Reverse An Observable Array In Angularfire2 Angular 6

I am using a Observable array for real time data coming. The data comes in ascending order, but I need it to display in reverse order. Examples on internet are before angular 5 and the syntax no longer works. Please advise

html

  <tr *ngFor="let card of cards  | async;let last = last ">
              <td> <img [src]="card.frontImageUrl" width=200 height="100"></td>
</td>


refreshCards(){
    this.cards = this.dataSvc.fetchCards().pipe(
      map((cards: any) => cards.map(cardObj => new Card(cardObj.key, cardObj._frontImageUrl, cardObj._backImageUrl, cardObj._status, cardObj._date, cardObj._userId, cardObj._message)))
    );
  }

call to firedb

fetchCards(){
    this.cardList = this.db.list<Card>('adminCardQueue', ref => ref.orderByChild('_date').limitToLast(50))

    return this.cardList.snapshotChanges().pipe(
       map(changes => 
        changes.map(c => ({ key: c.payload.key, ...c.payload.val()}))
       )
      ) ;
  }

You can reverse the array at *ngFor using .slice().reverse()

<tr *ngFor="let card of (cards | async)?.slice().reverse();let last = last ">

The .slice() creates a copy of the array and the .reverse() does the reverse action on your array.