title: RXJS forkJoin also takes Observable<[]>?
body: <p>I have an array of numbers which I transform each number to an observable (which emits at random time) </p>
  
  <p>When all observable are resolved , I display the result.</p>
  
  <p>It's like <code>promise.all</code> so I'm using <code>forkJoin</code>.</p>
  
  <pre><code>let arr: Array&lt;Number&gt; = [1, 2, 3, 4, 5];
  let d = from(arr).pipe(mergeMap(f =&gt; myPromise(f)), toArray());
  const example = forkJoin(d);
  const subscribe = example.subscribe(val =&gt; console.log(val));
  </code></pre>
  
  <p>This does work as expected and I do see the overall results after random (max) time.</p>
  
  <p>However , re-reading the docs , this ^ should not have worked.</p>
  
  <p><a href="https://i.stack.imgur.com/u5QHI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/u5QHI.png" alt="enter image description here"></a></p>
  
  <p>Notice that <code>d</code> is type <code>Observable &lt;{}[]&gt;</code> so it's an Observable of array.</p>
  
  <p><a href="http://reactivex.io/rxjs/class/es6/Observable.js~Observable.html#static-method-forkJoin" rel="nofollow noreferrer"><em>However the docs says</em></a> : </p>
  
  <blockquote>
    <p>sources   :SubscribableOrPromise        Any number of Observables provided
    <strong>either as an array or as an arguments passed directly to the operator</strong>.</p>
  </blockquote>
  
  <p>But here  I don't pass an array. ( meaning , this : <code>forkJoin(...d)</code>  won't work).</p>
  
  <p><strong>Question:</strong></p>
  
  <p>Am I using the forkJoin incorrectly ? and how is it settled with the docs ? </p>
  
  <p><a href="https://stackblitz.com/edit/typescript-evaa9e?file=index.ts" rel="nofollow noreferrer"><strong>OnlineDemo</strong></a></p>