What is a Provider

A provider is a registration rule that tells the container how to resolve a token.

Why Providers Matter

• They make service graphs explicit.
• They enable local overrides in child modules.
• They improve testability by allowing token-level replacement.

Provider Forms

1. Constructor provider (MyService)
2. useClass ({ provide, useClass })
3. useValue ({ provide, useValue })
4. useFactory ({ provide, useFactory, inject? })
5. useExisting ({ provide, useExisting })

Scope Behavior

Scope controls instance lifetime:

• singleton
• transient
• containerScoped
• resolutionScoped (except useFactory)

Lifecycle and Providers

Providers that resolve to objects implementing:

• onModuleInit
• onModuleMount
• onModuleUnmount
• onModuleDestroy

are automatically included in provider lifecycle execution for owned modules.

useExisting providers are excluded from lifecycle token collection to avoid duplicate lifecycle calls through alias tokens.

Where Providers Are Used

• ModuleProvider accepts providers and registers them in module scope.
• Child modules can shadow parent tokens.

Next: Provider Registration, Resolver, Async Teardown