What is Async Pipe?

Async Pipe is an impure pipe which helps to make it easier to work with Observables. The Async Pipe subscribes to an Observable or Promise and returns the latest value it has emitted. When a new value is emitted, the async pipe marks the component to be checked for changes. When the component gets destroyed, the async pipe unsubscribes automatically to avoid potential memory leaks.

For promises, it automatically calls the "then" method.
For observables, it automatically calls subscribe and unsubscribe.

To use the Async Pipe to handle observables in Angular template we use | async followed by the observable, this will automatically subscribe to the observable and refreshes the component whenever a new value is emitted from the observable.

AsyncPipe uses the OnPush change detection out of the box. We need to make sure that all our business logic is immutable and always returns new objects.