CallBack & Promises

🎯 Learning Objectives

By the end of this lecture, students will be able to:

• Understand what a callback function is
• See why callbacks are used in JavaScript
• Identify problems with callbacks (callback hell)
• Understand what a Promise is and why it exists
• Create and consume Promises
• Chain Promises to avoid callback hell
• Understand how Promises relate to the event loop (microtasks)

#️⃣ 1. What is a Callback Function?

A callback function is a function that is:

Passed as an argument to another function and executed later

🔹 Simple Example

function greet(name, callback) {
console.log("Hello " + name);
callback();
}

function sayBye() {
console.log("Goodbye!");
}

greet("Alex", sayBye);

✔ sayBye is a callback

✔ It runs after greet finishes its work