Using environment variable on NodeJS app

app.js

const http = require('http');

const PORT = 8080;

const server = http.createServer((req, res) => {
  const MYSQL_CONNECTION = process.env.MYSQL_CONNECTION;
  const MYSQL_USER = process.env.MYSQL_USER;
  const MYSQL_PASSWORD = process.env.MYSQL_PASSWORD;
});

server.listen(PORT, (err) => {
  if (err) {
    console.error('Something went wrong', err);
    process.exit(1);
  }
  
  console.log(`Server is listening to port ${PORT}`);
});