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How to send JSON as respond from Node js to Html file

I'm trying to send JSON from Node js to html file as a response, but after I submit HTML form disapears and this shows up Respond after I submit a form. I tried ajax but it doesn't work beacuse I get redirected to this (image above). I'm trying to make a simple login form and if user inputs nothing then message should get displayed saying "Nothing was input" below the form.
JS code (node.js, express framework)
app.get('/login', function(req, res){
res.sendFile(path.join(__dirname+'/Frontend/html/login.html'));
});
app.post('/login', function(req, res){
res.json({a: 5});
});
html code
<form method="POST">
<input type = "text" name = "username" id = "username" placeholder="Username">
<input type = "password" name = "password" id = "password" placeholder="Password">
<button id = "gumb" type = "submit">Prijavi se</button>
</form>
<p id = "demo"></p>
<script>
document.getElementById('gumb').addEventListener('click', function(){
const xhr = new XMLHttpRequest();
console.log("test");
if(xhr.readyState == 4 && xhr.status == 200){
document.write(xhr.responseText);
}
else{
console.log("broke");
}
xhr.open('get', 'http://localhost:8000/login', true);
});
</script>

Your code works as expected, you just send a json key-value pair to your frontend, when the route is invoked. The data is shown in your browser.
app.post('/login', function(req, res){
res.json({a: 5});
});
Usually, you would want to do something with the data sent to your backend:
app.post('/login', function(req, res){
user= req.body.username;
password = req.body.password;
console.log(`User: ${user} is requesting login`);
// do something with the data - login, save, edit
res.end();
});
Since you obviously commit login data (FROM a form TO your backend),
you should use some authentification middleware to perform a login.
To comfortably send processed html to your backend, you should get acquainted with the subject of views.
And the express api documentation will be very useful to you, I'm sure. ;)
https://expressjs.com/en/api.html

formdata object is empty for html form post request

I'm trying to use formdata object to send form data to my server. I need this because one of my input fields is a file. However the formdata object is blank when I try to send the data to my server, it also prints out "{}". What is the issue? I have jquery updated to 11.1 which supports formdata. Thanks.
<form enctype="multipart/form-data" name="formName" id="formId">
<input type="text" name="name" class="form-control" id="name">
</form>
<button type="submit" class="btn btn-xl sub">Send Message</button>
<script>
$(".sub").click(function(){
var formElement = document.querySelector("form");
alert(formElement); //alert message is "[object HTMLFormElement]"
var d = new FormData(formElement);
alert(JSON.stringify(d)); //alert message is "{}"
$.post("/email",d,function(data){
alert("success!");
});
});
</script>
Server:
/*never reaches endpoint*/
app.post('/email', function(req, res) {
console.log("entered");
console.log(req.body) // form fields
console.log(req.files) // form files
var resume = req.files;
email(req.body, resume);
});
https://developer.mozilla.org/en-US/docs/Web/API/FormData/Using_FormData_Objects

How are you parsing the body of POST requests on your node server?
The issue is that FormData will set the content type to be multipart/form-data, which Express' body-parser doesn't understand.
Note the comment here:
[body-parser] does not handle multipart bodies, due to their complex and typically large nature. For multipart bodies, you may be interested in the following modules: busboy and connect-busboy; multiparty and connect-multiparty; formidable; multer.
So in other words, you have to user a different module to handle the multipart body that FormData sends. I can recommend formidable, in which case you're server code would look something like:
const formidable = require('formidable')
exports.createPost = (req, res, next) => {
var form = new formidable.IncomingForm();
form.parse(req, (err, fields, files) => {
console.log(fields)
res.send('NOT IMPLEMENTED: pollsController createPost');
}
}

Can I use body-parser and Formidable at the same time?

I am tryint to resolve a problem a couple of days, but can't understand some things.
I have a web site created with NodeJS and ExpressJS, and for handling forms I use body-parser.
var adName = req.body.adName;
var adMessage = req.body.adMessage;
var phone = req.body.phone;
var rawPrice = req.body.price;
var rawCurrency = req.body.currency;
So, using this method I handle form values.
But now, I need to use node-formidable to parse images from users. The question is, can I use somehow
formidable only for images and body-parser for forms? Or, can anyone help me with formidable, to understand how to handle forms and attach values to my variables?

You may want to take some time out to study/practice with the formidable module. See this url: https://github.com/felixge/node-formidable
Yes, formidable can be used to process both form fields and file upload including multiple file uploads. body-parser middleware does not handle multiparts - https://github.com/expressjs/body-parser. In this case, I will advise you use formidable and drop body-parser.
See if below express app help you out.
var formidable = require('formidable'),
util = require('util'),
express = require('express'),
app = express();
app.set('port', process.env.PORT || 3600);
app.get('/', function (req, res) {
res.send(
'<form action="/upload" enctype="multipart/form-data" method="post">'+
'<input type="text" name="adName" placeholder="adName"><br>'+
'<input type="text" name="adMessage" placeholder="adMessage"><br>'+
'<input type="text" name="phone" placeholder="phone"><br>'+
'<input type="text" name="rawPrice" placeholder="rawprice"><br>'+
'<input type="text" name="rawCurrency" placeholder="rawcurrency"><br>'+
'<input type="file" name="upload" multiple="multiple"><br>'+
'<input type="submit" value="Upload">'+
'</form>'
);
});
app.post('/upload', function(req, res){
var form = new formidable.IncomingForm();
form.uploadDir = __dirname + "/data";
form.parse(req, function(err, fields, files) {
//fields is an object containing all your fields, do waht ever you want with them from here
//file is an object containing properties of your uploaded file
res.send(util.inspect({fields: fields, files: files}));
console.log('file uploaded : ' + files.upload.path + '/' + files.upload.name);
console.log('Fields : ' + fields.adName);//you can access all your fields
});
});
//starting server
app.listen(app.get('port'), function () {
console.log('Express is listening: http://localhost:%s;', app.get('port'));
});

You can use both body-parser and formidable at the same time if you wish. You can use formidable just for some specific routes and continue using body-parser on the rest. Below I show the code needed to use formidable for just one route:
const formidableMiddleware = require('express-formidable');
app.post('/api/v1/uploadfile', formidableMiddleware(), async (req, res) => {
const file = req.files.file;
console.log('file info: ' + file);
const fields = req.fields;
console.log('fields = ' + JSON.stringify(fields));
});
Take a look at this link: https://github.com/utatti/express-formidable/issues/1

Passing a JSON object from clientside JavaScript to NodeJS

I have a webpage which creates a JSON object based on user input. I would like to then somehow allow the user to submit this JSON object to a NodeJS script for processing/insertion into a MySQL database. However, I'm really not sure how to do something like this -- the best I can come up with is some form of a POST, but I'm not sure where to start with this.
Because I don't know what such a method would be described as, I haven't had much success in locating any tutorials or other resources online.
Could anyone suggest some articles or documentation to look at that would be relevant to something like this? Or, at least, tell me what to search for? Thanks.
EDIT: This is the code I am trying to get working at the moment. I'm just trying to convert the POST data type from string to JSON on both sides.
Serverside:
var express = require('express');
var fs = require('fs');
var app = express();
app.use(express.bodyParser());
app.get('/', function(req, res){
console.log('GET /')
//var html = '<html><body><form method="post" action="http://localhost:3000">Name: <input type="text" name="name" /><input type="submit" value="Submit" /></form></body>';
var html = fs.readFileSync('index.html');
res.writeHead(200, {'Content-Type': 'text/html'});
res.end(html);
});
app.post('/', function(req, res){
console.log('POST /');
console.dir(req.body);
res.writeHead(200, {'Content-Type': 'text/html'});
res.end('thanks');
});
port = 8080;
app.listen(port);
console.log('Listening at http://localhost:' + port)
Clientside:
<html>
<body>
<form method="post" action="http://localhost:8080">
Name: <input type="text" name="name" />
<input type="submit" value="Submit" />
</form>
<script type="text/JavaScript">
console.log('begin');
var http = new XMLHttpRequest();
var params = "text=stuff";
http.open("POST", "http://localhost:8080", true);
http.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
//http.setRequestHeader("Content-length", params.length);
//http.setRequestHeader("Connection", "close");
http.onreadystatechange = function() {
console.log('onreadystatechange');
if (http.readyState == 4 && http.status == 200) {
alert(http.responseText);
}
else {
console.log('readyState=' + http.readyState + ', status: ' + http.status);
}
}
console.log('sending...')
http.send(params);
console.log('end');
</script>
</body>
</html>

Here is a very basic example using jQuery to do the post request and an express app. I think it should be a decent starting point.
// client side, passing data to the server
$.post("/foo/", { data : { foo : "bar" } }, function(temp) {
// temp === "I am done";
});
// serverside app.js
var express = require("express");
var app = express();
// will parse incoming JSON data and convert it into an object literal for you
app.use(express.json());
app.use(express.urlencoded());
app.post("/foo/", function(req, res) {
// each key in req.body will match the keys in the data object that you passed in
var myObject = req.body.data;
// myObject.foo === "bar"
res.send("I am done");
});
EDIT: JSON.stringify() and JSON.parse() will serialize/deserialize JSON. (jQuery makes this much easier, but if you wanna go pure javascript)
Change to var params = "text=" + JSON.stringify({ foo : "bar" });
and
console.dir(JSON.parse(req.body.text));
It worked for me on my local.

POST Request Issue in ExpressJS

I'm working with NodeJS and I'm working on letting users upload files. Right now though I'm having a lot of problem even trying to get a simple POST request.
Over in my index.ejs file I have some code that creates a form and then sends a post request:
<div id="uploaddiv">Upload things here<br>
<form action="/upload" enctype="multipart/form-data" method="post">
<input type="text" name="title"><br>
<input type="file" name="upload" multiple="multiple"><br>
<input type="submit" value="Upload">
</form>
</div>
Then in server.js, I have code that handles the uploading.
var server = express.createServer();
//bunch of stuff left out
server.get('/upload', function(req, res) {
console.log("uploading!");
if (req.method.toLowerCase() == 'post') {
res.write('lol');
}
});
My problem is that navigating directly to localhost/upload will console.log properly, but clicking on the button gives me the error "Cannot POST /upload".
Thanks!

server.get means handle an HTTP GET. You want server.post. FYI the "Cannot XXX /uri" error is what express responds with when no active route matches the request and no 404 error handler has been configured.

By using server.get(), you're instructing that route to only respond to GET requests, but the form is obviously a POST.
You should use server.post().
You can also use server.any() if you want to it respond to both GET and POST (and every other HTTP verb as well).

You should probably use Felix Geisendörfer's node-formidable to upload files.
var express = require('express'),
app = express.createServer(),
util = require('util'),
formidable = require('formidable');
app.get('/upload', function (req, res){
res.writeHead(200, {'content-type': 'text/html'});
res.end(
'<form action="/upload" enctype="multipart/form-data" method="post">'+
'<input type="text" name="title"><br>'+
'<input type="file" name="upload" multiple="multiple"><br>'+
'<input type="submit" value="Upload">'+
'</form>');
});
app.post('/upload', function (req, res) {
var form = new formidable.IncomingForm();
form.uploadDir = '.';
form.keepExtensions = true;
form.parse(req, function(err, fields, files) {
res.writeHead(200, {'content-type': 'text/plain'});
res.write('received upload:\n\n');
res.end(util.inspect({fields: fields, files: files}));
});
return;
});
app.listen(3000, '127.0.0.1');
It is just a simple as this to do file uploading thanks to node-formidable.