RxJS append observable to observable array list in

Question

How to add Observable<News> to an array of observable ?

newsArray: Observable<Array<any>>;

addNews(newsId: number) {
   let news = this.newsService.getNewNews(newsId); // this returns a Observable<News> type.

  //I want to add `news` to `newsArray` to display it in UI.
}

HTML:

<li *ngFor="let item of (newsArray | async)">
  <div>{{item.Id}}: {{item.DataValue}}</div>
</li>

Any other operators to use?

I tried BehaviourSubject but it displays only one value at a time. I want to display add items that I am appending to an arrray.

Answer 1

You can use scan to accumulate news

news$:Observable<any>
loadMore$=new Subject<number>()

ngOnInit(){
 this.news$=this.loadMore$
 .switchMap((newsId)=>this.newsService.getNewNews(newsId))
 .scan((acc,curr)=>{
    acc.push(curr)
    return acc
 },[]).startWith(null)
}

addNews(newsId: number) {
  this.loadMore$.next(newsId);
}

HTML

<li *ngFor="let item of (news$ | async)">
  <div>{{item.Id}}: {{item.DataValue}}</div>
</li>