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Interview Questions & Tips
Common Fastify questions asked in interviews.
Quick check: Why is Fastify faster than Express?
- It uses a different programming language
- It has lower overhead through object pooling, efficient routing, and built-in validation
- It doesn't support middleware
Answer
It has lower overhead through object pooling, efficient routing, and built-in validation — Fastify reuses request/reply objects, optimizes routing with a trie-based router, and validates input with JSON Schema—all designed for performance.
Quick check: What is the purpose of Fastify plugins?
- To add CSS styling to routes
- To encapsulate and reuse functionality (auth, DB, logging) across routes
- To replace Express middleware
Answer
To encapsulate and reuse functionality (auth, DB, logging) across routes — Plugins enable modular, maintainable code by separating concerns and allowing reusable components to be registered across the app.
Quick check: How does Fastify handle async/await in route handlers?
- It wraps them in try/catch automatically
- It catches rejected promises and passes errors to the error handler
- Async handlers are not supported
Answer
It catches rejected promises and passes errors to the error handler — Fastify is built on async/await and automatically catches rejected promises, routing them to the setErrorHandler.