Functions

Function Declaration

A function declaration defines a named function that is hoisted to the top of its scope.

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

console.log(greet("Alice")); // Hello, Alice!
console.log(greet("Bob"));   // Hello, Bob!

Function declarations are hoisted, meaning you can call them before they appear in the code.

console.log(double(5)); // 10

function double(n) {
  return n * 2;
}

A function expression assigns a function to a variable. These are not hoisted.

const multiply = function(a, b) {
  return a * b;
};

console.log(multiply(4, 3)); // 12

Function expressions are useful when you need to pass a function as an argument or assign it conditionally.

Functions without a name are called anonymous. They are often used as callbacks.

const numbers = [1, 2, 3, 4];
const tripled = numbers.map(function(n) {
  return n * 3;
});
console.log(tripled); // [3, 6, 9, 12]

An IIFE runs as soon as it is defined, creating a private scope.

(function() {
  const secret = "This is private";
  console.log(secret);
})();
// secret is not accessible outside