title: RXJS MergeMap not getting executed
body: <p>In the below code, the execution never goes to mergemap. Looking for some help with correcting this code.</p>
  <p>Requirement is, once i get response from getBns method, i need to perform some operation with response and then using the tap operator to update few flags that are used in HTML.</p>
  <p><em><strong>Component.ts</strong></em>*</p>
  <pre><code> this.bns$ = this.myService.getBns().pipe(
            mergeMap((bns) =&gt; {
              performloadKey()
              return bns
            }),
            tap((bns) =&gt; {
              console.log(bns);
            })
          );
  
  
  this.bns$.pipe(takeUntil(this.destroyed$)).subscribe();
  </code></pre>
  <p><strong><strong>service.ts</strong></strong></p>
  <pre><code>getBns(): Observable&lt;any&gt;{
      return of(mockData); 
    }
  </code></pre>