Angular Web Framework Services & Dependency Injection 4

Question 1

What does `providedIn: 'any'` do in Angular's @Injectable decorator?

Accepted Answer

Creates a separate singleton instance for each lazy-loaded module that injects it

Answer

providedIn: 'any' gives each lazy-loaded module its own singleton while all eagerly loaded code shares one instance.

Question 2

In Angular's hierarchical injection system, what happens when an injector cannot find a requested token?

Accepted Answer

It throws a NullInjectorError

Answer

When no injector in the hierarchy can satisfy a token and no @Optional() is present, Angular throws a NullInjectorError.

Question 3

Which Angular injector level sits above the root (AppModule) injector?

Accepted Answer

Platform injector

Answer

The platform injector is created by platformBrowserDynamic() and sits above the root injector; it holds platform-wide services shared across multiple Angular apps on the same page.

Question 4

What is the purpose of `@SkipSelf()` in Angular dependency injection?

Accepted Answer

Tells Angular to start the injector lookup from the parent injector, bypassing the current one

Answer

@SkipSelf() causes Angular to skip the current element's injector and search up the tree starting from the parent, preventing circular use of the current injector.

Question 5

How does Angular's `forRoot()` pattern prevent duplicate service instances in feature modules?

Accepted Answer

It provides services in the module's forRoot() call so only the root import registers them

Answer

The forRoot() convention puts service providers in the return value of the static forRoot() method, which is called only once in AppModule, ensuring a single instance.

Angular Web Framework Practice Test

Angular Web Framework Practice Test

Angular Web Framework Services & Dependency Injection 4