title: Wait for an API call to complete without using toPromise() rxjs operator
body: <p>There are several APIs that I am consuming in my application. Although some API calls are interrelated. I want to make sure that the previous API call is completed. I am using the <code>.toPromise()</code> method to handle the scenario currently.</p>
  <p>What other alternatives do you suggest <strong>besides converting an Observable to a Promise?</strong></p>