app listen in node js

1. Import the required modules:

const express = require('express');

1. Create an instance of the Express application:

const app = express();

1. Define a route handler:

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

1. Make the application listen on a specific port:

app.listen(3000, function () {
  console.log('Example app listening on port 3000!');
});