多次订阅可观察的 rxjs

Question

I'm trying to achieve the following:

I have an Observable that can be subscribed to multiple times, although I only want to do some processing once.

export class DataLoader
{
    private loaded = false;
    private data: Data;
    private observable = null;

    load(): Observable<Data> {
        if(this.loaded) {
            console.log('Already loaded');
            return Observable.create((obs) => {
                obs.next(this.data);
                obs.complete();
            })
        }

        if(this.observable === null) {
            console.log('Creating observable');
            this.observable = Observable.create((obs) => {

                console.log('firing xhr');
                let xhr;

                xhr.onload = () => {
                    this.data = data;
                    this.loaded = true;
                    obs.next(data);
                    obs.complete();
                    this.observable = null;
                }

                xhr.onerror = () => {
                    obs.error(error);
                    this.observable = null;
                }
            });
        }

        return this.observable;
    }
}

Lets say I use this DataLoader in 2 different places, the 'xhr' will only be done once.

...
Dataloader.load().subscribe();
...
#At another point in the code
Dataloader.load().subscribe();
...

Console:

Creating observable
firing xhr
Already Loaded

This works correctly as long as the requests aren't fired off too quickly after each other.

To demonstrate, lets put this in a for loop:

for(let i = 0; i<10; i++) {
    DataLoader.load().subscribe();
}

In this case the console looks like this:

Creating observable
firing xhr
firing xhr
firing xhr
firing xhr
firing xhr
firing xhr
firing xhr
firing xhr
firing xhr
firing xhr

How could I manage to use this in a for loop ? I've been looking into a Subject / BehaviourSubject but I cannot seem to make it work.

Cookies for thoughs

Answer 1

I Solved it using the following:

if(this.observable === null) {
    console.log('Creating observable');
    let source = Observable.create((obs) => {

        console.log('firing xhr');
        let xhr;

        xhr.onload = () => {
            this.data = data;
            this.loaded = true;
            obs.next(data);
            obs.complete();
            this.observable = null;
        }

        xhr.onerror = () => {
            obs.error(error);
            this.observable = null;
        }
    });

    let subject = new Subject();

    this.observable = source.multicast(subject);

    this.observable.connect();
}

http://reactivex.io/rxjs/manual/overview.html#multicasted-observables

Answer 2

I opted for using simple promises since all I needed was a multicast event, but it seems rxjs deals with it already with "Subjects"

  return this.service.add(this.formModel.value, this.imageFile)
    .toPromise() // this.subscribe((x) => value = x, (err) => reject(err), () => resolve(value));
    .then(id => this.formVm.editMode(id));