What hoisting is in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is hoisting in JavaScript?

Hoisting is JavaScript's behavior of moving variable and function declarations to the top of their containing scope before code execution.

beginner

How does hoisting affect variable declarations with var?

Variables declared with var are hoisted and initialized with undefined, so you can use them before their declaration without a ReferenceError, but their value will be undefined until assigned.

intermediate

Are let and const variables hoisted in JavaScript?

Yes, let and const declarations are hoisted but not initialized. Accessing them before declaration causes a ReferenceError due to the 'temporal dead zone'.

beginner

How are function declarations treated during hoisting?

Function declarations are fully hoisted, meaning the entire function is moved to the top of the scope, so you can call the function before its declaration in the code.

intermediate

What happens if you try to use a function expression before it is defined?

Function expressions assigned to variables are hoisted only as variable declarations (with var hoisted as undefined). Calling the function before assignment results in an error because the variable is not yet a function.

What does hoisting do in JavaScript?

A Moves declarations to the top of their scope before execution

B Runs code faster by optimizing loops

C Prevents variables from being used before declaration

D Automatically initializes variables with default values

Hoisting moves variable and function declarations to the top of their scope before the code runs.

What value does a var variable have if accessed before its declaration?

A undefined

B The assigned value

C null

D ReferenceError

var variables are hoisted and initialized with undefined.

What happens if you access a let variable before its declaration?

A Returns undefined

B Returns null

C Throws ReferenceError

D Returns 0

let variables are hoisted but not initialized, causing a ReferenceError if accessed early.

Can you call a function declared with function keyword before its declaration?

A No, it causes a ReferenceError

B Yes, because function declarations are hoisted

C Only if declared with <code>var</code>

D Only if declared with <code>let</code>

Function declarations are fully hoisted, so you can call them before their code line.

What happens if you call a function expression assigned to a var variable before assignment?

A Function runs normally

B Returns undefined

C Throws ReferenceError

D Throws TypeError

The variable is hoisted as undefined, so calling it as a function causes a TypeError.

Explain hoisting in JavaScript and how it affects variables declared with var, let, and const.

Think about where declarations move before code runs and how accessing variables early behaves.

Describe the difference between hoisting of function declarations and function expressions.

Consider how the entire function or just the variable name moves up.