JavaScript Interview Question #8

What is hoisting in JavaScript?

JavaScript Fundamentals, Types, Scope & Functions Junior Beginner

Quick Interview Answer

Hoisting describes how JavaScript processes declarations before executing code in a scope. Function declarations can generally be called before their textual declaration. var declarations are hoisted and initialized with undefined.

Detailed Explanation

let, const, and class declarations are also associated with their scope before execution, but they remain inaccessible until their declaration is evaluated. Accessing them during this period causes a ReferenceError because of the temporal dead zone.

Code Example

sayHello(); // Works

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

console.log(value); // undefined
var value = 10;

// console.log(count); // ReferenceError
let count = 5;