Remove `flushSync` from svelte-db to avoid breaking async compiler mode by KyleAMathews · Pull Request #745 · TanStack/db

KyleAMathews · 2025-11-03T01:13:11Z

The flushSync() call inside the onFirstReady callback was breaking Svelte 5's async compiler mode. The async compiler enforces a rule that flushSync cannot be called inside effects, as documented at svelte.dev/e/flush_sync_in_effect.

The fix removes the flushSync call and updates status directly. Svelte's reactivity system handles the update automatically without needing synchronous flushing. This matches the pattern used in Vue's implementation.

Changes:

Removed flushSync() wrapper from onFirstReady callback
Removed unused flushSync import
Updated comment to explain why flushSync cannot be used
All 23 existing tests pass, confirming no regression

This fix is backward compatible:

For users WITHOUT async mode (current default): Works as before
For users WITH async mode: Now works instead of throwing error
Future-proof: async mode will be default in Svelte 6

🎯 Changes

✅ Checklist

I have followed the steps in the Contributing guide.
I have tested this code locally with pnpm test:pr.

🚀 Release Impact

This change affects published code, and I have generated a changeset.
This change is docs/CI/dev-only (no release).

…r mode Fixes#744 The flushSync() call inside the onFirstReady callback was breaking Svelte 5's async compiler mode. The async compiler enforces a rule that flushSync cannot be called inside effects, as documented at svelte.dev/e/flush_sync_in_effect. The fix removes the flushSync call and updates status directly. Svelte's reactivity system handles the update automatically without needing synchronous flushing. This matches the pattern used in Vue's implementation. Changes: - Removed flushSync() wrapper from onFirstReady callback - Removed unused flushSync import - Updated comment to explain why flushSync cannot be used - All 23 existing tests pass, confirming no regression This fix is backward compatible: - For users WITHOUT async mode (current default): Works as before - For users WITH async mode: Now works instead of throwing error - Future-proof: async mode will be default in Svelte 6

changeset-bot · 2025-11-03T01:13:17Z

🦋 Changeset detected

Latest commit: 6282d4e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@tanstack/svelte-db	Patch

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KyleAMathews · 2025-11-03T01:14:17Z

@wobsoriano does this seem reasonable?

pkg-pr-new · 2025-11-03T01:14:45Z

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commit: 6282d4e

github-actions · 2025-11-03T01:15:21Z

Size Change: 0 B

Total Size: 79.1 kB

ℹ️ View Unchanged

Filename	Size
`./packages/db/dist/esm/collection/change-events.js`	1.34 kB
`./packages/db/dist/esm/collection/changes.js`	977 B
`./packages/db/dist/esm/collection/events.js`	388 B
`./packages/db/dist/esm/collection/index.js`	3.12 kB
`./packages/db/dist/esm/collection/indexes.js`	1.1 kB
`./packages/db/dist/esm/collection/lifecycle.js`	1.67 kB
`./packages/db/dist/esm/collection/mutations.js`	2.26 kB
`./packages/db/dist/esm/collection/state.js`	3.43 kB
`./packages/db/dist/esm/collection/subscription.js`	2.42 kB
`./packages/db/dist/esm/collection/sync.js`	2.02 kB
`./packages/db/dist/esm/deferred.js`	207 B
`./packages/db/dist/esm/errors.js`	3.9 kB
`./packages/db/dist/esm/event-emitter.js`	748 B
`./packages/db/dist/esm/index.js`	2.36 kB
`./packages/db/dist/esm/indexes/auto-index.js`	731 B
`./packages/db/dist/esm/indexes/base-index.js`	766 B
`./packages/db/dist/esm/indexes/btree-index.js`	1.87 kB
`./packages/db/dist/esm/indexes/lazy-index.js`	1.1 kB
`./packages/db/dist/esm/indexes/reverse-index.js`	513 B
`./packages/db/dist/esm/local-only.js`	837 B
`./packages/db/dist/esm/local-storage.js`	2.04 kB
`./packages/db/dist/esm/optimistic-action.js`	359 B
`./packages/db/dist/esm/paced-mutations.js`	496 B
`./packages/db/dist/esm/proxy.js`	3.22 kB
`./packages/db/dist/esm/query/builder/functions.js`	606 B
`./packages/db/dist/esm/query/builder/index.js`	3.85 kB
`./packages/db/dist/esm/query/builder/ref-proxy.js`	917 B
`./packages/db/dist/esm/query/compiler/evaluators.js`	1.26 kB
`./packages/db/dist/esm/query/compiler/expressions.js`	674 B
`./packages/db/dist/esm/query/compiler/group-by.js`	1.78 kB
`./packages/db/dist/esm/query/compiler/index.js`	1.95 kB
`./packages/db/dist/esm/query/compiler/joins.js`	2 kB
`./packages/db/dist/esm/query/compiler/order-by.js`	1.17 kB
`./packages/db/dist/esm/query/compiler/select.js`	1.07 kB
`./packages/db/dist/esm/query/ir.js`	673 B
`./packages/db/dist/esm/query/live-query-collection.js`	360 B
`./packages/db/dist/esm/query/live/collection-config-builder.js`	5 kB
`./packages/db/dist/esm/query/live/collection-registry.js`	214 B
`./packages/db/dist/esm/query/live/collection-subscriber.js`	1.77 kB
`./packages/db/dist/esm/query/optimizer.js`	2.6 kB
`./packages/db/dist/esm/scheduler.js`	1.21 kB
`./packages/db/dist/esm/SortedMap.js`	1.18 kB
`./packages/db/dist/esm/strategies/debounceStrategy.js`	237 B
`./packages/db/dist/esm/strategies/queueStrategy.js`	418 B
`./packages/db/dist/esm/strategies/throttleStrategy.js`	236 B
`./packages/db/dist/esm/transactions.js`	2.9 kB
`./packages/db/dist/esm/utils.js`	881 B
`./packages/db/dist/esm/utils/browser-polyfills.js`	304 B
`./packages/db/dist/esm/utils/btree.js`	5.61 kB
`./packages/db/dist/esm/utils/comparison.js`	660 B
`./packages/db/dist/esm/utils/index-optimization.js`	1.49 kB
`./packages/db/dist/esm/utils/type-guards.js`	157 B

_{compressed-size-action::db-package-size}

github-actions · 2025-11-03T01:15:57Z

Size Change: 0 B

Total Size: 3.34 kB

ℹ️ View Unchanged

Filename	Size
`./packages/react-db/dist/esm/index.js`	225 B
`./packages/react-db/dist/esm/useLiveInfiniteQuery.js`	1.17 kB
`./packages/react-db/dist/esm/useLiveQuery.js`	1.11 kB
`./packages/react-db/dist/esm/useLiveSuspenseQuery.js`	431 B
`./packages/react-db/dist/esm/usePacedMutations.js`	401 B

_{compressed-size-action::react-db-package-size}

samwillis

Approving but with the question - do we have a test that validates this statement:

The fix removes the flushSync call and updates status directly. Svelte's reactivity system handles the update automatically without needing synchronous flushing.

Add test to verify that status changes in useLiveQuery properly trigger reactive re-execution in Svelte effects. This validates that accessing query.isReady/isLoading in component templates will automatically re-render when status changes from loading to ready. The test uses $effect() to track execution counts, confirming that Svelte's $state reactivity system works correctly with the status updates that occur via the onFirstReady callback (which doesn't use flushSync in async compiler mode). 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>

KyleAMathews · 2025-11-05T15:48:14Z

Ah good call — just added an actual test.

Regenerate docs after adding reactive status change test. All files now use correct PascalCase naming to match main branch. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>

…ix-bug-011CUk3w5CN4UmLKb7pLVzzT

Update React reference docs to include useLiveSuspenseQuery hook that was added in main. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>

claude added 2 commits November 3, 2025 01:11

chore: Add package-lock.json to .gitignore (project uses pnpm)
d4df327

KyleAMathews requested a review from samwillis November 3, 2025 01:13

chore: Add changeset for Svelte async mode fix
2494fc8

style: Apply prettier formatting to changeset
77b6fd4

KyleAMathews added this to TanStack DB 1.0.0 release Nov 4, 2025

KyleAMathews moved this to Ready for review in TanStack DB 1.0.0 release Nov 4, 2025

samwillis approved these changes Nov 5, 2025
View reviewed changes

KyleAMathews force-pushed the claude/validate-and-fix-bug-011CUk3w5CN4UmLKb7pLVzzT branch from afb711c to 521f838Compare November 5, 2025 16:08

KyleAMathews force-pushed the claude/validate-and-fix-bug-011CUk3w5CN4UmLKb7pLVzzT branch from 521f838 to 36f8e45Compare November 5, 2025 16:11

KyleAMathewsand others added 2 commits November 5, 2025 09:14

Merge remote-tracking branch 'origin/main' into claude/validate-and-f…
a1d3332
…ix-bug-011CUk3w5CN4UmLKb7pLVzzT

docs: Add useLiveSuspenseQuery reference after merge
6282d4e
Update React reference docs to include useLiveSuspenseQuery hook that was added in main. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>

KyleAMathews merged commit 5fe5b6a into mainNov 5, 2025
7 checks passed

KyleAMathews deleted the claude/validate-and-fix-bug-011CUk3w5CN4UmLKb7pLVzzT branch November 5, 2025 16:22

github-actionsBot mentioned this pull request Nov 5, 2025
ci: Version Packages #767
Merged

KyleAMathews moved this from Ready for review to Done in TanStack DB 1.0.0 release Nov 13, 2025

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Remove `flushSync` from svelte-db to avoid breaking async compiler mode - #745

Remove `flushSync` from svelte-db to avoid breaking async compiler mode#745
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