title: how to combine multiple observables on first observable complete and return as new observable in method
body: <p>I am a beginner to use RxJs operators and I am having a requirement of a method, which calls 5 observables from service and it should fetch data from service only after first observable completes,  then combine all the observables and transform to a new observable and return a new observable with in a function. The below code illustrates the scenario. </p>
  
  <pre><code>GetAllDetails(): Observable&lt;AllDetails&gt; {
  
  const user = this.service.getUser() // Observable&lt;User&gt;
  const firstDetails = this.service.getFirstDetail() // returns Observable&lt;FirstDetail&gt;
  const secondDetails = this.service.getSecondDetail() // returns Observable&lt;SecondDetail&gt;
  const thirdDetails = this.service.getThirdDetail() // returns Observable&lt;ThirdDetail&gt;
  const fourthDetails = this.service.getFourthDetail() // returns Observable&lt;FourthDetail&gt;
  
  // need to return a value that something compatible with Observable&lt;AllDetails&gt;
  // so the logic should check if user info available then do combining all observable values and 
  // return as new observable 
  
  return of(new AllDetails(first, second, third, fourth) 
  }
  </code></pre>
  
  <p>I tried using CombineLatest and switchMap, but I cannot achieve this after my first observable complete. Appreciate if someone could help me out on this. </p>