What is a shared module in NestJS?
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:
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.