JavaScript Interview Questions 2026
A current, 2026 snapshot of the JavaScript interview questions worth knowing — kept up to date as frameworks and best practices evolve, so you prepare with what companies are actually asking in 2026.
98Questions14Beginner15Intermediate69Senior
98 JavaScript questions
- 1What are higher-order functions?Intermediate
- 2What is spread and rest operator?Intermediate
- 3What is destructuring in JS?Intermediate
- 4How does fetch API work?Intermediate
- 5What are ES modules?Intermediate
- 6What is debounce and throttle?Intermediate
- 7What is event loop?Intermediate
- 8What is prototypal inheritance?Intermediate
- 9What is the this keyword in JavaScript?Intermediate
- 10What are template literals?Beginner
- 11What is event bubbling?Beginner
- 12What is DOM manipulation?Beginner
- 13Array map, filter, reduce usageBeginner
- 14What is async vs sync execution?Beginner
- 15What are JavaScript promises?Beginner
- 16Difference between == and ===Beginner
- 17What are closures in JavaScript?Beginner
- 18What is hoisting in JavaScript?Beginner
- 19What is the difference between var, let, and const?Beginner
- 20JavaScript Interview Question 1 (Free)Beginner
- 21JavaScript Interview Question 5 (Free)Intermediate
- 22JavaScript Interview Question 4 (Free)Beginner
- 23JavaScript Interview Question 3 (Free)Senior
- 24JavaScript Interview Question 2 (Free)Intermediate
- 25How does the JavaScript event loop work?Senior
- 26What is event delegation?Intermediate
- 27Microtasks vs MacrotasksSenior
- 28Throttle vs DebounceIntermediate
- 29What are closures in JavaScript?Intermediate
- 30What is the difference between imperative and declarative programming in JS?Senior
- 31How does tree shaking work in bundlers like Webpack?Senior
- 32What is request batching in frontend systems?Senior
- 33What is hydration mismatch in React/SSR apps?Senior
- 34How does JavaScript handle module federation?Senior
- 35What is memoization and how is it implemented?Senior
- 36What is function currying in JavaScript?Senior
- 37What is the difference between synchronous and asynchronous error handling?Senior
- 38How does JavaScript handle memory management internally?Senior
- 39What is the difference between call, apply, and bind in JavaScript?Senior
- 40What are the challenges of scaling JavaScript applications?Senior
- 41How do you design a scalable API layer in frontend apps?Senior
- 42What is zero-copy optimization in JavaScript systems?Senior
- 43How do browsers optimize JavaScript execution?Senior
- 44What is the difference between monolithic and microfrontend architecture?Senior
- 45How does hydration work in modern frameworks?Senior
- 46What are design trade-offs in using serverless functions?Senior
- 47How does JavaScript handle concurrency in Node.js?Senior
- 48What is the difference between shallow and deep cloning?Senior
- 49How does JavaScript handle module caching?Senior
- 50What is reactive programming in JavaScript?Senior
- 51How does JavaScript engine (like V8) execute code?Senior
- 52What is state management at scale in frontend apps?Senior
- 53What causes reflow and repaint in browsers?Senior
- 54How do JavaScript module bundlers work?Senior
- 55What is CORS and how does it work?Senior
- 56What is event delegation and why is it useful?Senior
- 57How to design scalable frontend architecture?Senior
- 58What is Big-O complexity in JS?Senior
- 59How to handle large datasets in JS?Senior
- 60What is JavaScript concurrency model?Senior
- 61What is observables in JavaScript?Senior
- 62What is functional programming in JS?Senior
- 63What are generators in JavaScript?Senior
- 64What is async iteration?Senior
- 65How to handle authentication in JS apps?Senior
- 66What is SSR and hydration?Senior
- 67What are caching strategies in JS apps?Senior
- 68What is code splitting?Senior
- 69What is tree shaking?Senior
- 70What are JavaScript design patterns?Senior
- 71What is CSRF?Senior
- 72What is XSS and how to prevent it?Senior
- 73Explain microtasks vs macrotasksSenior
- 74What are Web Workers?Senior
- 75What are service workers?Senior
- 76What is microfrontend architecture?Senior
- 77How to optimize JavaScript performance?Senior
- 78What causes memory leaks in JavaScript?Senior
- 79JavaScript Advanced Interview Question 10Beginner
- 80JavaScript Advanced Interview Question 9Senior
- 81JavaScript Advanced Interview Question 8Intermediate
- 82JavaScript Advanced Interview Question 7Beginner
- 83JavaScript Advanced Interview Question 6Senior
- 84Explain web workers and when to use themSenior
- 85Explain V8 optimization pipelineSenior
- 86How does garbage collection work in JavaScript engines?Senior
- 87Deep dive into prototype chainSenior
- 88Explain memory leaks in SPAsSenior
- 89How does async/await work internally?Senior
- 90What happens during script parsing and compilation?Senior
- 91How does tree shaking work?Senior
- 92How do closures impact performance?Senior
- 93Event loop deep dive with examplesSenior
- 94Implement your own PromiseSenior
- 95How does module bundling work internally?Senior
- 96Explain shadow DOM and use casesSenior
- 97Cross-origin resource sharing deep diveSenior
- 98How to design a high-performance animation system?Senior
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Frequently asked questions
Are these JavaScript interview questions up to date for 2026?
Yes. This page reflects 98 JavaScript interview questions kept current with today's frameworks, tooling and interview trends, with each answer maintained and dated.
What JavaScript topics should I focus on in 2026?
Prioritise the fundamentals plus the modern patterns interviewers ask about now. Each question here includes a detailed answer, code example and common mistakes so you can target the highest-impact areas.
Are these questions free?
You can read the question and a short answer for free. A subscription unlocks the full detailed explanation, real-world example, common mistakes and follow-up questions for each one.