Rx.Observable.from does not properly handle NodeList

[Dorus]

Consider the following code:

const buttons = document.querySelectorAll('.btn');

const button$ = Rx.Observable.from(buttons);
const button2$ = Rx.Observable.from(buttons);

button$.subscribe(x => console.log('observer 1 ', x)); // emit
button$.subscribe(x => console.log('observer 2 ', x)); // nothing
button2$.subscribe(x => console.log('observer 3 ', x)); // emit

Rx.Observable.from should result in a cold observable that emit the same list each time it is subscribed. However, in this example the source is a NodeList and the second subscription does not emit.

[kwonoj]

does fromObservable suppose to return cold explicitly? I thought it depends on source type, like from(Promise) you won't get cold suscribes into new promise each time automatically.

[Dorus]

As far as i know promises are eager so it's not even possible for from(Promise) to be anything other than cold. Only fromPromise(() => Promise) is able to rerun the Promise.

[david-driscoll]

Makes me think that for NodeList (and friends) if it finds the Iterator it's pulling that out. Not 100% sure on that however.

[kwonoj]

I think my main question in here is this: does from explicitly intended to return cold? I think I didn't have indication around those. Dealing with NodeList from static creation seems separate discussion.

[Dorus]

Interesting enough, from does reread the source. I stand corrected:

var ar = [1,2,3];
const ar$ = Rx.Observable.from(ar);
ar$.subscribe(x => console.log('observer 1 ', x)); // 1,2,3

ar[2] = 5
ar$.subscribe(x => console.log('observer 2 ', x)); // 1,2,5

[cartant]

Regarding the iterator, in stable, it's obtained in the constructor. However, in master, it's obtained in _subscribe. So the next major version will behave as the OP is expecting.

[kwonoj]

I just came to remind this, is this related with #2497 ?

[kwonoj]

oh @cartant already pointed it.

[Dorus]

I think i actually prefer from to reread the source, that's quite neat. So all we have to do is wait for the next major.

My question is answered so it can be closed for me, unless anyone has another reason to keep it open?

[kwonoj]

@Dorus let me close issue, and sorry for bringing confusion. I did misread original issue obviously and caused confusions around.

[cartant]

@Dorus You most likely already know this, but you can work around the problem in version 5 using defer:

const button$ = Rx.Observable.defer(() => Rx.Observable.from(buttons));

[Dorus]

@cartant Yes i did know that, but thanks for the suggestion anyway. It's exactly what i suggested @mocheng on gitter 3 november 2017 12:14 as he's the one that came up with this scenario.

@kwonoj No prob about the confusion, at least it kept the issue active and quickly resolved :)

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.