Services & Dependency Injection Flashcards
7 cards from real Angular Web Framework practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Services & Dependency Injection flashcards as text
What is an InjectionToken used for in Angular?
Answer: To create a type-safe token for non-class dependencies like strings or config objects
InjectionToken provides a unique, type-safe token for values that cannot be represented by a class, such as configuration objects, strings, or interfaces.
Which `providers` syntax allows you to supply a pre-constructed object or primitive value directly?
Answer: { provide: TOKEN, useValue: myObject }
useValue registers a static, pre-built value with the injector so no factory or class instantiation occurs.
How do you declare factory dependencies when using `useFactory`?
Answer: Provide them via the `deps` array in the provider definition
The deps array in the provider object lists the tokens Angular resolves and passes as arguments to the factory function in order.
What does the `@Optional()` decorator do when applied to a constructor parameter?
Answer: Allows the injection to resolve to null if the provider is not registered
@Optional() prevents an error when a dependency has no registered provider; Angular injects null instead of throwing.
What is the role of the `@Self()` decorator in Angular DI?
Answer: It restricts resolution to the injector of the current element, never walking up to parent injectors
@Self() tells Angular to look for the dependency only in the host element's injector and throw if it's not found there.
Which class-level `providers` option in @Component creates a new service instance for every component instance?
Answer: providers: [MyService] inside @Component metadata
Adding a service to a component's providers array causes Angular to create a fresh instance scoped to that component and its subtree.
What is the difference between `providers` and `viewProviders` in an Angular component?
Answer: viewProviders are visible only to the component's own view, not to projected content (ng-content)
Services in viewProviders are not accessible from content projected via ng-content, whereas providers are visible to both the component's view and projected content.