📦 Day 4: Node.js Core Modules – path, os, and events

👨‍🏫 What You’ll Learn Today:

• What are core modules in Node.js?

• How to use the path module

• How the os module helps with system info

• How to work with events using the events module

• Real-life practical examples

• FAQs to clear your doubts

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🔹 What Are Core Modules?

Core modules are built-in tools provided by Node.js.
You don't need to install them separately — just use require() to include them in your file.

Today we’ll learn 3 important ones:

• path – To work with file and folder paths

• os – To get system-related information

• events – To create and handle custom events

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📁 1. path Module – Handling File Paths

The path module is used to build and work with file and folder paths across different operating systems (Windows, Linux, macOS).

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📌 Example 1: Joining Paths

const path = require('path');

const fullPath = path.join(__dirname, 'files', 'info.txt');
console.log('Full Path:', fullPath);

✅ path.join() safely combines folders/files into one full path.

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📌 Example 2: Get File Name and Extension

const filePath = '/home/user/app.js';

console.log('File Name:', path.basename(filePath));     // app.js
console.log('Extension:', path.extname(filePath));       // .js

📌 Useful for:

• Logging file uploads

• File processing

• Organizing folder structures

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💻 2. os Module – System Info from Node.js

The os module gives you information about the operating system you are working on.

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📌 Example: Basic OS Info

const os = require('os');

console.log('OS Type:', os.type());             // e.g. Windows_NT
console.log('Platform:', os.platform());        // e.g. win32
console.log('Free Memory:', os.freemem());      // in bytes
console.log('Home Directory:', os.homedir());

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📌 Example: System Uptime

console.log('System Uptime (seconds):', os.uptime());

✅ Useful in:

• Monitoring apps

• Logging server behavior

• Displaying server dashboard info

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🔔 3. events Module – Handling Custom Events

The events module allows you to create your own events and respond to them — just like clicking a button in the browser triggers an event.

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📌 Step-by-Step Example:

const EventEmitter = require('events');  // Import
const emitter = new EventEmitter();      // Create instance

// Listener
emitter.on('userRegistered', (name) => {
  console.log(`Welcome, ${name}! Your account is ready.`);
});

// Trigger (emit) the event
emitter.emit('userRegistered', 'Payal');

✅ Output:

Welcome, Payal! Your account is ready.

🧠 This is how backend apps handle:

• Login success events

• New order placed events

• Email sent notifications

• Custom logs

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💼 Real-Life Use Case (Mini Project Example)

Let’s create a simple event system for file download log:

const fs = require('fs');
const EventEmitter = require('events');
const emitter = new EventEmitter();

// Event listener
emitter.on('fileDownloaded', (fileName) => {
  fs.appendFileSync('download-log.txt', `Downloaded: ${fileName}\n`);
  console.log(`${fileName} logged successfully.`);
});

// Simulate file download
emitter.emit('fileDownloaded', 'resume.pdf');

✅ This logs every file download into download-log.txt.

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❓ FAQs – Common Doubts

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1) Why do we use path.join() instead of string concatenation like __dirname + '/folder/file.txt'?

✅ path.join() is cross-platform and automatically adds the correct separator (/ or \) depending on OS.
Manual concatenation may break your code on other systems.

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2) What’s the difference between os.type() and os.platform()?

Use both for debugging or logging system environments.

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3) Can we create multiple custom events using the events module?

✅ Yes! You can create as many custom events as needed.
Each one should have a listener (.on) and emitter (.emit).

emitter.on('login', () => console.log('User logged in'));
emitter.emit('login');

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4) Do I need to install path, os, or events?

❌ No need to install — these are core modules in Node.js.
Just import using require() like:

const path = require('path');

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📝 Practice Tasks for You

1. Use path to get the name and extension of a file.

2. Use os to log current system memory and platform.

3. Create a custom event called userDeleted and print a goodbye message.

4. Log system uptime using os.uptime().

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✅ Summary

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You're now ready to use system-level power tools in Node.js! 🎯

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