title: RxJS catchError and return previous value instead of completing?
body: <p>I have a stream which may or may not error, I would like to catchError in order to return the previous/last value before the error in order to continue the stream and not complete. Something along the lines of this:</p>
  
  <pre><code>inputStream$.pipe(catchError(err =&gt; inputStream$.previousValue)).subscribe(...)
  </code></pre>