title: How to check if a Observable is end?
body: <p>I want check if a observable is end to store in database the final result.</p>
  
  <p><strong>Example:</strong></p>
  
  <pre><code>fn () {
      return new Observable( observer =&gt; {
          observer.next(1);
          observer.next(2);
          observer.next(3);
          observer.complete(4);
      });
  }
  
  fn().subscribe( status =&gt; {
      if (this.isEnd()) { // How to check if end???
          //...
      }
  })
  </code></pre>