Science Knowings: JavaScript Course For Social Media

Angular Dependency Injection

Angular Routing: A Quick Recap

In our previous session, we covered Angular Routing, which enables you to manage the navigation and display of different views within your Angular application. Routing allows you to create dynamic, single-page applications with multiple views, providing a seamless user experience.

Introducing Angular Dependency Injection (DI)

Today, we'll dive into Angular Dependency Injection (DI), a powerful mechanism that enables you to manage dependencies and create loosely coupled, maintainable Angular applications.

Benefits of Dependency Injection

Benefits of DI in Angular:

  • Modularity and Testability: DI promotes modularity by allowing you to easily replace or mock dependencies, making testing easier.
  • Extensibility: DI enables you to extend and customize Angular applications by creating your own custom providers.
  • Reduced Coupling: DI helps reduce coupling between components and services, making your code more flexible and maintainable.

Dependency Injection Providers

DI providers are responsible for creating and delivering instances of dependencies to components and services.

Types of DI Providers

Types of DI Providers:

  • Class Provider: The most common provider type, where you specify the class to be instantiated.
  • Factory Provider: Allows you to create dependencies using a factory function.
  • Value Provider: Used to provide a constant value.

Constructor Injection

Constructor injection is the most straightforward way to inject dependencies. You define the dependencies in the constructor of the component or service.

@Injectable()
export class MyComponent {
  constructor(private myService: MyService) {}
}

Method Injection

Method injection allows you to inject dependencies into methods. You use the @Inject() decorator to specify the dependency.

@Injectable()
export class MyComponent {
  @Inject(MyService) private myService: MyService;
  foo() { /* Use this.myService */ }
}

Property Injection

Property injection is similar to constructor injection, but you inject dependencies directly into class properties.

@Injectable()
export class MyComponent {
  @Inject(MyService) public myService: MyService;
}

DI Token

DI tokens are unique identifiers used to identify dependencies. They can be classes, strings, or custom objects.

Custom DI Provider

Custom DI providers allow you to create your own custom logic for dependency creation.

Creating and Using Custom Providers

Creating Custom Providers:

  • Create a provider class that implements the Provider interface.
  • Specify the dependency to be provided and its creation logic in the provide() and useFactory() methods.
Using Custom Providers:
  • Import the custom provider module into your application module.
  • Use the custom provider in your component or service using DI.

Module Injector

The module injector is created for each Angular module. It's responsible for providing dependencies within that module.

Root Injector

The root injector is the top-level injector in an Angular application. It's responsible for providing dependencies across the entire application.

Using DI in Components

Inject dependencies into Angular components by defining them in the constructor or using the @Inject() decorator.

@Component({ /* ... */ })
export class MyComponent {
  constructor(private myService: MyService) {}
}

Using DI in Services

Similar to components, inject dependencies into Angular services by defining them in the constructor or using the @Inject() decorator.

@Injectable()
export class MyService {
  constructor(private myRepo: MyRepo) {}
}

Using DI in Custom Directives

Inject dependencies into custom directives using the @Host() or @Self() decorators in the constructor.

@Directive({ /* ... */ })
export class MyDirective {
  constructor(@Host() private myService: MyService) {}
}

Best Practices for DI

Best Practices for DI:

  • Use DI for all dependencies, not just singletons.
  • Inject dependencies through constructors whenever possible.
  • Avoid using DI for simple values (e.g., strings or numbers).
  • Prefer constructor injection over method injection.
  • Test your DI configuration thoroughly.

Next Topic: Angular Testing

In the next session, we'll delve into Angular Testing, a crucial aspect of Angular development. We'll explore different testing techniques and best practices to ensure the reliability and robustness of your applications.