server.js

const { debug } = require('console')
const http = require('http')
const app = require('./backend/app')

const normalizePort = val => {
    var port = parseInt(val, 10)

    if (isNaN(port)) {
        //named pipe
        return val
    }

    if (port >= 0) {
        //port number
        return port
    }

    return false
}

const onError = error => {
    if (error.syscall !== "listen") {
        throw error
    }
    const bind = typeof addr === "string" ? "pipe" + addr : "port " + port

    switch (error.code) {
        case "EACCES":
            console.error(bind + " requires elevated privileges")
            process.exit(1)
            break
        case "EADDRINUSE":
            console.error(bind + " is already in use")
            process.exit(1)
            break
        default:
            throw error
    }
}

const onListening = () => {
    const addr = server.address()
    const bind = typeof addr === "string" ? "pipe" + addr : "port " + port
    debug("Listening on " + bind)
}

const port = normalizePort(process.env.PORT || "3000")
app.set("port", port)

const server = http.createServer(app)
server.on("error", onError)
server.on("listening", onListening)
server.listen(port)