How dependency injection works in Angular - Quick Revision & Summary

Recall & Review

beginner

What is Dependency Injection (DI) in Angular?

Dependency Injection in Angular is a design pattern where Angular automatically provides components or services with the dependencies they need, instead of creating them manually.

intermediate

How does Angular know which dependency to inject?

Angular uses tokens, usually class types, to look up and provide the correct dependency from its injector tree.

intermediate

What is an Angular injector?

An injector is a container that holds and manages the creation and lifetime of dependencies. Angular creates a tree of injectors to provide dependencies at different levels.

beginner

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

The @Injectable() decorator marks a class as available to be injected as a dependency and allows Angular to inject other dependencies into it if needed.

beginner

How can you provide a service at the root level in Angular?

You can provide a service at the root level by adding providedIn: 'root' in the @Injectable() decorator, making it a singleton available throughout the app.

What does Angular use to decide which dependency to inject?

A Random selection

B Tokens like class types

C Manual user input

D File names

Angular uses tokens, usually class types, to find and inject the correct dependency.

What decorator marks a class as injectable in Angular?

A @Component

B @Directive

C @Injectable

D @NgModule

The @Injectable decorator tells Angular that the class can be injected as a dependency.

Where is a service provided if you use providedIn: 'root'?

A In the root injector, available app-wide

B Only in the component

C In the module only

D Nowhere, it disables the service

providedIn: 'root' makes the service a singleton available throughout the entire app.

What is the Angular injector responsible for?

A Managing dependencies and their lifetimes

B Handling HTTP requests

C Rendering UI

D Styling components

The injector manages creating and providing dependencies to components and services.

How does Angular provide dependencies to a component?

A By using global variables

B By manually creating them inside the component

C By importing them in the template

D By injecting them through the constructor

Angular injects dependencies by passing them as parameters in the component's constructor.

Explain how Angular's dependency injection system finds and provides a service to a component.

Think about how Angular uses the constructor and injector to supply dependencies.

Describe the purpose of the @Injectable() decorator in Angular dependency injection.

Consider what makes a class ready to be used as a service.