RXJS while loop for pagination

Question

I try to query all people data from the swap api. The URL swapi.co/api/people returns an object with an people array and the URL(swapi.co/api/people/?page=2) where I get the nex

Answer 1

By using the expand operator you can create a new Observable sequence for each value that is returned. To stop the expand from creating any new sequences, once we get a next URL that is null, we can return an empty Observable to stop expanding our sequences. Finally, we can use a reduce operator to aggregate the different pages of data into one array that we then emit back to the original subscriber. This can be accomplished as follows:

public getAllPeople(): Observable<Person[]> {
    return Observable.create(observer => {
          this.getPage("http://swapi.co/api/people/")
            .expand((data, i) => {
                return data.next ? this.getPage(data.next) : Observable.empty();
            })
            .reduce((acc, data) => {
                return acc.concat(data.results);
              }, [])
            .catch(error => observer.error(error))
            .subscribe((people) => {
                  observer.next(people);
                  observer.complete();
            });
    });
}

private getPage(url: string): Observable<{next: string, results: Person[]}> {
  return this.http.get(url, { headers: this.headers })
            .map(response => {
                    let body = response.json();
                    return {
                      next: body.next,
                      results: body.results as Person[]
                    };
                }
            );
}

Demo

Answer 2

Use expand operator like:

function getData(id) {
   let next = id<5 ? id+1 : null;
   let obj = {id:id, next:next}
   return next ?   Rx.Observable.of(obj) : Rx.Observable.empty();
 }

 getData(0)
   .expand(el=> getData(el.next))
   .subscribe(x=>console.log(x));