angular-di

Angular dependency injection uses the inject() function and provider configurations to supply class instances to components. Providers define how tokens map to instances, while inject() retrieves those dependencies during component or service instantiation.

You configure provider scopes by registering dependencies at the root, component, or route level. Setting providedIn: 'root' creates a singleton service, while component-level providers generate separate instances for each component.

Injection tokens are unique identifiers used to register and retrieve non-class dependencies in Angular's DI system. You need them when configuring provider scopes for interfaces, custom configurations, or mocking service replacements during testing.

Yes, Angular dependency injection supports advanced patterns like state services, repository implementations, and service facades. You can use hierarchical injection to isolate state and inject data repositories into specific route components.

The best way to test Angular dependency injection configurations is by overriding providers in the testing module. You can supply mock services using injection tokens to isolate components and validate dependency scoping behavior.

An Angular service instantiates multiple times when it is provided at the component or route level instead of the root. To enforce a singleton, register the provider scope using providedIn: 'root' in the service's @Injectable decorator.