fromStore() wrapper not updating deep reactivity - both ways

[dualjack]

Describe the bug

When using fromStore()

<script lang=ts>
	import {writable, fromStore} from "svelte/store";
	
	const x = writable({name: 'test'});
	const y = fromStore(x);
</script>

updating deep value of y.current.name - is not triggering update of x.name.
See below for playground link.

---

Additional info:
Using primitive value for store, ex.

conxt x = writable('TEXT')
const y = fromStore(x);

y.current = 'blabla';

works fine.

Reproduction

https://svelte.dev/playground/9c230404f43548bd9098c598ff205285?version=5.33.8

Logs

System Info

Svelte 5.33.X

Severity

blocking an upgrade

[Ocean-OS]

fromStore doesn't proxy the store, so you don't get deep reactivity.

[dualjack]

fromStore doesn't proxy the store, so you don't get deep reactivity.

Thank you for your response!

Could you kindly show me where is it documented?
I must have missed something in docs.

What is the point of having fromStore() if it literally converts one format to other - just in time. Seems redundant and misleading in context of stores and reactivity.

[dummdidumm]

It is not documented because why would we document the non-existence of something (exceptions apply ofc)?

These helpers are meant as helping convert one to the other while the source is the, well, source of truth, so you should update only the source and not the derivation.

Therefore closing, but feel free to clarify what in the documentation would have helped you to not get confused, maybe we can add something