title: Angular/Rxjs run store (ngrx) calls synchronously
body: <p>I need to perform an action, after retrieving 2 objects from my store (ngrx), so, I need both calls to have responded before performing my action, like this :</p>
  <pre><code>const item1$: Observable&lt;Item&gt; = this._store$.select(
    ItemStoreSelectors.selectItemById(this.id1)
  );
  
  const item2$: Observable&lt;Item&gt; = this._store$.select(
    ItemStoreSelectors.selectItemById(this.id2)
  );
  
  let item1: Item;
  item1$.pipe(take(1)).subscribe((item: Item) =&gt; {
    item1 = item;
  });
  
  let item2: Item;
  item2$.pipe(take(1)).subscribe((item: Item) =&gt; {
    item2 = item;
  });
  
  // here, items might not have been initialized
  doSomething(item1, item2);
  </code></pre>
  <p>I tried to look out for a solution in rxjs with switchMap, mergeMap, etc, but couldn't apply it to my needs. I think I found a solution doing async/await, but I'm not sure this is a good practice.</p>
  <p>Thanks for your help.</p>