18Software Engineering · Interview Prep · Free
TypeScript Developer interview questions — and how to answer them.
These are the questions TypeScript Developer candidates are most likely to face, from openers to the hard ones — each with a note on what a strong answer covers. Want more, tuned to your level? Use the free generator below.
What interviewers look for in a TypeScript Developer
- Concrete examples of systems you've built, with the trade-offs you weighed
- How you debug — the process, not just the fix
- Collaboration signals: code review, disagreements, mentoring
Likely TypeScript Developer interview questions
1. What experience do you have with TypeScript, and what made you transition from JavaScript?
Demonstrates understanding of TypeScript benefits (type safety, tooling) and practical experience with the language.
2. Explain the difference between interfaces and types in TypeScript.
Shows grasp of core TypeScript concepts; mention declaration merging, extensibility, and when to use each.
3. Tell me about a time you debugged a complex type-related issue. How did you approach it?
Reveals problem-solving methodology, familiarity with TypeScript compiler errors, and debugging tools.
4. How do you handle async/await and Promise types in TypeScript?
Covers practical async patterns, generic typing with Promise<T>, error handling with try-catch.
5. What are generics, and can you provide a real-world use case where you've implemented them?
Demonstrates understanding of reusable, type-safe code; mention constraints, extends, keyof patterns.
6. Describe your experience with a REST API or GraphQL client in TypeScript. How did types improve development?
Shows integration with external systems, API typing patterns, request/response modeling.
7. How do you approach writing unit tests for TypeScript code? What tools do you use?
Covers Jest/Vitest/Mocha, mocking strategies, type-safe test patterns, and testing best practices.
8. Explain the purpose of decorators and where you've used them in production code.
Demonstrates understanding of experimental features, dependency injection, metadata reflection, real-world use cases.
9. How do you manage and prevent type errors at runtime, especially with external data?
Covers validation libraries (Zod, io-ts), type guards, type narrowing, defensive programming strategies.
10. Walk me through how you'd refactor a large JavaScript codebase to TypeScript incrementally.
Shows strategic thinking about `allowJs`, tsconfig settings, migration priorities, and team communication.
11. Describe a situation where TypeScript's type system caught a bug before it reached production.
Illustrates appreciation for type safety, understanding of static analysis, and concrete business impact.
12. How do you optimize TypeScript build performance in a large monorepo, and what trade-offs have you made?
Covers build tools (tsc, esbuild, webpack), incremental compilation, tsconfig optimization, and architectural decisions.
Want to practice answering live with scored feedback? Try the Mock Interview Coach. Applying too? See a TypeScript Developer cover letter example.
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