Advanced Functions Tutorial

Advanced Functions

Learn callbacks, closures, higher-order functions, and function patterns.

Functions are one of the most important building blocks in JavaScript. Once you understand basic functions, advanced function concepts make your code more powerful, reusable, and efficient.

Why Learn Advanced Functions?

Reuse code more effectively
Create flexible programs
Handle asynchronous operations
Organize complex logic
Build scalable applications

Callback Functions

javascript

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

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

greet("John", sayBye);

Output:

javascript

Hello John
Goodbye!

Higher-Order Functions

javascript

function performOperation(operation, a, b) {
    return operation(a, b);
}

function add(x, y) {
    return x + y;
}

console.log(performOperation(add, 5, 3));

Output:

javascript

Methods like map(), filter(), and reduce() are higher-order functions.

Closures

javascript

function counter() {
    let count = 0;

    return function() {
        count++;
        return count;
    };
}

const increment = counter();

console.log(increment());
console.log(increment());

Output:

javascript

1
2

Closures are useful for maintaining private data and reusable functionality.

Recursion

javascript

function countdown(number) {
    if (number === 0) {
        return;
    }

    console.log(number);

    countdown(number - 1);
}

countdown(5);

Output:

javascript

Immediately Invoked Function Expression

javascript

(function() {
    console.log("I run immediately!");
})();

Output:

javascript

I run immediately!

Real-World Example

javascript

function calculatePrice(price, discountFunction) {
    return discountFunction(price);
}

function applyDiscount(price) {
    return price * 0.9;
}

console.log(calculatePrice(1000, applyDiscount));

Output:

javascript

Summary

Advanced functions extend the power of JavaScript. Callback functions, higher-order functions, closures, recursion, and IIFEs are widely used in modern applications and prepare you for frameworks and real-world projects.