1. Create Custom / Local Modules and Export Them Using Various Module Patterns

a. CommonJS Pattern (module.exports)

mathUtils.js:

function add(a, b) {
  return a + b;
}
function subtract(a, b) {
  return a - b;
}
module.exports = { add, subtract };

app.js:
const math = require('./mathUtils');
console.log(math.add(5, 3));        // 8
console.log(math.subtract(9, 4));   // 5

b. Exports Shortcut Pattern
greet.js:
exports.sayHello = (name) => `Hello, ${name}!`;
exports.sayBye = (name) => `Bye, ${name}!`;

app.js:
const greet = require('./greet');
console.log(greet.sayHello('Sam'));  // Hello, Sam!

c. Immediately Invoked Function Expression (IIFE)
counter.js:
module.exports = (function () {
  let count = 0;
  return {
    increment: () => ++count,
    decrement: () => --count,
  };
})();

app.js:
const counter = require('./counter');
console.log(counter.increment());  // 1
console.log(counter.increment());  // 2

2. Explore the Functionality of os, path, util, and events Modules

os Module:
const os = require('os');
console.log(os.platform());
console.log(os.cpus());
console.log(os.freemem());

path Module:
const path = require('path');
console.log(path.basename(__filename));
console.log(path.join(__dirname, 'files', 'test.txt'));

util Module :
const util = require('util');
const wait = util.promisify(setTimeout);
wait(1000).then(() => console.log('1 second passed'));

events Module :
const EventEmitter = require('events');
const emitter = new EventEmitter();
emitter.on('greet', (name) => {
  console.log(`Hello, ${name}`);
});
emitter.emit('greet', 'Alice');

3. Use the fs Module for Creating Directories and Files of Different Formats

const fs = require('fs');
const path = require('path');
// Create directory
fs.mkdirSync(path.join(__dirname, 'output'), { recursive: true });
// Create text file
fs.writeFileSync(path.join(__dirname, 'output', 'note.txt'), 'This is a text file.');
// Create JSON file
const data = { name: 'Node', type: 'runtime' };
fs.writeFileSync(path.join(__dirname, 'output', 'data.json'), JSON.stringify(data, null, 2));

4. Read and Write Streaming Data Using Readable and Writable Streams

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

// Create read and write streams
const readStream = fs.createReadStream(path.join(__dirname, 'input.txt'), 'utf-8');
const writeStream = fs.createWriteStream(path.join(__dirname, 'output', 'output.txt'));
// Pipe data from input.txt to output.txt
readStream.pipe(writeStream);

Make sure to create an input.txt file before running this.