Dependency injection is a design pattern used in Angular to manage the dependencies between components, services, and other objects in a loosely-coupled manner. It enables you to write code that is more flexible, maintainable, and testable by separating the responsibilities of a component into smaller, reusable services.
Here’s how dependency injection works in Angular:
- Registering the dependencies: The first step is to register the dependencies that a component requires as injectable services. This is done using the
@Injectabledecorator in Angular. - Injecting the dependencies: Once the dependencies are registered, they can be injected into a component using the constructor. Angular uses the metadata provided in the
@Injectabledecorator to determine which services should be injected. - Resolving the dependencies: When a component is created, Angular uses its dependency injector to resolve the dependencies and instantiate the required services. It then passes these services into the component’s constructor, making them available for use throughout the component.
- Managing the dependencies: Angular uses a hierarchical injector system to manage the dependencies between components. This means that a component’s injector can delegate the resolution of its dependencies to its parent injector, making it possible to define a global injector for an entire application.
By using dependency injection, you can ensure that components are loosely-coupled and easy to maintain and test. The dependencies are clearly defined and can be easily swapped out or replaced without affecting the rest of the application.