title: Async pipe doesn't display updated observable value
body: <p>I'm encountering an issue where an async observable in my view doesn't show the observable's updated values. </p>
  
  <p>As I understood it, you should be able to expose the latest observed value in your view by simply using an async pipe in the template (e.g. <code>&lt;p&gt;Hello, {{ name | async }}&lt;/p&gt;</code>). In this case, though, the new value is being emitted outside Angular's world view which seems to cause Angular to ignore the updated value until something else triggers a view update. </p>
  
  <p>I've also tried subscribing to the observable in my component's constructor and manually exposing the updated values as properties on the component, but that didn't work either.</p>
  
  <p>Here's my minimum repo case.</p>
  
  <pre class="lang-js prettyprint-override"><code>// Copyright 2019 Google LLC.
  // SPDX-License-Identifier: Apache-2.0
  
  import { Component } from '@angular/core';
  import { Observable } from 'rxjs';
  
  @Component({
    selector: 'my-app',
    // Replace with your markup
    template: `
      &lt;pre&gt;{{ pumpObs | async }}&lt;/pre&gt;
      &lt;button (click)="noop"&gt;click me&lt;/button&gt;
    `,
    styles: [ `h2 { font-weight: normal; }`]
  })
  
  export class AppComponent  {
    pumpObs = new Observable(observer =&gt; {
      observer.next("New observable");
  
      // Expose a function to modify the observable's value
      (&lt;any&gt;window).pump = val =&gt; {
        console.log(`pumpObs: ${val}`);
        observer.next(val);
      };
  
      // Noop unsubscribe handler
      return this.noop;
    });
  
    noop = () =&gt; {};
  }
  </code></pre>
  
  <p>You can view a live demo at <a href="https://stackblitz.com/edit/angular-issue-repro2-dmkbhg" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-issue-repro2-dmkbhg</a></p>