Event system (data/observable)

• notify() now skips the deprecated static/global event-handler machinery entirely (including the this.constructor.name resolution and 4 hash lookups per event) when no global handlers are registered, tracked via a simple module-level counter. Global handler semantics are unchanged when they are used.
• _handleListenerEntry uses callback.call(thisArg, data) instead of callback.apply(thisArg, [data]), removing a throwaway array allocation on every listener invocation.
• hasListeners() uses a direct property read instead of the in operator.
• _indexOfListener uses an indexed loop instead of findIndex + closure (runs on every addEventListener).

Property system (ui/core/properties)

• isResetValue() / isCssWideKeyword() — these run at the top of every property setter. They now bail out with a single typeof check for the overwhelmingly common case of non-string values (numbers, booleans, Colors, objects) instead of comparing against every CSS reset keyword.

CSS selector matching (ui/styling)

• SelectorScope.getSelectorCandidates() replaced an O(n·buckets) reduce+concat (which re-copied the accumulator on every bucket) with a single push-based accumulation. This runs for every view on load and on every class/id change.
• AttributeSelector with ignoreCase normalizes its value once at construction instead of lowercasing (and reassigning) it on every match.
• matchMediaQueryString() caches media-query string splits (they come from parsed stylesheets, so the distinct set is small and stable) and avoids per-call closures.
• SimpleSelectorSequence.match/mayMatch/trackChanges, ComplexSelector.match/trackChanges and Selector.ChildGroup.getMatchingNode use indexed loops instead of every/forEach closures; getMatchingNode also drops the string-keyed method dispatch (sel[funcName]).
• CssState.updateDynamicState / setPropertyValues avoid per-call closure allocations (hoisted kebab-case replacement func, indexed filter loop). These run on every pseudo-class change (every tap).

View base (ui/core/view-base)

• addPseudoClass/deletePseudoClass no longer allocate an aliased-states array on every visual-state transition (every tap toggles :highlighted/:active/:pressed).
• classNameProperty.valueChanged uses indexed loops instead of forEach closures (hot in list-item recycling).
• Fixed a latent bug in getViewByDomId(): the descendants callback compared view._domId (the root argument) instead of child._domId, so descendant lookups never matched and always walked the entire subtree.

iOS layout (utils/layout-helper)

• toDevicePixels / toDeviceIndependentPixels / getDisplayDensity now cache the screen scale instead of resolving window → screen → scale through the ObjC bridge on every dp/px conversion (these are called several times per view per measure/layout pass). The device main-screen scale never changes at runtime — Screen.mainScreen already relies on the same invariant, and the Android implementation already caches density this way.

Measured results

Micro-benchmarks (vitest bench, committed under packages/core/__tests__/benchmarks/)

Node v25, darwin arm64, same machine/settings for both runs:

Reproduce with: cd packages/core && npx vitest bench --run

Automated iOS test suite (npx nx debug apps-automated ios, iPhone 17 Pro simulator)