11import type { EventData , ListenerEntry , Observable } from '../observable/index' ;
22import type { ViewBase } from '../../ui/core/view-base' ;
33
4+ // This file contains some of Core's hot paths, so attention has been taken to
5+ // optimise it. Where specified, optimisations made have been informed based on
6+ // profiles taken on an Apple M1 Max in a debug build on @nativescript /ios@8.3.3
7+ // on an iOS Simulator.
8+
49const timeOrigin = Date . now ( ) ;
510
611/**
@@ -338,11 +343,21 @@ export class DOMEvent implements Event {
338343 private handleEvent ( { data, isGlobal, getListenersForType, phase, removeEventListener } : { data : EventData ; isGlobal : boolean ; getListenersForType : ( ) => readonly ListenerEntry [ ] ; phase : 0 | 1 | 2 | 3 ; removeEventListener : ( eventName : string , callback ?: any , thisArg ?: any , capture ?: boolean ) => void } ) {
339344 // Work on a copy of the array, as any callback could modify the
340345 // original array during the loop.
341- const listenersForTypeCopy = getListenersForType ( ) . slice ( ) ;
346+ //
347+ // Cloning the array via spread syntax is up to 180 nanoseconds faster
348+ // per run than using Array.prototype.slice().
349+ const listenersForTypeCopy = [ ...getListenersForType ( ) ] ;
342350
343351 for ( let i = listenersForTypeCopy . length - 1 ; i >= 0 ; i -- ) {
344352 const listener = listenersForTypeCopy [ i ] ;
345- const { callback, capture, thisArg, once, passive } = listener ;
353+
354+ // Assigning variables this old-fashioned way is up to 50
355+ // nanoseconds faster per run than ESM destructuring syntax.
356+ const callback = listener . callback ;
357+ const capture = listener . capture ;
358+ const thisArg = listener . thisArg ;
359+ const once = listener . once ;
360+ const passive = listener . once ;
346361
347362 // The event listener may have been removed since we took a copy of
348363 // the array, so bail out if so.
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