Functions¶

Functions are reusable blocks of code that perform specific tasks. You define them once and call them anywhere.

1. Function Declaration¶

function greet() {
  console.log("Hello");
}

greet(); // Call the function

2. Parameters & Arguments¶

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

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

a, b → parameters (placeholders)
5, 3 → arguments (actual values)

3. Return Value¶

Use return to send a value back.

function multiply(x, y) {
  return x * y;
}

If no return, the function returns undefined.

4. Function Expression¶

Function stored in a variable.

const greet = function () {
  console.log("Hi");
};

greet();

5. Arrow Functions (ES6)¶

Shorter syntax, often used for callbacks.

const add = (a, b) => a + b;

With multiple lines:

const greet = () => {
  console.log("Hello");
};

6. Default Parameters¶

function sayHello(name = "Guest") {
  console.log("Hello, " + name);
}

sayHello(); // "Hello, Guest"

7. Rest Parameters¶

Combines multiple arguments into an array.

function sum(...nums) {
  return nums.reduce((a, b) => a + b);
}

sum(1, 2, 3); // 6

## 8. Anonymous Functions

Functions without a name, often used inline.

```js
setTimeout(function () {
  console.log("Delayed");
}, 1000);

9. Callback Functions¶

Function passed as an argument to another function.

function process(data, callback) {
  callback(data);
}

process(5, function (num) {
  console.log(num * 2);
});