viewpost.ts

@Component({
  selector: 'view-post',
  template: `
<comment-list *ngIf="post | async" [postId]="(post | async)?.id"></comment-list>
`
})
export class ViewPost {
  post: Observable<IPost>
  constructor() {
    this.post = this
      .functionThatReturnsAnObservable
      .map(data => data.json());
    )
  }
}