JavaScript Functions

In JavaScript, functions are reusable blocks of code designed to perform specific tasks. Think of them as small machines: you give them some input, and they return a result after processing it.

Functions allow us to avoid repeating code and to organize logic in a cleaner, more efficient way.

What Is a Function?

A function is defined once, and it can be called (used) whenever needed.

				
					function greet(name) {
  return "Hello, " + name + "!";
}

Why Use Functions?

To avoid repeating code
To organize logic into meaningful pieces
To make code easier to test, read, and reuse
To pass blocks of logic around like values (functions are first-class citizens)

Function Structure

				
					function functionName(parameters) {
  // your code goes here
  return result;
}

functionName: what you want to call it
parameters: input values (optional)
return: sends back the result

Example: A Simple Calculator

				
					function add(a, b) {
  return a + b;
}

let result = add(4, 6); // 10

You can pass any values to it—numbers, strings, even other functions!

Arrow Functions (Shorter Syntax)

Arrow functions are often used when the function is small and simple.

				
					const multiply = (x, y) => x * y;

console.log(multiply(3, 7)); // 21

If there’s just one parameter, you can skip the parentheses:

				
					const greet = name => "Hi " + name;

Function Inside Function (Nested)

You can even define functions inside other functions:

				
					function outer(num) {
  function double(x) {
    return x * 2;
  }
  return double(num) + 5;
}

console.log(outer(4)); // 13

Nested functions help in scoping and organizing logic that’s only needed inside the parent function.

Functions Are First-Class in JavaScript

In JavaScript, functions can:

Be assigned to variables
Be passed as arguments to other functions
Be returned from other functions

This makes JavaScript powerful for writing flexible and reusable code (especially in libraries and frameworks like React).

Wrap-up

Functions are a core concept in JavaScript. Whether you’re creating a calculator, form validator, or an entire app, you’ll use functions every step of the way.