title: For the Angular router events Observable, why is there no unsubscribe()?
body: <p>In my <strong>ngOnInit</strong> method I am subscribing to the Router like this:</p>
  
  <pre><code>this.router.events.subscribe(
    event =&gt; {
      if (event instanceof NavigationEnd) this.clearMessages();
    }
  );
  </code></pre>
  
  <p>Normally, for <strong>Observables</strong> outside of the <strong>HttpClient</strong> package I call <strong>unsubscribe</strong> in the <strong>ngOnDestroy</strong> method but when I tried that here I discovered that <strong>this.router.events</strong> does not have such a method.  Am I mistaken or is there something different about this <strong>Observable</strong>?  Why would <strong>unsubscribe</strong> not be implemented?</p>