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/**
* @license
* Copyright (C) 2019 The Android Open Source Project
*
* 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.
*/
/**
* An lite implementation of
* https://nodejs.org/api/events.html#events_class_eventemitter.
*
* This is unrelated to the native DOM events, you should use it when you want
* to enable EventEmitter interface on any class.
*
* @example
*
* class YourClass extends EventEmitter {
* // now all instance of YourClass will have this EventEmitter interface
* }
*
*/
export class EventEmitter {
constructor() {
/**
* Shared events map from name to the listeners.
*
* @type {!Object<string, Array<eventCallback>>}
*/
this._listenersMap = new Map();
}
/**
* Register an event listener to an event.
*
* @param {string} eventName
* @param {eventCallback} cb
* @returns {Function} Unsubscribe method
*/
addListener(eventName, cb) {
if (!eventName || !cb) {
console.warn('A valid eventname and callback is required!');
return;
}
const listeners = this._listenersMap.get(eventName) || [];
listeners.push(cb);
this._listenersMap.set(eventName, listeners);
return () => {
this.off(eventName, cb);
};
}
// Alias for addListener.
on(eventName, cb) {
return this.addListener(eventName, cb);
}
// Attach event handler only once. Automatically removed.
once(eventName, cb) {
const onceWrapper = (...args) => {
cb(...args);
this.off(eventName, onceWrapper);
};
return this.on(eventName, onceWrapper);
}
/**
* De-register an event listener to an event.
*
* @param {string} eventName
* @param {eventCallback} cb
*/
removeListener(eventName, cb) {
let listeners = this._listenersMap.get(eventName) || [];
listeners = listeners.filter(listener => listener !== cb);
this._listenersMap.set(eventName, listeners);
}
// Alias to removeListener
off(eventName, cb) {
this.removeListener(eventName, cb);
}
/**
* Synchronously calls each of the listeners registered for
* the event named eventName, in the order they were registered,
* passing the supplied detail to each.
*
* Returns true if the event had listeners, false otherwise.
*
* @param {string} eventName
* @param {*} detail
*/
emit(eventName, detail) {
const listeners = this._listenersMap.get(eventName) || [];
for (const listener of listeners) {
try {
listener(detail);
} catch (e) {
console.error(e);
}
}
return listeners.length !== 0;
}
// Alias to emit.
dispatch(eventName, detail) {
return this.emit(eventName, detail);
}
/**
* Remove listeners for a specific event or all.
*
* @param {string} eventName if not provided, will remove all
*/
removeAllListeners(eventName) {
if (eventName) {
this._listenersMap.set(eventName, []);
} else {
this._listenersMap = new Map();
}
}
}