Build Reactive Websites with RxJS

Multicasting with the Subject Class

At its core, a Subject acts much like a regular observable, but each subscription is hooked into the same source, like the publish/share example. Subjects also are observers and have next, error, and done methods to send data to all subscribers at once:

let mySubject = new Subject();

mySubject.subscribe(val => console.log('Subscription 1:', val));
mySubject.subscribe(val => console.log('Subscription 2:', val));

mySubject.next(42);

/*
  Console output:
  Subscription 1: 42
  Subscription 2: 42
*/

Because subjects are observers, they can be passed directly into a subscribe call, and all the events from the original observable will be sent through the subject to its subscribers. ...