Backend Technologies · JavaScript / TypeScript
Fastify — Free Learning Resources
Free, printable resources for Fastify — practice problems, quick-reference cheatsheet, and an interview prep sheet. No sign-up required.
Fastify — Practice Worksheet
Structured exercises and problems to build hands-on Fastify skills. Work through key concepts step by step.
Fastify — Cheatsheet
One-page quick-reference for Fastify — key syntax, commands, patterns, and best practices at a glance.
Fastify — Interview Sheet
Top Fastify interview questions with concise answers. Get ready for any technical round with this focused prep sheet.
About Fastify
Fastify is a high-performance Node.js web framework focused on developer experience and speed. It achieves 30,000+ requests/second via schema-based JSON serialization and a low-overhead plugin architecture. Fastify's plugin system, TypeScript support, and built-in logging via Pino make it a strong choice for performance-critical APIs.
FastifyCheat Sheet — What's Covered
- ✓Plugin system — encapsulation, fastify-plugin, and scope isolation
- ✓Schema-based validation and serialization with JSON Schema
- ✓Hooks lifecycle — onRequest, preHandler, onSend, onClose
- ✓Fastify decorators for extending request, reply, and the instance
- ✓TypeScript integration and type-safe route definitions
Frequently Asked Questions — Fastify
Why is Fastify faster than Express?
Fastify uses JSON Schema to compile serializers at startup, avoiding per-request JSON.stringify overhead. Its internal request lifecycle and plugin system are designed for minimal allocations. These optimizations together yield 2-3x the throughput of Express in benchmarks.
How does Fastify's plugin system work?
Plugins are functions registered with fastify.register(). Each plugin runs in an encapsulated scope — decorators, routes, and hooks added inside are invisible outside. Use fastify-plugin to break encapsulation and share a plugin's additions with the parent scope.
How does schema validation work in Fastify?
Pass a schema object to route options: { schema: { body: { type: 'object', required: ['email'] }, response: { 200: UserSchema } } }. Fastify compiles validators with ajv at startup and returns 400 on validation failure automatically.
What are Fastify decorators?
Decorators extend the Fastify instance, request, or reply with new properties or methods: fastify.decorate('db', dbConnection). This is how database connections, authentication utilities, and shared services are attached and reused across plugins and routes.
How does Fastify handle async errors?
Fastify catches unhandled promise rejections from async route handlers automatically — no need for try/catch wrappers. Thrown errors are passed to the error handler. Define fastify.setErrorHandler() to customize how errors are serialized and logged.
Who Is This For?
Node.js developers who need maximum performance in a structured framework with built-in schema validation and a clean plugin architecture.