how to run server via expressjs code example

Example: create server with express js

// npm init
// npm i express

const express = require('express');
const server = express();

const PORT = 3000;

// Body parser
server.use(express.json());

// Homme page
server.get('/', (req, res) => {
  return res.send("<h1 style='text-align: center;'>Hello,<br />from the Express.js server!</h1>");
})

// About page
server.get('/about', (req, res) => {
  return res.send('<h2 style="text-align:center">About us</h2>');
})

// 404 page
server.use((req, res, next) =>{
  res.status(404);

  // respond with html page
  if (req.accepts('html')) {
    res.sendFile(__dirname + '/error404.html');
    return;
  }
  // respond with json
  else if (req.accepts('json')){
    res.send({
      status: 404,
      error: 'Not found'
    });
    return;
  }
  // respond with text
  else {
    res.type('txt').send('Error 404 - Not found');
  }
});

// Listening to the port
server.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});