Perf: shared mutation router for subtree watchers (#150 Tier 2)#155
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Collapse one MutationObserver per `createSubtreeWatcher` into one shared observer per observed root, with per-subscriber fan-out. The 24 rules that all watch `document.body` previously installed 24 observers, 24 visibilitychange listeners, and 24 route-change subscriptions, each running the same nodeType/IGNORE_TAGS/isConnected filter; now they share one of each, with the cheap shared filter running once per added node regardless of subscriber count. Public API (`createSubtreeWatcher` / `SubtreeWatcher`) is unchanged. Per-subscriber `throttleMs`, `skipPlaceholderSubtrees`, and burst-flush behavior stay independent. Last subscriber to stop() tears the router down (disconnect, remove listeners, cancel rAF, delete from registry). Adds `__resetSubtreeWatcherForTesting` mirroring the existing `__resetRouteChangeForTesting` so test isolation does not depend on every `stop()` running. Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
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Summary
createSubtreeWatcherMutationObserverwith one shared observer per observed root that fans out to subscribers (uBO'ssafeObserverHandlermodel — issue Perf: speed up rule application during fast infinite scroll and SPA route transitions #150 Tier 2 idea build(deps): Bump actions/deploy-pages from 4 to 5 #10).document.body, this collapses 24 observer callbacks, 24visibilitychangelisteners, and 24subscribeRouteChangecallbacks into one each; the sharednodeType/IGNORE_TAGS/isConnectedfilter runs once per added node regardless of subscriber count.throttleMs,skipPlaceholderSubtrees, burst-flush,pending) stays independent —createSubtreeWatcher/SubtreeWatcherAPI is unchanged, so no call site updates are needed.Mechanics
Map<Node, Router>keyed by observed root. First subscriber on a target creates the router + observer + listeners; last subscriber tostop()tears it all down and deletes the map entry.Documentanddocument.bodycollapse to the same router viaresolveTarget.document.head(used bymeta-injection-strip) gets its own router.onSubtrees([document.body])— preserves existing sweep semantics.__resetSubtreeWatcherForTestingmirroring__resetRouteChangeForTestingso test isolation doesn't depend on everystop()running.Test plan
bun run test src/lib/__tests__/subtree-watcher.test.ts— 45/45 pass (35 existing + 10 new covering fan-out, single-observer-construction via constructor spy, independentskipPlaceholderSubtrees/throttleMs, partial-stop keeping observer alive, full teardown on last stop,Document↔bodyrouting, body vs. head router isolation, route-change and visibility fan-out).bun run test— 1200/1200 pass across all 63 suites (covers all 24 rule consumers transitively).bun run typecheckclean.bun run check(Biome + ESLint) clean.🤖 Generated with Claude Code