@lightningjs/renderer
Version:
Lightning 3 Renderer
136 lines • 4.7 kB
JavaScript
/*
* If not stated otherwise in this file or this component's LICENSE file the
* following copyright and licenses apply:
*
* Copyright 2023 Comcast Cable Communications Management, LLC.
*
* Licensed under the Apache License, Version 2.0 (the License);
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* EventEmitter base class
*
* @remarks
* The `eventListeners` map is allocated lazily on the first `on()` call.
* Many objects (e.g. CoreNodes that never have listeners attached) avoid
* the cost of allocating an empty `{}` at construction time.
*/
export class EventEmitter {
eventListeners = null;
on(event, listener) {
let map = this.eventListeners;
if (map === null) {
map = {};
this.eventListeners = map;
}
let listeners = map[event];
if (listeners === undefined) {
listeners = [];
map[event] = listeners;
}
listeners.push(listener);
}
off(event, listener) {
const map = this.eventListeners;
if (map === null) {
return;
}
const listeners = map[event];
if (listeners === undefined) {
return;
}
if (listener === undefined) {
// Set to undefined instead of `delete` to avoid V8 hidden-class
// transitions on the eventListeners object.
map[event] = undefined;
return;
}
const index = listeners.indexOf(listener);
if (index >= 0) {
listeners.splice(index, 1);
}
}
once(event, listener) {
const onceListener = (target, data) => {
this.off(event, onceListener);
listener(target, data);
};
this.on(event, onceListener);
}
emit(event, data) {
const map = this.eventListeners;
if (map === null) {
return;
}
const listeners = map[event];
if (listeners === undefined || listeners.length === 0) {
return;
}
// Iterate backwards: safe when once()/off() splice() during emission since
// removals only shift elements at higher indices (already visited).
// Zero allocations vs the previous listeners.slice() snapshot approach.
for (let i = listeners.length - 1; i >= 0; i--) {
listeners[i](this, data);
}
}
/**
* Check whether this emitter has any listeners registered.
*
* @param event - Optional event name. When provided, checks only that
* event. When omitted, checks all events.
* @returns `true` if at least one listener is registered.
*/
hasListeners(event) {
const map = this.eventListeners;
if (map === null) {
return false;
}
if (event !== undefined) {
const listeners = map[event];
return listeners !== undefined && listeners.length > 0;
}
for (const key in map) {
const listeners = map[key];
if (listeners !== undefined && listeners.length > 0) {
return true;
}
}
return false;
}
removeAllListeners() {
this.eventListeners = null;
}
/**
* Clear all listeners for the given event names by setting their array
* length to 0, WITHOUT deleting the keys. This keeps the eventListeners
* object in V8's fast-properties mode and avoids re-allocating the arrays
* on the next on() call. Use this for objects with a known fixed set of
* event names (e.g. CoreAnimation, CoreAnimationController).
*
* Only writes arr.length = 0 when the array is non-empty -- skips the write
* (and the write barrier on old-gen objects) when already empty, which is
* the common case after unregisterAnimation() has removed all listeners.
*/
clearListeners(events) {
const map = this.eventListeners;
if (map === null) {
return;
}
for (let i = 0; i < events.length; i++) {
const arr = map[events[i]];
if (arr !== undefined && arr.length > 0) {
arr.length = 0;
}
}
}
}
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