What is hoisting in JavaScript?

Hoisting is JavaScript's behavior of moving variable and function declarations to the top of their scope during compilation.

Variable Hoisting:

console.log(x); // undefined (not error)
var x = 5;
// Equivalent to:
var x;
console.log(x); // undefined
x = 5;

Function Hoisting:

sayHello(); // "Hello!" - works
function sayHello() {
  console.log("Hello!");
}

let/const Hoisting:

console.log(y); // ReferenceError
let y = 10;

let and const are hoisted but not initialized, creating a "temporal dead zone".