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Top 100 JavaScript Interview Questions & Answers (2026)

100 Questions 42 Beginner 31 Intermediate 27 Advanced

About JavaScript

JavaScript is the only programming language that runs natively in web browsers, making it indispensable for web development. It has expanded to server-side development (Node.js), mobile apps (React Native), and desktop apps (Electron). Every web company — from startups to FAANG — hires JavaScript developers, making it one of the highest-demand skills in tech.

What to Expect in a JavaScript Interview

JavaScript interviews heavily test closures, prototypal inheritance, the event loop and asynchronous patterns (callbacks, Promises, async/await), ES6+ features, scope and hoisting, DOM manipulation, and `this` binding. Frontend roles add framework knowledge; Node.js roles focus on server-side patterns, streams, and performance.

How to Use This Guide

JavaScript's quirks and gotchas are a favorite interview topic. Pay special attention to questions about type coercion, hoisting, the event loop, and `this` binding — these trip up even experienced developers. The async section is critical for any modern JavaScript role.

Curated by Tech Baithak Editorial Team  ·  Last updated: May 2026

Beginner 42 questions

Core concepts every JavaScript developer must know.

01 What is JavaScript? 02 What is the difference between var, let, and const? 03 What are JavaScript data types? 04 What is the difference between == and === in JavaScript? 05 What is hoisting in JavaScript? 06 What is a closure in JavaScript? 07 What is the difference between null and undefined? 08 What is NaN in JavaScript? 09 What are truthy and falsy values in JavaScript? 10 What is the difference between function declaration and function expression? 11 What is an arrow function in JavaScript? 12 What is the this keyword in JavaScript? 13 What are template literals in JavaScript? 14 What is destructuring in JavaScript? 15 What is the spread operator in JavaScript? 16 What are JavaScript Promises? 17 What is async/await in JavaScript? 18 What is the event loop in JavaScript? 19 What is the DOM in JavaScript? 20 What are JavaScript events? 21 What is event bubbling and capturing? 22 What is localStorage and sessionStorage? 23 What is JSON in JavaScript? 24 What is the Array map() method? 25 What is the Array filter() method? 26 What is the Array reduce() method? 27 What is the difference between forEach and map? 28 What is the typeof operator? 29 What are JavaScript arrays and their methods? 30 What is the difference between slice and splice? 31 What are JavaScript objects? 32 What is the optional chaining operator? 33 What is the nullish coalescing operator? 34 What is the difference between for...in and for...of? 35 What are default parameters in JavaScript? 36 What is the difference between synchronous and asynchronous JavaScript? 37 What are JavaScript modules (import/export)? 38 What is the prototype in JavaScript? 39 What is the difference between call(), apply(), and bind()? 40 What is a callback function? 41 What is the use of the Array.from() method? 42 What is the difference between indexOf and includes?
Intermediate 31 questions

Practical knowledge for developers with hands-on experience.

01 What is the prototype chain in JavaScript? 02 What is ES6 class syntax in JavaScript? 03 What is the difference between Object.assign and the spread operator for objects? 04 What are Symbols in JavaScript? 05 What are JavaScript generators? 06 What is a WeakMap and WeakSet? 07 What is memoization in JavaScript? 08 What is currying in JavaScript? 09 What is the Event Delegation pattern? 10 What is the difference between Map and Object? 11 What is the Set object in JavaScript? 12 What is the difference between shallow and deep copy? 13 What is Promise.all() vs Promise.allSettled()? 14 What is the Fetch API? 15 What is debouncing and throttling? 16 What are iterators and the iterable protocol? 17 What is async iteration in JavaScript? 18 What is the Proxy object in JavaScript? 19 What is the Reflect API in JavaScript? 20 What is error handling in JavaScript? 21 What is scope and the scope chain in JavaScript? 22 What is the difference between synchronous and asynchronous error handling? 23 What is function composition in JavaScript? 24 What is an IIFE (Immediately Invoked Function Expression)? 25 What is the arguments object in JavaScript? 26 What is short-circuit evaluation in JavaScript? 27 What is the difference between for...in and Object.keys()? 28 What is type coercion in JavaScript? 29 What is the difference between Array.find() and Array.filter()? 30 What is the function prototype and call stack? 31 What is prototype pollution in JavaScript?
Back to All Topics 100 questions total