serveur.js

// Installer fs-promise avec : npm install fs-promise

const http = require('http')
const fs = require('fs-promise')

function factorial (n) {
  return n === 0 ? 1 : n * factorial(n - 1)
}

const server = http.createServer((req, res) => {
  if (req.url === '/') {
    serveFile(res, 'index.html', 'text/html')
  } else if (req.url === '/client.js') {
    serveFile(res, 'client.js', 'application/javascript')
  } else if (req.url.match(/^\/factorial\//)) {
    const number = parseInt(req.url.replace(/^\/factorial\//, ''))
    handleNumber(res, number)
  } else {
    res.statusCode = 404
    res.end('Page introuvable')
  }
})

function serveFile (res, path, contentType) {
  fs.readFile(path, 'utf-8')
    .then(content => {
      res.setHeader('Content-type', contentType)
      res.end(content)
    })
    .catch(err => {
      console.error(err.stack)
      res.statusCode = 500
      res.end('Une erreur s\'est produite')
    })
}

function handleNumber (res, number) {
  if (isNaN(number)) {
    res.statusCode = 400
    res.end('Nombre invalide')
  } else if (number < 0) {
    res.statusCode = 400
    res.end('Le nombre doit être positif')
  } else {
    res.end(String(factorial(number)))
  }
}

server.listen(3000, () => {
  console.log('Listening on http://localhost:3000/')
})