async config

config.js

module.exports = new Promise((resolve, reject) => {
  console.log('config module loaded!');
  const foo = {};
  getAsyncConfig(foo)
    .then(config => {
      resolve(config);
    });
});

function getAsyncConfig(foo) {
  const promise = new Promise((resolve, reject) => {
    setTimeout(() => {  
      foo.bar = function(test) {
        console.log('foo.bar() executed with ' + test);
      };

      foo.env = 'development';
      foo.port = 8080;
    
      resolve(foo);
    }, 2000);
  });

  return promise;
}

index.js

require('./config')
  .then(config => {
      console.log(config);
    require('./server')(config);
  });

server.js

const express = require('express');

function server(settings) {
  const config = {};
  Object.assign(config, settings);
  const PORT = config.port;
  const app = express();

  app.get('/', (req, res) => {
    res.send('Hello World!');
  });

  app.listen(PORT, () => {
    console.log(`server listening on port ${PORT}`);
  });

  return app;
};

module.exports = server;