A Singleton Serviceis one which has only one instance shared across the entire Angular App, it is a great way to share data across different components even if they don’t have any Hierarchal relationship. Services can be declared Singleton by setting the providedIn property of the @Injectable() to "root", when creating the service.
@Injectable({
providedIn: 'root',
})
@Injectable({
providedIn: 'root',
})