diff --git a/packages/core/data/dom-events/dom-event.ts b/packages/core/data/dom-events/dom-event.ts index 757a96453..977d8a97c 100644 --- a/packages/core/data/dom-events/dom-event.ts +++ b/packages/core/data/dom-events/dom-event.ts @@ -1,6 +1,11 @@ import type { EventData, ListenerEntry, Observable } from '../observable/index'; import type { ViewBase } from '../../ui/core/view-base'; +// This file contains some of Core's hot paths, so attention has been taken to +// optimise it. Where specified, optimisations made have been informed based on +// profiles taken on an Apple M1 Max in a debug build on @nativescript/ios@8.3.3 +// on an iOS Simulator. + const timeOrigin = Date.now(); /** @@ -338,11 +343,21 @@ export class DOMEvent implements Event { 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 }) { // Work on a copy of the array, as any callback could modify the // original array during the loop. - const listenersForTypeCopy = getListenersForType().slice(); + // + // Cloning the array via spread syntax is up to 180 nanoseconds faster + // per run than using Array.prototype.slice(). + const listenersForTypeCopy = [...getListenersForType()]; for (let i = listenersForTypeCopy.length - 1; i >= 0; i--) { const listener = listenersForTypeCopy[i]; - const { callback, capture, thisArg, once, passive } = listener; + + // Assigning variables this old-fashioned way is up to 50 + // nanoseconds faster per run than ESM destructuring syntax. + const callback = listener.callback; + const capture = listener.capture; + const thisArg = listener.thisArg; + const once = listener.once; + const passive = listener.once; // The event listener may have been removed since we took a copy of // the array, so bail out if so.