Can't get POST data using NodeJS/ExpressJS and Postman

Add the encoding of the request. Here is an example

..
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
..

Then select x-www-form-urlencoded in Postman or set Content-Type to application/json and select raw

Edit for use of raw

Raw

{
  "foo": "bar"
}

Headers

Content-Type: application/json

EDIT #2 Answering questions from chat:

1. why it can't work with form-data?

You sure can, just look at this answer How to handle FormData from express 4

2. What is the difference between using x-www-form-urlencoded and raw

differences in application/json and application/x-www-form-urlencoded

let express = require('express');
let app = express();

// For POST-Support
let bodyParser = require('body-parser');
let multer = require('multer');
let upload = multer();

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

app.post('/api/sayHello', upload.array(), (request, response) => {
    let a = request.body.a;
    let b = request.body.b;


    let c = parseInt(a) + parseInt(b);
    response.send('Result : '+c);
    console.log('Result : '+c);
});

app.listen(3000);

Sample JSON and result of the JSON:

Set Content-typeL application/JSON: