perf: walk composedPath() directly in delegated event propagation#18268
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dummdidumm merged 2 commits intoMay 21, 2026
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The propagation walk in `handle_event_propagation` already calls `event.composedPath()` at the start to find the entry index, but then re-derives the same chain step-by-step via `current_target.assignedSlot || current_target.parentNode || .host`. Three property reads per iteration is measurable on the hot event path. Walk the captured `path` array by index instead. composedPath is the spec-compliant snapshot of the dispatch chain — same shadow-DOM and slot crossings as the manual walk, and arguably more correct in the edge case where a handler removes a parent mid-dispatch (the snapshot continues; the manual walk would stop at a null parent). Measured ~+13% in real Chromium on a click through a 30-deep tree with five delegated handlers. All 6006 runtime tests pass. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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thank you! makes the code simpler aswell
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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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Summary
The propagation walk in
handle_event_propagationalready callsevent.composedPath()at the start to find the entry index, but then re-derives the same chain step-by-step viacurrent_target.assignedSlot || current_target.parentNode || .host. Three property reads per iteration is measurable on the hot event path.Walk the captured
patharray by index instead.Notes on behavior
composedPath()is the spec-compliant snapshot of the dispatch chain:hosttraversal (composed-path crosses shadow boundaries when appropriate).parentNodewalk would have stopped at a null parent).Performance
Measured in real Chromium on a click through a 30-deep tree with five delegated handlers: ~245k hz → ~277k hz (~+13%, ~−12% per-event time).
Test plan
🤖 Generated with Claude Code