title: Chain multiple RxJS observables and assign value
body: <p>I have properties</p>
  <pre><code>currentApplication: IApplicationModel;
  logos: IImagesModel[];
  backgrounds: IImagesModel[];
  </code></pre>
  <p>And I have three observables like this:</p>
  <pre><code>  loadApplication(): Observable&lt;IApplicationModel&gt; {
      return this.applicationService.getById(this.applicationId);
    }
    loadApplicationLogos(): Observable&lt;IImagesModel[]&gt; {
      return this.applicationService.getApplicationFiles(this.applicationId, &quot;logo&quot;);
    }
    loadApplicationOldBackgrounds(): Observable&lt;IImagesModel[]&gt; {
      return this.applicationService.getApplicationFiles(this.applicationId, &quot;background&quot;);
    }
  </code></pre>
  <p>and they do not depend on each other. I want to have ONE subscription, for example with mergeMap(), but I want also to assign the result of each observable.</p>
  <pre><code>this.loadApplication()
        .pipe(
          mergeMap(application =&gt; this.loadApplicationLogos()),
          mergeMap(application =&gt; this.loadApplicationOldBackgrounds()),
          
        )
        .subscribe(res =&gt; {
          
        })
  </code></pre>
  <p>How I can assign applications and logos to currentApplication and logos ? Should I use tap() before every mergeMap() or is there a better way with something different from mergeMap?</p>