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Fetch API not posting to Node.js server (body is empty)

I'm trying to use fetch() to post to another Node.js server I am running. When I take out the headers, my console prints '{}'. When I keep them in, nothing is printed when I call the function.
I have tried using curl and I receive '{}' as well.
//Server.js (what I am trying to POST to)
var express = require('express');
var app = express();
var PORT = 4000;
app.use(express.json());
app.post('/', function (req, res) {
console.log(req.body);
})
app.listen(PORT, function () {
console.log('server running on port: ' + PORT);
})
//Post function (this is inside a separate React component which will perform the POST)
postContents() {
var data = { username: 'example' };
fetch('http://localhost:4000/', {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
body: JSON.stringify(data)
})
.then(response => response.json())
.catch(error => console.error('Error:', error))
.then(response => console.log('Success:', JSON.stringify(response)));
}

You have to use the body-parser as a middleware for your express server.
const express = require('express');
const app = express();
const PORT = 4000;
const bodyParser = require('body-parser');
app.use(bodyParser.json());

without headers and with headers the result is different
the URL is fully qualified with host and port
These two points suggest you are making a cross origin request.
The solution is to have the server
accept and handle OPTIONS requests when required
issue CORS headers in the response

The body of my Angular post request is empty

So the body of my Angular post request is empty on my server. The post request from my client application is:
var data = {
Stime: '+this.Stime+',
Etime: '+this.Etime+',
eAMPM: '+this.eAMPM+',
sAMPM: '+this.sAMPM+',
id: '+this.id+',
activity: '+this.activity+',
auto_insert: '+this.auto_insert+',
yearmonthday: '+this.yearmonthday+',
color1: '+this.c+'
}
this.$http({
method: 'POST',
url: 'http://localhost:3000/operation',
data: JSON.stringify(data)
})
before I tried using this post request I just had a very long query string and this passed the data just fine. But I am cleaning up my code now and this way isnt working.
On my server I have:
app.post('/operation', function(req,res){
console.log(req.body); //prints {}
res.send("inserted");
});
Also on the server side I have
var express = require('express'),
app = express(),
bodyParser = require('body-parser'),
cookieParser = require('cookie-parser'),
multer = require('multer'),
jsonParser = bodyParser.json()
app.use(jsonParser)
app.use(bodyParser.urlencoded({
extended: true
}))
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));

Inside app.post(...) {} you need to wait for data to become available like this:
var body = '';
req.on('data',function(data) { body += data; });
req.on('end', function(data) {
req.body = JSON.parse(body);
conosle.log(request.body);
});

Node.js send data to backend with AJAX

I'm quite new to AJAX, so sorry for potential missunderstandings, but I'm not completely through that thing.
I'm trying a simple thing. I have a server.js file, which is my backend basically. Then I have a index.html and a script.js. That's all, so a very basic setup. Now, on my script.js, I'm getting some data (a mail address). Now I want to send that data to my backend (into the server.js) to work with it there. How can I do this?
I found some posts already about AJAX with node.js, but I don't get it, especially not where to receive it in my backend. I'm using express for the server by the way.
What I have in my script.js is:
$.ajax({
type: "POST",
url: "server.js",
data: { mail: mail },
success: function(data) {
},
error: function(jqXHR, textStatus, err) {
alert('text status '+textStatus+', err '+err)
}
});
Right so far? How can I now receive the information in my server.js?
There's not much in so far, just:
var express = require('express');
var app = express();
var server = app.listen(3000);
app.use(express.static('public'));
Thanks for any help :)

Note: This was written before the question was updated with the code so the field names and port numbers that I used here as examples may need to be updated with the correct values.
Client-side code - example with jQuery:
$.post('/email', { address: 'xxx#example.com' });
(this can take optional callbacks and it returns a promise that can be used to add a success/error handler)
Server-side code - example with Express:
const express = require('express');
const bodyParser = require('body-parser');
const dir = path.join(__dirname, 'public');
const app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.post('/email', (req, res) => {
// you have address available in req.body:
console.log(req.body.address);
// always send a response:
res.json({ ok: true });
});
app.use(express.static(dir));
app.listen(4443, () => console.log('Listening on http://localhost:4443/'));
This assumes that your static files (HTML, client-side JavaScript, CSS) are in the public directory relative to your server.js file.
See this for background on the JSON/form-encoding issue:
Which method is prefer when building API
See this for background on serving static files:
How to serve an image using nodejs

That's actually quite simple to implement in Express.JS with the basic router:
I'm gonna give you the minified code snippets to help you get sense of how it works across browser and server.
in Front-End, you basically just want to "post" an email address to the backend:
$.post('/email', { email: 'howareyou#xx.com' })
and in Back-End(Express.JS), you should implement the basic router:
var express = require('express');
var app = express();
// use: app.METHOD(PATH, HANDLER)
app.post('/email/', function(req, res) {
var email = req.body.email
})
Read more here: http://expressjs.com/en/guide/routing.html

First, you need a valid route to hit when the server is running. You can do this in server.js through express.
var express = require('express');
var bodyParser = require('body-parser');
var app = express();
app.use(bodyParser.json());
app.use(express.static('public'));
app.post('/mail', function(req, res) {
var body = req.body;
console.log('email', body.email);
res.json({ message: 'I got the email!' });
});
var server = app.listen(3000);
Notice I have brought in an express middleware that will parse the body for JSON and make it available on the req object under req.body. You will need to install this dependency with npm install --save body-parser.
Then you need to send a POST request to that URL from the front-end.
$.ajax({
type: "POST",
url: "/mail",
data: { mail: mail },
success: function(data) {
console.log('message', data.message);
},
error: function(jqXHR, textStatus, err) {
alert('text status '+textStatus+', err '+err)
}
});
Now, if you submit an email, you should see a log in your terminal that shows the email and a log in your developer console in the browser that shows the message "I got the email!"

in server.js add this :
app.post('/searching', function(req, res){
//do something with req
});
and in script.js :
$.ajax({
type: "POST",
url: "/searching",
data: { mail: mail },
success: function(data) {
},
error: function(jqXHR, textStatus, err) {
alert('text status '+textStatus+', err '+err)
}
});

First of all you nedd to create a route for the Mail
var express = require('express');
var path = require('path');
var bodyParser = require('body-parser');
var app = express();
var router=app.Router();
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false })); // Parse request body
app.use(express.static(path.join(__dirname, 'public')));
// Route to check Email
router.post('/CheckEmail',(req,res)=>{
var email=req.body.mail; // Get email here
})
app.listen(process.env.port || 3000,()=>{
console.log('server is running');
})
Ajax
$.ajax({
type: "POST",
url: "/CheckEmail", // post route name here
data: { mail: mail },
success: function(data) {
},
error: function(jqXHR, textStatus, err) {
alert('text status '+textStatus+', err '+err)
}
});

You need a few more things to actually be able to parse the body. Add this to your server.js file.
var bodyParser = require('body-parser');
var cookieParser = require('cookie-parser');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
You need to specify a valid URL. Since you are listening on 3000. You also need to specify a route on your server as an endpoint.
$.ajax({
type: "POST",
url: "http:localhost:3000/",
data: { mail: mail },
success: function(data) {
},
error: function(jqXHR, textStatus, err) {
alert('text status '+textStatus+', err '+err)
}
});
Now you need to add a route on your server. You can do so by adding this to your server.js file after all of the app.use calls
app.post("/", function(req, res){
// your logic here
res.send("I am sending something back!");
})

Angular JS to Node Js using Express Js

I have been trying to run a angularJs front-end with NodeJs server with expressJs. This program is merely supposed to takes user input and prints it on the server console. Having limited knowledge in JavaScript I have compiled the following codes:
Client.js
angular.module("appModule",[]).
controller("appController", function($scope,$http){
$scope.action = function () {
console.log($scope.data);
var post = $http({
method: 'POST',
url: '/Data',
data: $scope.mod,
processData: false
})
post.success(function (response) {
console.log(response);
$scope.response.data = response;
});
}
});
Server.js
var express = require('express');
var fs = require("fs");
var url = require("url")
var http = require('http');
var path = require('path');
var bodyParser = require('body-parser');
var app = express();
app.use(express.static(path.join(__dirname, 'public')));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
extended: true
}));
app.post('/Data', function (req, res) {
console.log(req.body);
res.setHeader('Content-Type', 'application/json');
req.body.serverMessage = "NodeJS replying to angular"
res.end(JSON.stringify(req.body));
});
http.createServer(function(request,response){
var pathname = url.parse(request.url).pathname;
console.log("Request for " + pathname + " received.");
fs.readFile(pathname.substr(1),function (err,data){
if(err){
console.log(err);
response.writeHead(404, {'Content-Type': 'text/html'});
}else{
response.writeHead(200, {'Content-Type': 'text/html'});
response.write(data.toString());
}
response.end();
});
}).listen(8081, function () {
console.log("Server running at http://127.0.0.1:8081/");
});
This seems to give an error on the terminal:
Server running at http://127.0.0.1:8081/
Request for /public/WebPageView.html received.
Request for /public/JavaScriptCode.js received.
Request for / received.
{ Error: ENOENT: no such file or directory, open ''
at Error (native) errno: -2, code: 'ENOENT', syscall: 'open', path: '' }
The scene of the browser was as follows
Browser Screen

#Ritik Saxena is correct. Also, you're not actually letting Express do it's job in the code you have above as you're not connecting it to the http server at all. the only code of yours actually running is the callback to the http.createServer call.
You should pass the express app to it rather than your own callback. If you want your existing callback to run you need to mount that as app middleware instead.

The last Request in your terminal output shows it receives request for /. Your code extracts / in variable pathname. In fs.readFile you provide first argument as pathname.substr(1) which boils down to null because pathname is / here. Hence, you get the corresponding error.

nodejs express 4.0 post json object

I am trying to parse the json object sent in the request and echo out the data being sent
Here is my post request
$.ajax({
url: url,
type: 'POST',
contentType: 'application/json',
data: JSON.stringify({
name:"Bob"
}),
// processData: false, // this is optional
dataType: 'json'
});
Here is how I am trying to access the object parameters
var express = require('express');
var app = express();
var bodyParser = require('body-parser');
var router = express.Router();
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use('/api', router);
app.listen(8010);
router.post('/addUser', function(req, res){
console.log(req.body);
});

I think you need :
router.post('/addUser', function(req, res){
console.log(req.body.name);
});
EDIT
After testing it, you also miss these two lines (or you didn't include them on purpose) :
app.use(router); //You need to register your rooter as a middleware
app.listen(1234); //Your port of choice

The key here is the fact that you use the middleware 'body-parser'.
What it does is simple, it parses the data and creates a body object as a parameter of your request.
Therefore, the name parameter you're looking for will be found in : req.body.name and not in param
Quote from the github page :
req.body
A new body object containing the parsed data is populated on the request object after the middleware.