Questions
3 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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What is the difference between app.use() and NestJS middleware?

app.use() registers Express/Fastify middleware directly — it works but bypasses NestJS DI so it cannot inject services. NestJS middleware classes implement NestMiddleware, are decorated with @Injectable(), and are applied via configure() in a module implementing NestModule — allowing them to use injected services.

NestJS middleware with DI
Key differences:
  1. 1

    app.use() — functional middleware, no DI, registered globally.

  2. 2

    NestJS middleware — class-based, supports DI, can be scoped to specific routes.

  3. 3

    NestJS middleware can be excluded from specific routes using .exclude().

  4. 4

    Use app.use() for simple third-party middleware (helmet, cors, compression).