translate.get(...).flatMap(...) not working in pending state

[jonaszuberbuehler]

I'm submitting a ... (check one with "x")

[x] bug report => check the FAQ and search github for a similar issue or PR before submitting
[x] support request => check the FAQ and search github for a similar issue before submitting
[ ] feature request

Not sure if it's a bug or misuse by me...

Current behavior
Using translate.get('...').flatMap(...).subscribe(observer) does not work if this.pending is set.

Expected/desired behavior
The observer gets called with the translation.

Reproduction of the problem
Made a small plunker. Calling doIt() from ngOnInit() does not work, calling it afterwards works just fine. Although I didn't dig too deep it looks like to be caused by this.pending.

[SamVerschueren]

I can confirm this seems like a bug. Have to dive deeper to find the cause.

[imgx64]

I submitted a PR to fix this issue. I used mergeMap instead of Observable.create and it worked. I'm not sure why, but the Observable.create closure was being called with a stopped observer.

[imgx64]

Ok, I found the root issue. getTranslation was using share() which was creating a hot observable, and then immediately subscribing to it. Once this subscription was done, the pending observable stopped because there are no more subscribers. Any subscribers afterwards were ignored.

[ocombe]

There's a good reason for adding the share, otherwise it will request multiple times the json file from the server (or anything else that a custom loader can do) if you have multiple translations on your page. Imagine a page with 10 translated words, then it would make 10 http requests.
I'll take a look at the problem but removing share is not an option.

[imgx64]

TranslateService.getTranslation gets called only once the first time a language is used (or if you explicitly call it or call reloadLang). It doesn't get called for every translated word.

But even if getTranslation is called multiple times, it would still do multiple HTTP requests even with the share, because it's creating a new observable every time it's called, not reusing the shared observable.

I don't think share is what you want. share uses refCount, so once all subscriptions are done, the shared observable unsubscribes from the original (http) observable and stops emitting. Any observers that subscribe afterwards simply never get called (neither onNext nor onComplete).

[imgx64]

Okay. I found the root root root issue!

It's a bug in RxJS (ReactiveX/rxjs#2145) that affects hot observables. I've added a PR that fixes this bug without removing the share().

[ocombe]

Thanks a lot for taking the time to find another solution and submitting a PR, I've merged it!