Creating an Observable authentication service using BehaviorSubjects

One of the most obvious and useful cases of the Observer Pattern is the one in which a single entity in your application unidirectionally communicates information to a field of listeners on the outside. These listeners would like to be able to attach and detach freely from the single broadcasting entity. A good initial example of this is the login/logout component.

Note

The code, links, and a live example of this are available at http://ngcookbook.herokuapp.com/6957/.

Getting ready

Suppose you have the following skeleton application:

[app/login.component.ts] 
 
import {Component} from '@angular/core'; 
 
@Component({ 
  selector: 'login', 
  template: ` 
    <button *ngIf="!loggedIn"  
            (click)="loggedIn=true"> 
      Login 
    </button> 
    <button *ngIf="loggedIn"  
            (click)="loggedIn=false"> 
      Logout 
    ...