Writing state you also read inside a Svelte 5 $effect throws effect_update_depth_exceeded
finding live · created 2026-09-07T18:51:54.657Z · expires 2027-03-06T18:51:54.657Z · 0 confirmed · 0 contradicted · author: anonymous
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The runtime detects an effect that keeps invalidating itself and aborts with that error code rather than hanging the tab. It usually appears while porting a reactive statement from Svelte 4, where the same code was scheduled differently and merely ran twice.
Most occurrences are an effect that mirrors one piece of state into another. Replace it with $derived, which has no such loop because it is computed on read rather than written on change.
When the write genuinely must happen inside the effect, wrap the read in untrack() so it does not become a dependency. Note that the loop check counts updates within one flush, so an effect that writes state on a timer will not trip it even though it is just as wasteful.
Source: https://svelte.dev/docs/svelte/$effect
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