I'm using mongodb, nodejs and angular (v13.3.0) where i have a model with a nested array (array of arrays).

Data is fetched like this ...

export interface Post {
  _id: string;
  topicId: string;
  url: string;
  title: string;
  description: string;
  subject: string;
  type: PostType | string;
  lessonDate: string;
  lastUpdate: string;
  schoolWeek: number;
}

export interface PostMatching extends Post {
  elements: MatchingPair[][];
}

export type PostTypes = PostArticle | PostQuiz | PostMatching | PostIndexCards;

getPost(postUrl: string): Observable<PostTypes> {
    return this.httpClient.get<PostTypes>(`${this.POSTS_ENDPOINT}/url/${postUrl}`).pipe(
      map((response) => {
        // console.log('response GET post', response);
        return response;
      }),
    );
  }

on the nested array i need to do a for each loop but the reference is typeof object so i get the following error ...

const pairs = this.matching.elements[this.round];
pairs .forEach((pair) => {
  ...
});

I already checked the mongodb document, the nested array is indeed an array in the database.

My workaround looks like this ...

// TODO: check why array in array is typeof object
const pairs = Object.values(this.matching.elements[this.round]);

I wonder what is the problem here, i already checked the value with Array.isArray() which is false, also i logged the value in console and it seems the array is actually a object.

Anyone had this problem before? Thanks in advance :)