server.js

// content of index.js
const http = require('http')
const debug = require('debug')('node-angular');
const app = require('./app');

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

  if(isNaN(port)){
    return val;
  }

  if(port >= 0){
    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);