Fastify

Fastify interviews cover encapsulated plugins, JSON schema validation, hooks, decorators, and performance-oriented defaults—often as a contrast to Express minimalism.

Subtopics: plugins and encapsulation, schema validation, and the performance model.

On interviews: explain plugin scopes, how schemas validate and serialize responses, and what you would measure before claiming Fastify is faster for your app.

Common pitfalls: breaking encapsulation with global decorators, schemas that drift from real handlers, and performance claims without profiling your workload.

The trade-off is balancing simplicity, performance, safety, and operability — name which axis you optimized and what cost you accepted.

Checklist:

• Register plugins with explicit dependencies and prefixes.
• Validate inputs and serialize outputs with schemas.
• Use hooks for cross-cutting concerns inside encapsulation.
• Benchmark your routes, not generic hello-world demos.