SvelteDate no-update

[dangelomedinag]

Describe the bug

SvelteDate does not work as expected, the date is updated but does not trigger changes to the year in the template

Reproduction

Click on next/previous month until you reach a year before or after. The year value is not updated.

PS: if you uncomment the $inpect() the value updates correctly.

playground

Logs

No response

System Info

version=5.4.0

Severity

blocking an upgrade

[brunnerh]

The value appears to get stuck.

If you switch continuously between December and January, it will update but if you go forward or backward multiple times, so the year does not change between updates at least once, it will be 2024/2025 from then on 🤔

[leonidaz]

getYear() which is deprecated works.

as a workaround for now the following will work:

let year = $derived.by(() => {currentDate.getYear(); return currentDate.getFullYear()});

Playground: getYear() workaround

[leonidaz]

passing a parameter also works, something about memoizing using a derived vs raw Date method in SvelteDate source code:

let year = $derived(currentDate.getFullYear(''));

[Rich-Harris]

whittled the repro down to this

[trueadm]

This is because we are caching the method as a derived, but that derived is constantly getting destroyed because it's created inside a reactive context that re-runs each time. The logic seems to create a new one when it's destroyed but that's problematic and not really the correct fix – if the derived is read in one derived and then destroyed and re-created in another, then the old signal relationship will go stale.

I put up #14512 to fix this and will finish it off tomorrow.

[paoloricciuti]

This is because we are caching the method as a derived, but that derived is constantly getting destroyed because it's created inside a reactive context that re-runs each time. The logic seems to create a new one when it's destroyed but that's problematic and not really the correct fix – if the derived is read in one derived and then destroyed and re-created in another, then the old signal relationship will go stale.

I put up #14512 to fix this and will finish it off tomorrow.

Does this means that every derived from SvelteDate is unowned? Could we check if the current reaction is a derived before creating the svelte date derived and only create the derived without a reactive context if that's the case?

Maybe i'm blabblering 😄

[trueadm]

@paoloricciuti The current reaction might also be an effect and the same issue would be evident. Ideally we'd associate the owner to be that of where the SvelteDate object is created.

[paoloricciuti]

@paoloricciuti The current reaction might also be an effect and the same issue would be evident. Ideally we'd associate the owner to be that of where the SvelteDate object is created.

Uhhh i thought this was only a problem with deriveds but you are right...i guess we could save the current reaction in the constructor tho. I'm trying to think if that could have some edge case (like creating a new Date in the template eg)

[trueadm]

Come to think of it though, we can actually associate it with the nearest parent effect – like we do in props.js logic. That's because we never attach the derived to the effect if it's in a tracking effect, and if it's in a non-tracking effect then it can't run again anyway. I'll make that change tomorrow.

[paoloricciuti]

Closed by #14525