What is a shared module in NestJS?

Q: What is a shared module in NestJS?

// Shared module — exports what consumers need @Module({ providers: [CryptoService, HashService], exports: [CryptoService, HashService], }) export class CryptoModule {} // Two different feature modules both use CryptoService @Module({ imports: [CryptoModule] }) export class AuthModule {} @Module({ imports: [CryptoModule] }) export class UsersModule {} No special decorator — any module with a populated exports array is effectively a shared module. Consumers must explicitly import it — dependencies are visible and traceable. Singleton instances — all importers share the same provider objects. Typical examples: CryptoModule, MailModule, HttpClientModule, PaginationModule.

Difficulty: 5/10

module reusability, dependency injection, circular dependencies

A shared module is a regular module that exports providers so multiple other modules can use them. There is no special decorator — it is just a module with a well-defined exports array. Any module that needs its providers must explicitly import it. Because modules are singletons, all consumers share the same provider instances.

Shared module used by multiple feature modules

Key characteristics of a shared module:

1
No special decorator — any module with a populated exports array is effectively a shared module.
2
Consumers must explicitly import it — dependencies are visible and traceable.
3
Singleton instances — all importers share the same provider objects.
4
Typical examples: CryptoModule, MailModule, HttpClientModule, PaginationModule.

Scenario Questions

0-2 years experience

2-5 years experience

1During a sprint we added a new PaymentsModule that also needs the same ConfigService used by existing modules. After moving ConfigService into a SharedModule, the PaymentsModule fails to get the correct environment variables. What could be causing this and how would you fix it?

Follow-up Questions