Example of having server in separate file express.js

server.js

//ES6(ES2015) used
const express = require('express')
const http = require('http')
const app = require('./server/app')

const port = process.env.PORT || 8080
const server = http.createServer(app)

server.listen(port, () => {
  console.log(`App started. Listening on port:${port}`)
})

/*
http.createServer(app).listen(port, () => {
  console.log(`App started. Listening on port:${port}`)
})
*/