Angular 7|8 Services

After understanding modules and components, let’s see what services are.

In Angular, a service is a singleton that can be wired with components or other services via Dependency Injection.

According to Wikipedia:

In software engineering, dependency injection is a technique whereby one object supplies the dependencies of another object.

Don’t be intimidated by this term, it simply means that Angular (or a part of Angular, the injector) takes care of instantiating the services and provides the instance to the requesting component.

According to the Angular docs:

DI is wired into the Angular framework and used everywhere to provide new components with the services or other things they need. Components consume services; that is, you can inject a service into a component, giving the component access to that service class.

You can use services to organize and share code across your app

Typically, a component's job is to enable the user experience and nothing more. A component should present properties and methods for data binding, in order to mediate between the view (rendered by the template) and the application logic.

A component can delegate certain tasks to services, such as fetching data from the server, validating user input, or logging directly to the console.

By defining such processing tasks in an injectable service class, you make those tasks available to any component.

To define a class as a service in Angular, use the @[Injectable](https://angular.io/api/core/Injectable)() decorator to provide the metadata that allows Angular to inject it into a component as a dependency.

You need to provide a service before it can be available. This can be done in three ways:

  • Via the service’s metadata passed to the @Injectable() decorator (The service will be available everywhere),
  • Via the providers array, in a specific module (The service is available only to the components and services of the module),
  • Via the providers array in a specific component (The service is available only to the component).

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