Wondering if we should use duck-typing here like https://github.com/denoland/fresh/blob/e65643c482de9b5afee5d52af3ccc88941c35b5c/src/runtime/server/preact_hooks.tsx#L355-L362 . That way we can keep rts dependency free and don't have to keep it in sync with major @preact/signals version increases.

This might end up being a much larger perf hit in the critical path though

Not sure if x !== null && typeof x === "object" is more or less expensive than an instanceof check. I let you decide on that one.

I'd rather avoid adding a dep for a singular instanceof check myself, and at least as of a few years ago, duck-typing with 1-2 properties usually outperformed instanceof in Chrome. No idea of what fully happens internally there, but naively, makes sense to me.

If you've measured it & it is a perf issue, fair enough of course. I'll have some time in a bit to check the benches (if you haven't already).

Edit: At least on my system, the check Marvin linked to above doesn't seem to perform any worse than instanceof. Ran the benches a few times and there wasn't any noticeable drop.