title: A forkJoin alternative for uncompleted observables?
body: <pre><code>constructor(
      private route: ActivatedRoute,
      private http: Http
  ){
      // Observe parameter changes
      let paramObs = route.paramMap;
  
      // Fetch data once
      let dataObs = http.get('...');
  
      // Subscribe to both observables,
      // use both resolved values at the same level
  }
  </code></pre>
  
  <p>Is there something similar to <code>forkJoin</code> that triggers whenever a parameter change is emitted? <code>forkJoin</code> only works when all observables have completed.</p>
  
  <p>I just need to avoid callback hell, any alternative that complies is welcome.</p>