Why is the XMLHttpRequest request body returning null?

I am trying to send a ‘POST’ XMLHttpRequest to my server, which uses express.
The server is able to recieve the request, but the request’s body is null.

On the server I am receiving it with :

app.post('/', function(req, res){
    res.send(req.statusCode);
    console.log(req.body);
})

I don’t think that there is a problem with it as many sources say that this is a good way to receive the request.

This is my client side code :

const user = {
    'Key' : 'user',
    'Name' : 'user',
    'Email' : 'user@example.com',
    'Password' : 'password'
}

const jsonFileRequest = new XMLHttpRequest();
jsonFileRequest.open('POST', '/', true);
jsonFileRequest.setRequestHeader('Content-Type', 'application/json');

jsonFileRequest.onreadystatechange =  function(){
    console.log(`userStatus : ${jsonFileRequest.readyState},\nstatus: ${jsonFileRequest.status}`);
    if(jsonFileRequest.readyState == 4 && jsonFileRequest.status == 200)
    {
        console.log(`userStatus : ✅,\nstatus : ✅`);

    }
}
jsonFileRequest.send(JSON.stringify(user));

**This is my server side code : **

const express = require('express');
const app = express();
const port = 8080;

app.get('/', (req, res) => {
    res.sendFile(__dirname + '/frontend/index.html');
    app.get('/index.html.js', (req, res) => {
        res.sendFile(__dirname + '/frontend/index.html.js');
    })
    app.get('/data.json', (req, res) => {
        res.sendFile(__dirname + '/data.json');
    })
})
app.post('/', function(req, res){
    res.send(req.statusCode);
    console.log(req.body);
})
app.listen(port);
console.log(`listening on http://localhost:${port}`);

Could you please help me? Thank you!

>Solution :

You should try using the express.json() middleware. When disabled (by default), req.body returns undefined.

You can check out the express documentation for more info:

req.body

Contains key-value pairs of data submitted in the request
body. By default, it is undefined, and is populated when you use
body-parsing middleware such as express.json() or
express.urlencoded().

See: https://expressjs.com/en/api.html

Using the following code snippet for your express server should work:

// Importing the express module
var express = require('express');

// Initializing the express and port number
var app = express();
var PORT = 3000;

// Calling the express.json() method for parsing
app.use(express.json());

// Reading content-type
app.post('/', function (req, res) {
   console.log(req.body.name)
   res.end();
})

// Listening to the port
app.listen(PORT, function(err){
   if (err) console.log(err);
   console.log("Server listening on PORT", PORT);
});