Fullstack Developer Interview Questions

The definitive guide for full-stack engineers, covering Frontend (React, Next.js, TypeScript), Backend (Node.js, Express), Databases (SQL/NoSQL), System Design, and DevOps.

Total Questions:510
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1.What is the difference between var, let, and const?

2.Explain hoisting in JavaScript with examples.

3.What is the difference between == and === in JavaScript?

4.What are closures in JavaScript and why are they useful?

5.Explain the concept of 'this' keyword in JavaScript.

6.What is the difference between null and undefined?

7.What are arrow functions and how do they differ from regular functions?

8.What is the difference between function declaration and function expression?

9.Explain call, apply, and bind methods.

10.What is the event loop in JavaScript?

11.What are promises in JavaScript?

12.What is the difference between Promise.all() and Promise.race()?

13.What is async/await and how does it work?

14.What is callback hell and how do you avoid it?

15.What are higher-order functions in JavaScript?

16.Explain map, filter, and reduce with examples.

17.What is the difference between slice() and splice()?

18.What is destructuring in JavaScript?

19.What are template literals in JavaScript?

20.What is the spread operator and rest parameters?

21.What is the difference between shallow copy and deep copy?

22.How do you clone an object in JavaScript?

23.What is prototypal inheritance in JavaScript?

24.What is the prototype chain?

25.What are JavaScript classes and how do they work?

26.What is the difference between classical and prototypal inheritance?

27.What are JavaScript modules (import/export)?

28.What is the difference between CommonJS and ES6 modules?

29.What is event bubbling and event capturing?

30.How do you stop event propagation?

31.What is event delegation?

32.What are Web Workers in JavaScript?

33.What is the difference between localStorage and sessionStorage?

34.What are cookies and how do they differ from storage APIs?

35.What is CORS (Cross-Origin Resource Sharing)?

36.How do you handle errors in JavaScript?

37.What is try-catch-finally block?

38.What are custom errors in JavaScript?

39.What is strict mode in JavaScript?

40.What are generator functions in JavaScript?

41.What is debouncing and throttling?

42.How do you implement debouncing in JavaScript?

43.What is memoization and how do you implement it?

44.What are WeakMap and WeakSet?

45.What is the difference between Map and Object?

46.What are Symbols in JavaScript?

47.What are iterators and iterables?

48.What is the for...of loop vs for...in loop?

49.What is currying in JavaScript?

50.What is function composition?

51.What are pure functions?

52.What is immutability and why is it important?

53.What is the difference between synchronous and asynchronous code?

54.What are microtasks and macrotasks?

55.What is the JavaScript runtime environment?

56.What is garbage collection in JavaScript?

57.What are memory leaks and how do you prevent them?

58.What is the difference between shallow and deep comparison?

59.How do you implement a custom Promise?

60.What is Proxy in JavaScript?

61.What is TypeScript and why should you use it?

62.What are the benefits of using TypeScript over JavaScript?

63.What are types in TypeScript?

64.What is the difference between type and interface?

65.What are union types and intersection types?

66.What are generics in TypeScript?

67.What is type inference in TypeScript?

68.What are type guards in TypeScript?

69.What is the 'any' type and why should you avoid it?

70.What is the 'unknown' type vs 'any' type?

71.What are enums in TypeScript?

72.What are tuple types in TypeScript?

73.What is the 'never' type in TypeScript?

74.What are optional properties in TypeScript?

75.What is the 'readonly' modifier?

76.What are access modifiers (public, private, protected)?

77.What are abstract classes in TypeScript?

78.What is type assertion in TypeScript?

79.What are utility types (Partial, Pick, Omit, etc.)?

80.How do you handle null and undefined in TypeScript?

81.What is React and why is it popular?

82.What are React components?

83.What is the difference between functional and class components?

84.What are React Hooks?

85.What is useState hook and how do you use it?

86.What is useEffect hook and when is it called?

87.What is the dependency array in useEffect?

88.What is the difference between useEffect and useLayoutEffect?

89.What is useContext hook?

90.What is useReducer and when should you use it?

91.What is the difference between useState and useReducer?

92.What is useMemo and when should you use it?

93.What is useCallback and how does it differ from useMemo?

94.What is useRef hook used for?

95.What are custom hooks in React?

96.What is the Virtual DOM in React?

97.How does React reconciliation work?

98.What is JSX in React?

99.What are props in React?

100.What is prop drilling and how do you avoid it?

101.What is the Context API in React?

102.What is Redux and why is it used?

103.What are Redux actions, reducers, and store?

104.What is the difference between Redux and Context API?

105.What is Redux Toolkit?

106.What are Redux middleware (thunk, saga)?

107.What is the difference between Redux Thunk and Redux Saga?

108.What is component lifecycle in React?

109.What are lifecycle methods in class components?

110.How do you handle forms in React?

111.What is controlled vs uncontrolled components?

112.What is React Router and how does it work?

113.What is the difference between Link and NavLink in React Router?

114.How do you implement protected routes in React?

115.What is lazy loading in React?

116.What is code splitting in React?

117.What is React.memo() and when should you use it?

118.What is PureComponent in React?

119.What are React Fragments?

120.What is the key prop in React lists and why is it important?

121.What is Server-Side Rendering (SSR) in React?

122.What is Next.js and its benefits?

123.What is Static Site Generation (SSG) vs Server-Side Rendering?

124.What is Incremental Static Regeneration (ISR)?

125.What are React Portals?

126.What are Error Boundaries in React?

127.What is Suspense in React?

128.What is React Concurrent Mode?

129.What are Higher-Order Components (HOC)?

130.What are Render Props in React?

131.What is the Compound Component pattern?

132.What is React Testing Library?

133.How do you test React components?

134.What is snapshot testing in React?

135.What is the difference between shallow and mount in Enzyme?

136.How do you optimize React performance?

137.What causes re-renders in React?

138.How do you prevent unnecessary re-renders?

139.What is React Profiler?

140.What is the difference between useEffect cleanup and componentWillUnmount?

141.What is Node.js and why is it used for backend?

142.What is the event-driven architecture in Node.js?

143.What is non-blocking I/O in Node.js?

144.What is the difference between Node.js and browser JavaScript?

145.What is the Node.js event loop?

146.What are streams in Node.js?

147.What is the difference between readable and writable streams?

148.What is the Buffer in Node.js?

149.What is the difference between process.nextTick() and setImmediate()?

150.What is clustering in Node.js?

151.What is the child_process module?

152.What is Express.js?

153.What is middleware in Express?

154.What are the types of middleware in Express?

155.What is the difference between app.use() and app.get()?

156.How do you handle errors in Express?

157.What is body-parser middleware?

158.What is CORS middleware and why is it needed?

159.What is helmet middleware for security?

160.How do you serve static files in Express?

161.What is routing in Express?

162.What are route parameters and query parameters?

163.How do you handle file uploads in Node.js?

164.What is Multer middleware?

165.How do you implement authentication in Express?

166.What is JWT (JSON Web Token)?

167.What is the difference between session-based and token-based authentication?

168.How do you implement refresh tokens?

169.What is bcrypt and why is it used?

170.How do you hash passwords in Node.js?

171.What is the crypto module in Node.js?

172.What is environment variable management (.env file)?

173.What is dotenv package?

174.How do you handle asynchronous operations in Node.js?

175.What is the difference between callbacks and promises in Node.js?

176.What is async/await in Node.js?

177.How do you prevent callback hell in Node.js?

178.What is npm and yarn?

179.What is the difference between npm and yarn?

180.What is package.json and package-lock.json?

181.What is a relational database?

182.What is SQL and its types (DDL, DML, DCL, TCL)?

183.What is the difference between SQL and NoSQL databases?

184.What are primary keys and foreign keys?

185.What is normalization in databases?

186.What are the normal forms (1NF, 2NF, 3NF, BCNF)?

187.What is denormalization and when should you use it?

188.What is an index in a database?

189.What are the types of indexes?

190.What is the difference between clustered and non-clustered indexes?

191.What are database constraints (NOT NULL, UNIQUE, CHECK)?

192.What is the difference between DELETE, TRUNCATE, and DROP?

193.What are SQL JOINs and their types?

194.What is the difference between INNER JOIN and OUTER JOIN?

195.What is a LEFT JOIN vs RIGHT JOIN?

196.What is a CROSS JOIN?

197.What is a self-join?

198.What are subqueries in SQL?

199.What is the difference between WHERE and HAVING clause?

200.What are aggregate functions (COUNT, SUM, AVG, MIN, MAX)?

201.What is GROUP BY clause?

202.What is the ORDER BY clause?

203.What are window functions in SQL?

204.What is the difference between UNION and UNION ALL?

205.What are views in SQL?

206.What is a stored procedure?

207.What is the difference between stored procedure and function?

208.What are triggers in databases?

209.What is a database transaction?

210.What are ACID properties in databases?

211.What is the difference between COMMIT and ROLLBACK?

212.What is database locking?

213.What are deadlocks and how do you prevent them?

214.What is connection pooling in databases?

215.What is PostgreSQL and how does it differ from MySQL?

216.What are the advantages of PostgreSQL over MySQL?

217.What is the difference between VARCHAR and TEXT?

218.What is EXPLAIN in SQL query optimization?

219.How do you optimize slow SQL queries?

220.What is database replication?

221.What is MongoDB and why is it used?

222.What is a document in MongoDB?

223.What is a collection in MongoDB?

224.What is the difference between SQL and MongoDB queries?

225.What is the _id field in MongoDB?

226.What are MongoDB operators ($gt, $lt, $in, etc.)?

227.What is the aggregation pipeline in MongoDB?

228.What are the stages in MongoDB aggregation?

229.What is indexing in MongoDB?

230.What are the types of indexes in MongoDB?

231.What is sharding in MongoDB?

232.What is replication in MongoDB?

233.What is a replica set in MongoDB?

234.What is the difference between embedding and referencing in MongoDB?

235.When should you embed vs reference documents?

236.What is Mongoose in Node.js?

237.What are Mongoose schemas and models?

238.What are Mongoose middleware (pre and post hooks)?

239.What is population in Mongoose?

240.What are Mongoose virtuals?

241.How do you perform validation in Mongoose?

242.What is the difference between findOne() and find()?

243.What is the difference between updateOne() and findOneAndUpdate()?

244.What are MongoDB transactions?

245.What is Redis and when should you use it?

246.What is the difference between Redis and MongoDB?

247.What are Redis data structures?

248.What is caching and how does Redis help?

249.What is Cassandra database?

250.What is DynamoDB?

301.What is salt in password hashing?

302.What is HTTPS and how does it work?

303.What is SSL/TLS?

304.What are SSL certificates?

305.What is Content Security Policy (CSP)?

306.What is helmet.js for Express security?

307.What are secure HTTP headers?

308.What is the Same-Origin Policy?

309.How do you store sensitive data securely?

310.What is environment variable security?

311.What is CI/CD (Continuous Integration/Continuous Deployment)?

312.What is Git and why is it important?

313.What is the difference between Git and GitHub?

314.What are Git branches?

315.What is the difference between merge and rebase?

316.What is a pull request?

317.What is Git flow?

318.What is Docker and why is it used?

319.What is a Docker container?

320.What is the difference between Docker image and container?

321.What is Dockerfile?

322.What is docker-compose?

323.What is the difference between Docker and Virtual Machine?

324.What is Kubernetes?

325.What is a Kubernetes pod?

326.What is container orchestration?

327.What is AWS and its core services?

328.What is EC2 in AWS?

329.What is S3 in AWS?

330.What is AWS Lambda?

331.What is serverless architecture?

332.What are the benefits of serverless?

333.What is Elastic Beanstalk?

334.What is AWS RDS?

335.What is the difference between RDS and DynamoDB?

336.What is CloudFront CDN?

337.What is Nginx and why is it used?

338.What is the difference between Nginx and Apache?

339.What is a reverse proxy?

340.What is load balancing?

341.What is unit testing?

342.What is integration testing?

343.What is end-to-end (E2E) testing?

344.What is the difference between unit and integration testing?

345.What is Test-Driven Development (TDD)?

346.What is Jest testing framework?

347.How do you write unit tests in JavaScript?

348.What are test suites and test cases?

349.What is mocking in testing?

350.What is the difference between mock, stub, and spy?

351.What is code coverage?

352.What is a good code coverage percentage?

353.What is Mocha testing framework?

354.What is Chai assertion library?

355.What is Supertest for API testing?

356.How do you test asynchronous code?

357.What is snapshot testing?

358.What is Cypress for E2E testing?

359.What is Selenium?

360.What is the difference between Cypress and Selenium?

361.What is lazy loading?

362.What is code splitting?

363.What is tree shaking?

364.What is minification and uglification?

365.What is bundling in web development?

366.What is Webpack?

367.What is the difference between Webpack and Vite?

368.What is server-side rendering (SSR)?

369.What is client-side rendering (CSR)?

370.What is the difference between SSR and CSR?

371.What is hydration in SSR?

372.What is prefetching and preloading?

373.What is caching and its types?

374.What is browser caching?

375.What are cache headers (Cache-Control, ETag)?

376.What is CDN (Content Delivery Network)?

377.What is image optimization?

378.What is WebP image format?

379.What is responsive images (srcset)?

380.What is database query optimization?

381.What is N+1 query problem?

382.How do you solve N+1 query problem?

383.What is pagination vs infinite scroll?

384.What is database indexing for performance?

385.What is connection pooling?

386.What is API response caching?

387.What is Redis for caching?

388.What is memoization in frontend?

389.What are Web Workers for performance?

390.What is throttling and debouncing for performance?

391.What is WebSocket protocol?

392.What is the difference between HTTP and WebSocket?

393.What is Socket.io?

394.How do you implement real-time chat using Socket.io?

395.What are Socket.io rooms and namespaces?

396.What is the difference between polling and WebSockets?

397.What is long polling?

398.What is Server-Sent Events (SSE)?

399.When should you use WebSocket vs SSE?

400.How do you handle WebSocket reconnection?

401.What is monolithic architecture?

402.What is microservices architecture?

403.What are the advantages of microservices?

404.What are the challenges of microservices?

405.What is service discovery in microservices?

406.What is API Gateway?

407.What is message queue?

408.What is RabbitMQ?

409.What is Apache Kafka?

410.What is the difference between RabbitMQ and Kafka?

411.What is event-driven architecture?

412.What is CQRS (Command Query Responsibility Segregation)?

413.What is event sourcing?

414.What is database per service pattern?

415.What is distributed transactions?

416.What is the Saga pattern?

417.What is circuit breaker pattern?

418.What is service mesh?

419.What is Istio?

420.What is horizontal vs vertical scaling?

421.How would you design a URL shortener like bit.ly?

422.How would you implement a rate limiter?

423.How would you design a real-time notification system?

424.How would you implement infinite scroll in a social media feed?

425.How would you build a file upload system with progress tracking?

426.How would you implement search functionality with autocomplete?

427.How would you design a shopping cart system?

428.How would you implement a payment gateway integration?

429.How would you build a multi-tenant SaaS application?

430.How would you implement user roles and permissions?

431.How would you design a content management system (CMS)?

432.How would you implement a blog with comments system?

433.How would you build a real-time collaborative editor like Google Docs?

434.How would you implement email verification system?

435.How would you design a video streaming platform?

436.How would you implement a recommendation engine?

437.How would you build a dashboard with real-time analytics?

438.How would you implement data export functionality (CSV, PDF)?

439.How would you design a booking/reservation system?

440.How would you implement a queue system for background jobs?

441.How would you handle large file uploads (>1GB)?

442.How would you implement a search feature with filters?

443.How would you build an admin panel for managing users?

444.How would you implement audit logging?

445.How would you design a multi-language application?

446.How would you implement data migration between databases?

447.How would you build a REST API with versioning?

448.How would you implement soft delete functionality?

449.How would you handle timezone conversions in a global app?

450.How would you implement a forgot password flow?

451.Design YouTube's video recommendation system

452.How would you scale Google Search to handle billions of queries?

453.Design Google Drive's file sharing architecture

454.Implement Google Docs real-time collaboration

455.Design Gmail's email filtering system

456.Design Facebook's newsfeed architecture

457.How would you implement Instagram's story feature?

458.Design a distributed like/comment system

459.How would you scale Facebook Messenger?

460.Implement real-time notifications for millions of users

461.Design Amazon's product search and filtering

462.How would you implement Amazon's shopping cart?

463.Design the order tracking system

464.How would you implement Amazon's recommendation engine?

465.Design a scalable inventory management system

466.Design Netflix's video streaming architecture

467.How would you implement continue watching feature?

468.Design a recommendation algorithm for movies

469.How would you handle video encoding for multiple devices?

470.Implement a distributed caching system for videos

471.Design Uber's ride matching system

472.How would you implement real-time driver location tracking?

473.Design surge pricing algorithm

474.How would you handle ride cancellations?

475.Implement a trip fare calculation system

476.Design Airbnb's search and booking system

477.How would you implement calendar availability?

478.Design the review and rating system

479.How would you handle payment processing?

480.Implement a recommendation system for properties

481.Design Twitter's timeline architecture

482.How would you implement trending topics?

483.Design the tweet search functionality

484.How would you scale Twitter to handle millions of tweets?

485.Implement real-time follower count updates

486.Design Spotify's music recommendation system

487.How would you implement playlist collaboration?

488.Design offline music playback

489.How would you handle music streaming with quality adjustment?

490.Implement a shuffle algorithm that feels random

491.Design LinkedIn's connection recommendation system

492.How would you implement job search with filters?

493.Design the messaging system

494.How would you calculate profile strength?

495.Implement a feed ranking algorithm

496.Design a payment processing system

497.How would you handle payment failures and retries?

498.Design a subscription billing system

499.How would you implement refunds?

500.Design a fraud detection system

501.Tell me about a challenging bug you fixed

502.How do you handle disagreements with team members?

503.Describe a time you had to learn a new technology quickly

504.How do you prioritize tasks when everything is urgent?

505.Tell me about a project you're most proud of

506.How do you stay updated with new technologies?

507.Describe a time you optimized application performance

508.How do you handle technical debt?

509.What's your approach to code reviews?

510.How do you ensure code quality in your projects?