create app.js in node code example

Example: node app create

using command line >>> 

npm init

open text editor create a js file. for example like index.js and paste following code.

>>> 
  
const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

----

run using 
node app.js