Interview questions
The most asked questions, for every technology
412 questions across 16 technologies, each with a clear answer, code you can run, and the follow-up interviewers usually ask next. The flames show how often a question comes up. Mark each one as known or to review, or drill them in practice mode.
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Frontend
- HTML25 questions · 8 most asked
- · What does <!DOCTYPE html> do? What happens if you leave it out?
- · What is semantic HTML and why does it matter?
14 easy · 9 medium · 2 hard
- CSS25 questions · 8 most asked
- · Explain the CSS box model.
- · What does box-sizing: border-box do, and why do most resets use it?
9 easy · 11 medium · 5 hard
- JavaScript25 questions · 11 most asked
- · What is the difference between var, let and const?
- · What is a closure? Give a real use.
12 easy · 11 medium · 2 hard
- TypeScript25 questions · 8 most asked
- · What is TypeScript and why use it over JavaScript?
- · What is the difference between interface and type?
6 easy · 15 medium · 4 hard
- React27 questions · 10 most asked
- · What is the virtual DOM and how does reconciliation work?
- · Why do list items need a key, and why is the array index a bad key?
10 easy · 15 medium · 2 hard
- Next.js23 questions · 8 most asked
- · What is Next.js and why use it instead of plain React?
- · Explain SSR vs SSG vs ISR vs CSR.
9 easy · 10 medium · 4 hard
Backend
- Node.js25 questions · 8 most asked
- · What is Node.js, and how can it be single-threaded yet handle many requests?
- · Walk me through the phases of the Node.js event loop.
12 easy · 9 medium · 4 hard
- Express & REST APIs25 questions · 9 most asked
- · How does the middleware chain and next() work in Express?
- · How does error-handling middleware work in Express?
11 easy · 12 medium · 2 hard
- Auth & Web Security25 questions · 9 most asked
- · What is the difference between authentication and authorisation?
- · Session cookies vs JWTs: how do they work and which would you choose?
8 easy · 14 medium · 3 hard
Databases
- SQL29 questions · 10 most asked
- · In what order does SQL logically execute a SELECT query?
- · What is the difference between WHERE and HAVING?
11 easy · 13 medium · 5 hard
- MongoDB26 questions · 8 most asked
- · What is MongoDB? Explain documents, collections and BSON.
- · How is MongoDB different from a SQL database? When would you choose it?
9 easy · 12 medium · 5 hard
DevOps & Tools
- Git & GitHub27 questions · 9 most asked
- · What is the difference between Git and GitHub?
- · Explain the working tree, staging area and repository.
15 easy · 10 medium · 2 hard
- Docker, CI/CD & Deployment26 questions · 9 most asked
- · What is the difference between a container and a virtual machine?
- · What is the difference between a Docker image and a container?
8 easy · 17 medium · 1 hard
- Testing23 questions · 8 most asked
- · What is the difference between unit, integration and end-to-end tests?
- · Jest vs Vitest: what are the basics of writing a test?
9 easy · 12 medium · 2 hard
Fundamentals
- System Design28 questions · 10 most asked
- · Vertical vs horizontal scaling?
- · What does a load balancer do? Which algorithms are common?
6 easy · 15 medium · 7 hard
- DSA28 questions · 15 most asked
- · What is Big-O? Give the complexity of common operations.
- · Two Sum: find indices of two numbers that add up to a target.
9 easy · 18 medium · 1 hard