Firestore - get key

// template
<li class="text" *ngFor="let item of items | async">
      {{item.title}} -- {{ item.key}}
</li>

// typescript
this.items = this.itemsCollection.snapshotChanges()
      .map(actions => {
        return actions.map(action => ({ $key: action.payload.doc.id, ...action.payload.doc.data() }));
      });