JavaScript Interview Questions

30 essential JavaScript questions covering closures, promises, prototypes, and ES6+ features. Perfect for screening frontend developers.

MEDIUM7 questions12 minProgramming

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1.What is the output of typeof null in JavaScript?

null

object

undefined

string

EASYMultiple Choice

2.What is a closure in JavaScript?

A function that retains access to its outer scope even after the outer function has returned

A function that is immediately invoked after definition

A method that closes browser windows via script

A way to make variables private using the private keyword

MEDIUMMultiple Choice

3.What is the difference between let, const, and var?

var is function-scoped; let and const are block-scoped; const prevents reassignment

They are identical but introduced in different ES versions

let allows reassignment while var does not

const makes the value immutable including nested properties

EASYMultiple Choice

+ 4 more questions included in the full template