Events vs callbacks decision in Node.js - Hands-On Comparison

Events vs Callbacks Decision in Node.js

📖 Scenario: You are building a simple Node.js program that simulates a download process. You want to learn how to handle the completion of the download using two common ways: callbacks and events.This will help you understand when to use callbacks and when to use events in Node.js.

🎯 Goal: Create a Node.js script that first uses a callback to notify when a download finishes, then refactor it to use an event emitter to notify the same.This will show you the difference between callbacks and events and when each is useful.

📋 What You'll Learn

Create a function called downloadFile that accepts a callback function

Call the callback function after simulating a download delay

Create an EventEmitter instance called downloader

Emit a done event after simulating the download delay

Listen to the done event and log a message

💡 Why This Matters

🌍 Real World

Handling asynchronous operations like file downloads, user actions, or server responses in Node.js applications.

💼 Career

Understanding callbacks and events is essential for Node.js developers to write clean, maintainable, and scalable asynchronous code.

1

Create the download function with a callback

Create a function called downloadFile that takes a callback parameter. Inside it, use setTimeout to simulate a 1 second delay, then call the callback function.

Node.js

# Create the downloadFile function with a callback
# Your code here

Need a hint?

Use setTimeout to simulate delay and call the callback inside it.

2

Call downloadFile with a callback to log completion

Call the downloadFile function and pass a callback function that logs 'Download complete using callback'.

Node.js

function downloadFile(callback) {
    setTimeout(() => {
        callback();
    }, 1000);
}

// Call downloadFile with a callback
# Your code here

Need a hint?

Pass an arrow function to downloadFile that logs the message.

3

Create an EventEmitter and emit 'done' event after delay

Import EventEmitter from 'events'. Create a constant called downloader as a new EventEmitter. Create a function called downloadFileEvent that uses setTimeout to emit a 'done' event on downloader after 1 second.

Node.js

function downloadFile(callback) {
    setTimeout(() => {
        callback();
    }, 1000);
}

downloadFile(() => {
    console.log('Download complete using callback');
});

// Import EventEmitter and create downloader
// Create downloadFileEvent function
# Your code here

Need a hint?

Use require('events') to import EventEmitter and create an instance.

4

Listen to 'done' event and call downloadFileEvent

Add a listener on downloader for the 'done' event that logs 'Download complete using event'. Then call the downloadFileEvent function.

Node.js

const EventEmitter = require('events');

function downloadFile(callback) {
    setTimeout(() => {
        callback();
    }, 1000);
}

downloadFile(() => {
    console.log('Download complete using callback');
});

const downloader = new EventEmitter();

function downloadFileEvent() {
    setTimeout(() => {
        downloader.emit('done');
    }, 1000);
}

// Listen to 'done' event and log message
// Call downloadFileEvent
# Your code here

Need a hint?

Use downloader.on('done', callback) to listen for the event.