Angular Web Framework Services & Dependency Injection 3

Question 1

What is an InjectionToken used for in Angular?

Accepted Answer

To create a type-safe token for non-class dependencies like strings or config objects

Answer

InjectionToken provides a unique, type-safe token for values that cannot be represented by a class, such as configuration objects, strings, or interfaces.

Question 2

Which `providers` syntax allows you to supply a pre-constructed object or primitive value directly?

Accepted Answer

{ provide: TOKEN, useValue: myObject }

Answer

useValue registers a static, pre-built value with the injector so no factory or class instantiation occurs.

Question 3

How do you declare factory dependencies when using `useFactory`?

Accepted Answer

Provide them via the `deps` array in the provider definition

Answer

The deps array in the provider object lists the tokens Angular resolves and passes as arguments to the factory function in order.

Question 4

What does the `@Optional()` decorator do when applied to a constructor parameter?

Accepted Answer

Allows the injection to resolve to null if the provider is not registered

Answer

@Optional() prevents an error when a dependency has no registered provider; Angular injects null instead of throwing.

Question 5

What is the role of the `@Self()` decorator in Angular DI?

Accepted Answer

It restricts resolution to the injector of the current element, never walking up to parent injectors

Answer

@Self() tells Angular to look for the dependency only in the host element's injector and throw if it's not found there.

Angular Web Framework Practice Test

Angular Web Framework Practice Test

Angular Web Framework Services & Dependency Injection 3