Questions

4 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 a service and a repository in NestJS?

A service contains business logic and orchestrates calls to repositories, other services, or external APIs. A repository is a data-access abstraction that handles persistence concerns such as queries and transactions. Services are injected with repositories — this keeps business logic and data access cleanly separated.

Service using an injected repository

Separation of concerns:

1
Service — owns business rules, validation logic, and orchestration.
2
Repository — owns data access: queries, inserts, updates, transactions.
3
This separation makes services easier to unit test (mock the repository).
4
TypeORM provides Repository<Entity> via @InjectRepository() out of the box.