RxJS-forkJoin什么时候触发？

Question

What would cause individual subscribe to trigger, but forkJoin to not trigger?

I've sent off a request which triggers subject.subscribe , but when I've added it to an array to use with forkJoin, the forkJoin().subscribe doesn't run. The result that comes back is an object.

    let responses$ = [];
    _.map(items, (item) => {
        let subject = new Subject();
        this.apiService.postRequest("/api/my-endpoint", data).subscribe(subject);
        responses$.push(subject);
        subject.subscribe((res) => { console.log("this triggers") });
    });

    Observable.forkJoin(responses$).subscribe((res) => {
        console.log("this does not trigger");
    });

And here is postRequest - I'm not sure I'm doing it right, I wanted to chain it like promises.

public postRequest(url: string, data: any) {
    return this.getToken().flatMap((accessToken: Response) => {
        return this.post(url, data, {'Authorization': 'Bearer ' + accessToken});
        });
}

Frankly I just wanted to do something similar to $q.all with promises.

Answer 1

forkJoin will emit an array containing the last values from each of the observables passed to it. It emits the array when all of the observables have completed.

So each observable passed to it will need to emit at least one value and will also need to complete.

The reason your subscription to the joined observable does not trigger is most likely because the observables are not completing. You've not included the implementation of getToken() in the question, but unless that observable completes, forkJoin will neither emit a value nor complete.

You could ensure that the observables complete by using first() in the postRequest implementation:

public postRequest(url: string, data: any) {
  return this.getToken()
    .first()
    .flatMap((accessToken: Response) => {
      return this.post(url, data, {'Authorization': 'Bearer ' + accessToken});
    });
}