Questions
5 of 12
1How do you apply global middleware, pipes, guards, or interceptors in NestJS?
2What is the APP_GUARD / APP_PIPE token pattern in NestJS?
3What is the difference between app.use() and NestJS middleware?
4What is the difference between a service and a repository in NestJS?
5How does NestJS achieve platform agnosticism between Express and Fastify?
6How does the NestJS bootstrap sequence work?
7What is a barrel module in NestJS and when does it become an anti-pattern?
8How does NestJS resolve a provider when the same token is exported by two different imported modules?
9How do you implement a plugin system using dynamic modules in NestJS?
10How does NestJS handle module initialization order and can you control it?
11How do you unit-test a module that uses a dynamic module dependency in NestJS?
12What is the difference between a monorepo and a standard NestJS project structure?
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How does NestJS achieve platform agnosticism between Express and Fastify?

NestJS wraps the underlying HTTP framework behind an HttpAdapter interface. Core functionality like DI, decorators, and lifecycle is framework-independent. The adapter translates NestJS abstractions to Express or Fastify internals. You switch platforms by passing a different adapter to NestFactory.create() with no application code changes.

Switching from Express to Fastify
How platform agnosticism works:
  1. 1

    NestJS defines an AbstractHttpAdapter interface that both Express and Fastify implement.

  2. 2

    Controllers, guards, interceptors, and pipes work identically on both platforms.

  3. 3

    Only platform-specific code (e.g., using @Req(), @Res() directly) breaks portability.

  4. 4

    Fastify is significantly faster than Express but has a smaller ecosystem of middleware.