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fix: assign variables as late as possible

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shirakaba
2022-12-21 16:25:24 +09:00
parent 569b1f2de3
commit decccabd9e
1 changed files with 13 additions and 11 deletions
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24
packages/core/data/dom-events/dom-event.ts
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@@ -121,7 +121,7 @@ export class DOMEvent implements Event {
// Strictly speaking, we should use { public get, private set } for all of // Strictly speaking, we should use { public get, private set } for all of
// `eventPhase`, `currentTarget`, and `target`, but using simple properties // `eventPhase`, `currentTarget`, and `target`, but using simple properties
// saves 800 nanoseconds per run of handleEvent() (and so is one of our // saves 800 nanoseconds per run of dispatchTo() (and so is one of our
// biggest optimisations). // biggest optimisations).
/** /**
@@ -393,14 +393,6 @@ export class DOMEvent implements Event {
for (let i = this.listenersLazyCopy.length - 1; i >= 0; i--) { for (let i = this.listenersLazyCopy.length - 1; i >= 0; i--) {
const listener = this.listenersLazyCopy[i]; const listener = this.listenersLazyCopy[i];
// 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 event listener may have been removed since we took a copy of
// the array, so bail out if so. // the array, so bail out if so.
// //
@@ -418,6 +410,10 @@ export class DOMEvent implements Event {
continue; continue;
} }
// Assigning variables this old-fashioned way is up to 50
// nanoseconds faster per run than ESM destructuring syntax.
const capture = listener.capture;
// Handle only the events appropriate to the phase. Global events // Handle only the events appropriate to the phase. Global events
// (a NativeScript-only concept) are allowed to be handled // (a NativeScript-only concept) are allowed to be handled
// regardless of phase, for backwards-compatibility. // regardless of phase, for backwards-compatibility.
@@ -425,7 +421,10 @@ export class DOMEvent implements Event {
continue; continue;
} }
if (once) { const callback = listener.callback;
const thisArg = listener.thisArg;
if (listener.once) {
// Calling with the context (rather than eagerly pre-binding it) // Calling with the context (rather than eagerly pre-binding it)
// saves about 100 nanoseconds per dispatchTo() call. // saves about 100 nanoseconds per dispatchTo() call.
removeEventListener.call(removeEventListenerContext, this.type, callback, thisArg, capture); removeEventListener.call(removeEventListenerContext, this.type, callback, thisArg, capture);
@@ -441,11 +440,14 @@ export class DOMEvent implements Event {
// This ensures that errors thrown inside asynchronous functions do // This ensures that errors thrown inside asynchronous functions do
// not get swallowed. // not get swallowed.
//
// This check costs only 25 nanoseconds per dispatchTo(), so is not
// a huge deal.
if (returnValue instanceof Promise) { if (returnValue instanceof Promise) {
returnValue.catch(console.error); returnValue.catch(console.error);
} }
if (passive && this.defaultPrevented) { if (listener.passive && this.defaultPrevented) {
console.warn('Unexpected call to event.preventDefault() in passive event listener.'); console.warn('Unexpected call to event.preventDefault() in passive event listener.');
} }