Mastering TypeScript 3 - Third Edition

Using Observables

Angular's HttpClient class uses Observables as the mechanism to handle asynchronous calls to REST endpoints. Observables are an implementation of the Observable design pattern, and are provided by the JavaScript library named Reactive Extensions for JavaScript, or simply RxJS. The Observable design pattern uses two concepts named registration and notification. An object that is interested in an event will register with an Observable object. When this event occurs, the Observable object will notify all objects that have registered for this event through a notification step. The RxJS library has extended the basic Observable design pattern to allow for a more fine-grained control over when and where these events are raised. ...