JavaScript Functions

Functions are reusable blocks of code that perform a specific task. They are one of the most important concepts in JavaScript.

Function Declaration

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

greet("Alice");   // "Hello, Alice!"
greet("Bob");     // "Hello, Bob!"

Parameters and Arguments

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

let result = add(3, 5);
console.log(result);  // 8

Return Values

function multiply(a, b) {
    return a * b;
    // Code after return is never executed
}

let product = multiply(4, 5);
console.log(product);  // 20

Function Expression

const square = function(x) {
    return x * x;
};

console.log(square(4));  // 16

Arrow Functions (Modern)

// Full arrow function
const greet = (name) => {
    return "Hello, " + name;
};

// Short form (single expression)
const double = (x) => x * 2;
const add = (a, b) => a + b;

console.log(double(5));    // 10
console.log(add(3, 4));    // 7

Default Parameters

function greet(name = "World") {
    console.log(`Hello, ${name}!`);
}

greet();         // "Hello, World!"
greet("Alice");  // "Hello, Alice!"