Angular - Correctly using RXJS expand operator to make recursive http calls

Question

I am attempting to make recursive http calls to Reddit\'s API using a value from the previous call. The problem is that the previous call is not finished before the next one

Answer 1

Returning the same function getSavedPostsForAuthenticatedUser will cause recursive expands. To solve this you need to separate the http observable.

  private getSavedPostsForAuthenticatedUser(username: string, after: string, userPosts: any) {
    const request$ = this._getRequest(username, after, userPosts);
    if (!userPosts) {
      userPosts = [];
    }
    return request$
      .expand(response => {
        if (response.data) {
          for (const post of response.data.children) {
            userPosts.push(post);
          }
          if (response.data.after) {
            return this._getRequest(username, response.data.after, userPosts);
          }
        }
        return Observable.of(userPosts);
      });
  }

  private _getRequest(username: string, after: string) {
    const headers = new Headers();
    headers.append('Authorization', `Bearer ${this._token}`);
    const redditUrl = `${RetainerConfig.redditOauthUrl}user/${username}/saved`;
    const url = after ? `${redditUrl}/?after=${after}` : redditUrl;

    return this._http.get(url, {headers: headers})
      .map(response => response.json());
  }

To stop the expanding you may use Observable.empty(). Please refer to this post.