main.js

#!/usr/bin/env node

/**
 * Module dependencies.
 */
let app = require("./app")
let debug = require("debug")("server")
let http = require('http')

/**
 * Get port from environment and store in Express.
 */
let port = normalizePort(process.env.PORT || '3000')
app.set('port', port)

/**
 * Create HTTP server.
 */
let main = http.createServer(app)
main.on('error', onError)
main.on('listening', onListening)

/**
 * Listen on provided port, on all network interfaces.
 */
main.listen(port)

/**
 * Normalize a port into a number, string, or false.
 */
function normalizePort(val) {
    let port = parseInt(val, 10)
    if (isNaN(port)) {
        return val
    }
    if (port >= 0) {
        return port
    }
    return false
}

/**
 * Event listener for HTTP server "error" event.
 */
function onError(error) {
    if (error.syscall !== 'listen') {
        throw error
    }

    let bind = typeof port === 'string'
        ? 'Pipe ' + port
        : 'Port ' + port

    // handle specific listen errors with friendly messages
    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
    }
}

/**
 * Event listener for HTTP server "listening" event.
 */
function onListening() {
    let addr = main.address()
    let bind = typeof addr === 'string'
        ? 'pipe ' + addr
        : 'port ' + addr.port
    debug('Listening on ' + bind)
}