express

                                    const express = require('express')
const cors = require('cors')
const bodyParser = require('body-parser')
require('dotenv').config()
const ObjectId = require("mongodb").ObjectId;

const app = express()
app.use(cors())
app.use(express.json())
const port = process.env.PORT || 5000;

app.get('/', (req, res)=>{
    res.send('welcome to backend')
})

app.listen(port, () => {
    console.log(`App listening at localhost:${port}`);
})

                                    npm install express
npm install express --save
Docs : https://expressjs.com/
- Example API : https://jareer.xyz/ - 

                                    Express.js, or simply Express, is a web application framework for Node.js,
released as free and open-source software under the MIT License.

It is designed for building web applications and APIs.
It has been called the de facto standard server framework for Node.js.

                                    # You can run the application generator with the npx command (available in Node.js 8.2.0).
npx express-generator
# For earlier Node versions, install the application generator as a global npm package and then launch it:
npm install -g express-generator
# For example, the following creates an Express app named myapp. The app will be created in a folder named myapp in the current working directory and the view engine will be set to Pug:
express --view=pug myapp

   create : myapp
   create : myapp/package.json
   create : myapp/app.js
   create : myapp/public
   create : myapp/public/javascripts
   create : myapp/public/images
   create : myapp/routes
   create : myapp/routes/index.js
   create : myapp/routes/users.js
   create : myapp/public/stylesheets
   create : myapp/public/stylesheets/style.css
   create : myapp/views
   create : myapp/views/index.pug
   create : myapp/views/layout.pug
   create : myapp/views/error.pug
   create : myapp/bin
   create : myapp/bin/www
# Then install dependencies:
cd myapp
npm install
# On MacOS or Linux, run the app with this command:
DEBUG=myapp:* npm start
# On Windows Command Prompt, use this command:
set DEBUG=myapp:* & npm start
# On Windows PowerShell, use this command:
$env:DEBUG='myapp:*'; npm start

                                    const http = require('http');
const app = require('./app');

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

  if (isNaN(port)) {
    return val;
  }
  if (port >= 0) {
    return port;
  }
  return false;
};
const port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

const errorHandler = error => {
  if (error.syscall !== 'listen') {
    throw error;
  }
  const address = server.address();
  const bind = typeof address === 'string' ? 'pipe ' + address : '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 server = http.createServer(app);

server.on('error', errorHandler);
server.on('listening', () => {
  const address = server.address();
  const bind = typeof address === 'string' ? 'pipe ' + address : 'port ' + port;
  console.log('Listening on ' + bind);
});

server.listen(port);