Bug: Unsubscribe not called for synced observable

[kruczy]

Hi 👋

I am trying to integrate 3rd party subscription into legend observable, I need to know when the data is observed to make sure I can manage the other subscription accordingly, tho I saw unsubscribe is never called for my case.

Below is a simple repro unsubscribe log is never called (running 3.0.0-beta.17):

const syncedObservable = observable(
	synced({
		get: () => 'foo',
		subscribe: () => {
			console.log('subscribe');

			return () => console.log('unsubscribe');
		},
	})
);

const Observer = observer(() => {
	return <Text>{syncedObservable.get()}</Text>;
});

const Root = () => {
	const [show, setShow] = useState(false);

	useEffect(() => {
		const interval = setInterval(() => setShow((show) => !show), 2000);

		return () => clearInterval(interval);
	}, []);

	return show ? <Observer /> : null;
};

Unsubscribe is called if I use useObservable(synced directly, tho it does not really satisfy my case.

Thanks
Great lib btw 🔥

[jmeistrich]

Ah interesting! It's supposed to unsubscribe when no longer observed. So I'll look into that. I have a feeling it may be caused by strict mode. I'll let you know.

[kruczy]

Hey :)
Thanks for looking into it, I am actually not using strict mode if that helps with debugging. Ill try to create an example outside of react if that is possible 🤔

[kruczy]

ok here is an out of react example:

const syncedObservable = observable(
	synced({
		get: () => 'foo',
		subscribe: () => {
			console.log('subscribe');

			return () => console.log('unsubscribe');
		},
	})
);

const unsubscribe = observe(() => {
	console.log(syncedObservable.get());
});

setTimeout(unsubscribe, 500);

[jmeistrich]

Hmm, I think maybe the issue is that stopping observing does not (currently) immediately call the unsubscribe function. On the next update it will see that it's not currently being observed and then call unsubscribe. So I think if you set it to something after unsubscribing you'll see that "unsubscribe" log.

But I can see how that's not the ideal behavior! I'll see if I can improve that.

[kruczy]

That does not appear to make a difference unless I understood it wrong but I tried 2 things:

• call the update function that is passed in subscribe call
• calling syncedObservable.set(..)

in both cases value updates while subscribed correctly but if called after unsubscription happened does not call the unsubscription callback

[jmeistrich]

Ok, I'll look into it more and get back to you.