What is a provider in NestJS?

Difficulty: 5/10

dependency injection, custom providers, module architecture

Any class decorated with @Injectable() that can be injected via the DI container is a provider. Services, repositories, factories, helpers, and guards are all providers. They are registered in a module's providers array and instantiated by the NestJS IoC container.

The main idea of a provider is that it can be injected as a dependency. NestJS manages the lifecycle and instantiation of providers through its IoC (Inversion of Control) container.

Basic provider (service) example

Examples of providers in NestJS:

1
Services — contain business logic.
2
Repositories — handle data access.
3
Guards — handle authorization.
4
Interceptors — transform requests/responses.
5
Pipes — validate and transform input data.
6
Factories — create and configure instances.

Scenario Questions

0-2 years experience

1How would you register a simple service as a provider in a NestJS module?
2If you forget to add a provider to the module's providers array, what runtime error do you see when trying to inject it?
3Show me how you would inject a provider into a controller using constructor injection.

Follow-up Questions

What is the default lifecycle scope for a NestJS provider?
How does Nest handle circular dependencies between providers?
When would you choose a request‑scoped provider over a singleton?