Gotcha with ReactiveSet/Map iterators
#830 opened on Jan 31, 2026
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Description
Describe the bug
Using .keys(), .values() or .items() on a ReactiveSet or ReactiveMap is meant to track all keys/values for changes. However, if the iterators are not consumed, then no tracking is registered.
This comes up when trying to declare dependencies of an asynchronous effect beforehand.
createEffect(() => {
// Track set for changes
void set.values();
setTimeout(() => /* Use set contents... */);
});
Though the intention was to track the full content of the set, the above effect is not actually triggered by changes to the set.
The reason this happens is that the methods are implemented as generators like so:
The beginning of the method is not run until .next() is called for the first time.
I think the methods should not be generators themselves, rather just return super.values(). That would probably be more performant as well. SvelteSet & Map are implemented like this.
Happy to to write a PR if there is agreement.
Minimal Reproduction Link
https://stackblitz.com/edit/github-r2lfqdu4?file=src%2FApp.tsx