYING THE USERNAME IS TAKEN     
        // I NEED TO SEND THE ERROR HERE SAYING THE USERNAME IS TAKEN     
      }

    });

       //continue with your registration logic
       var newUser = new User({username: req.body.username, datapoint: req.body.datapoint});
         User.register(newUser, req.body.password, function(err, user){


        // if(res.error){

             if(err){
               req.flash("error", err.message);
               res.redirect('back')
               return res.render("quiz");

           } else {

           passport.authenticate("local")(req, res, function(){
           //   req.flash("success", "Welcome to JobQuiz " + user.username);
             res.redirect("jobquiz");
             console.log(req.body.datapoint)
           });
           }
       });



});

Ajax 设置

   $(function() {
                $("#checkpaymentForm").on("submit", function(e) {
                    e.preventDefault();
                    $.ajax({
                    url: $(this).attr("action"),
                   type: 'POST',
                   data: $(this).serialize(),
                   dataType:'json',
                })
                });
   });

Answer 1

首先在服务器代码的 if 语句中发送您的响应:

app.post("/quiz", function(req, res, next){
    User.findOne({username: req.body.username}, function(err, user){
       if(err) { console.log(err)} 
       if(user) { 
            res.json({"message": "false" });
       }

 });

然后在前端添加成功函数来处理响应:

   $(function() {
            $("#checkpaymentForm").on("submit", function(e) {
                e.preventDefault();
                $.ajax({
                  url: $(this).attr("action"),
                  type: 'POST',
                  data: $(this).serialize(),
                  dataType: 'json',
                  success: function (data) {
                    if (data.message === "false") {
                        //TODO: alert users here
                    }
                 })
            });
   });