Working with async functions and modules

data.txt

Some important data

module.js

module.exports = {
  add: (a, b) => a + b,
  sub: (a, b) => a - b,
  mul: (a, b) => a * b,
  div: (a, b) => a / b,
};

server.js

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

const { add } = require('./arithmetic');

const PORT = process.env.PORT || 3000;
const [_, __, a = 0, b = 0] = process.argv;

console.log(`Adding ${a} + ${b} = ${add(a, b)}`);

http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  
  fs.readFile('data.txt', (error, data) => {
    if (!error) {
      res.end(data.toString());
    } else {
      res.end('An error ocurred!', error.toString());
    }
  });
}).listen(PORT, () => {
  console.log(`Listening port ${PORT}...`);
});