Server node express : request.body est toujours vide

'use strict'

const express = require('express')
const bodyParser = require('body-parser')
const fs = require('fs')

const app = express()

// parse application/json
app.use(bodyParser.json())

// parse application/x-www-form-urlencoded
app.use(bodyParser.urlencoded({ extended: true }))

const PORT = 8080
const HTTP_OK = 200
const CONTENT_TYPE_JSON = 'application/json'
const CONTENT_TYPE_HTML = 'text/html'

app.post('/add', function (request, response) {
    response.setHeader('Access-Control-Allow-Origin', '*')
    response.setHeader('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept')
    response.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS, HEAD')

    const body = JSON.stringify(request.body)
    fs.writeFileSync('resultdata.js', body, {})
    response.writeHead(HTTP_OK, { 'Content-Type': CONTENT_TYPE_JSON })
    response.end(body)
})

app.listen(PORT, function (){
    console.log('Server listening on: http://localhost:%s', PORT)
})