init.js

const express = require('express');
const compression = require('compression');
const bodyParser = require('body-parser');
const cookieParser = require('cookie-parser');
const helmet = require('helmet');
const path = require('path');
const cors = require('cors');
const responseTime = require('response-time');
//server initialization function from ./initServer.js
const initServer = require(path.join(__dirname, 'initServer'));

module.exports.init = async function init() {
  try {
    const app = express();

    //the custom userObject, that is shared over the application via the require cache.
    require.cache.userObject = {
      app
    };

    //the base __dirname
    require.cache.userObject.appPath = __dirname;

    app.use(compression());
    app.use(bodyParser.json());
    app.use(bodyParser.urlencoded({
      extended: true,
    }));
    app.use(cookieParser());
    app.use(helmet());
    app.use(cors());
    app.use(responseTime());

    //initializing config and getting the config object
    const config = require(path.join(__dirname, '/config/index.js'));

    //initializing errorObject
    const errorObject = require(path.join(__dirname, '/config/error.js'));
    require.cache.userObject.errorObject = errorObject;

    //loading the base application router.
    const appRouter = require(path.join(__dirname, '/routes.js'));

    //initialzing the logger with the module name.
    const logger = config.logger.createLogger('init');

    // Router mounting
    app.use('/', appRouter);

    //initizing the server, with config and app.
    const { io, server } = await initServer(config, app) || {};

    //passing the socketObject to the userObject
    require.cache.userObject.io = io;

    //server object
    server.listen(config.app.server.port)
      .on('error', error => logger.error(error))
      .on('listening', () => logger.info(`Express listening on ${config.app.server.port}`));

    //catching uncaught excpetions and terminating the application.
    process.on('uncaughtException', (err) => {
      console.error('whoops! there was an error', errorObject.getError('UNCAUGHT_EXCEPTION', err));
      process.exit(0);
    });

  } catch (error) {
    console.error('Error in initializing', error);
  }
  //init express
};