Svelte 5: compiler may falsy consider variable as non-reactive

[7nik]

Describe the bug

The compiler may consider the variable non-reactive if no explicit calls of methods. However, an object may have a custom stringification method that reads a signal. Such methods are toString, toJSON, valueOf, and Symbol.toPrimitive.

Reproduction

REPL

Logs

No response

System Info

REL Svelte v5.0.0-next.22

Severity

annoyance

[Conduitry]

This one feels like a won't-fix (or maybe even a working-as-designed) to me. If supporting this requires any additional runtime code for people not using a custom toString(), I don't think we should support it.

[7nik]

The original case is more tricky, but I kinda agree.

[7nik]

What about this case with a Date? I suppose date isn't reactive because it is a Date class instance, but shouldn't date = date trigger reactivity? How can I trigger reactivity here without creating a new object?
Though, probably it is another issue.

[trueadm]

@7nik That's because Svelte doesn't treat Date as reactive, so changing its internals will do nothing. You need to re-assign date to a new Date object each time if you want it to be reactive, there's no other way. However, you can rewrite your example so it's a lot cleaner:

[trueadm]

Closing this as I think this isn't something we need to fix.