Questions
8 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 resolve a provider when the same token is exported by two different imported modules?

The last provider registered for a given token wins. NestJS uses the order of the imports array to determine precedence — the module listed later takes priority. This silent shadowing is a common source of bugs and is best prevented by using unique namespaced tokens such as Symbols or InjectionToken.

Token collision — last import wins
How to prevent token collision:
  1. 1

    Use Symbol() or InjectionToken for all non-class provider tokens — they are inherently unique.

  2. 2

    Namespace string tokens with the module name: 'AuthModule.JwtSecret' not just 'JwtSecret'.

  3. 3

    Avoid having two modules export providers under the same token.

  4. 4

    Document which module is the authoritative source for shared infrastructure tokens.

  5. 5

    Token shadowing is silent — there are no warnings at startup, only wrong behavior at runtime.