fix: correctly coordinate component-level effects inside async blocks#18260
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While looking at the reproduction in #18221 (comment) I immediately got greeted with a runtime error when running it in the playground (weirdly not in the Stackblitz version). The error was that a component expected a binding to be set in onMount, but the timing of onMount was wrong. Turns out it's because our logic to determine whether or not to defer top level effects is flawed. `REACTION_RAN`, which was used previously, is already set if the initialized component is inside an async block. We instead check for `component_context.i` which is set to `true` on `pop()`.
🦋 Changeset detectedLatest commit: c29eb51 The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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Stackblitz did not throw this error because |
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No worries, this caught another bug so that's good 😄 |
Rich-Harris
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May 21, 2026
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May 27, 2026
This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## svelte@5.55.10 ### Patch Changes - fix: unlink errored and otherwise finished batch ([#18264](#18264)) - perf: walk composedPath() directly in delegated event propagation ([#18268](#18268)) - fix: transfer effects when merging batches ([#18254](#18254)) - fix: allow `$derived(await ...)` in disconnected effect roots ([#18273](#18273)) - fix: remove temporary raw-text hydration markers ([#18269](#18269)) - fix: propagate async `@const` blockers through closure references so template expressions like `{(() => host)()}` correctly wait for the awaited value ([#18309](#18309)) - fix: properly unlink batches ([#18298](#18298)) - fix: settle discarded batch ([#18290](#18290)) - fix: declare `let:` directives before `{@const}` declarations on slotted elements ([#18271](#18271)) - fix: resume outro-ed branches if they were kept around ([#18291](#18291)) - fix: avoid waterfall-warning when async resolves to same value ([#18297](#18297)) - fix: correctly coordinate component-level effects inside async blocks ([#18260](#18260)) - fix: make unnecessary commit work less likely ([#18263](#18263)) - chore: add tag name to `a11y_click_events_have_key_events` warning ([#18272](#18272)) - fix: catch rejected promises while merging/committing ([#18266](#18266)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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While looking at the reproduction in #18221 (comment) I immediately got greeted with a runtime error when running it in the playground (weirdly not in the Stackblitz version). The error was that a component expected a binding to be set in onMount, but the timing of onMount was wrong.
Turns out it's because our logic to determine whether or not to defer top level effects is flawed.
REACTION_RAN, which was used previously, is already set if the initialized component is inside an async block. We instead check forcomponent_context.iwhich is set totrueonpop().