puppeteer-core
Version:
A high-level API to control headless Chrome over the DevTools Protocol
126 lines • 4.15 kB
JavaScript
/**
* Copyright 2022 Google Inc. All rights reserved.
*
* 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.
*/
import mitt from '../../third_party/mitt/index.js';
/**
* The EventEmitter class that many Puppeteer classes extend.
*
* @remarks
*
* This allows you to listen to events that Puppeteer classes fire and act
* accordingly. Therefore you'll mostly use {@link EventEmitter.on | on} and
* {@link EventEmitter.off | off} to bind
* and unbind to event listeners.
*
* @public
*/
export class EventEmitter {
/**
* @internal
*/
constructor() {
this.eventsMap = new Map();
this.emitter = mitt(this.eventsMap);
}
/**
* Bind an event listener to fire when an event occurs.
* @param event - the event type you'd like to listen to. Can be a string or symbol.
* @param handler - the function to be called when the event occurs.
* @returns `this` to enable you to chain method calls.
*/
on(event, handler) {
this.emitter.on(event, handler);
return this;
}
/**
* Remove an event listener from firing.
* @param event - the event type you'd like to stop listening to.
* @param handler - the function that should be removed.
* @returns `this` to enable you to chain method calls.
*/
off(event, handler) {
this.emitter.off(event, handler);
return this;
}
/**
* Remove an event listener.
* @deprecated please use {@link EventEmitter.off} instead.
*/
removeListener(event, handler) {
this.off(event, handler);
return this;
}
/**
* Add an event listener.
* @deprecated please use {@link EventEmitter.on} instead.
*/
addListener(event, handler) {
this.on(event, handler);
return this;
}
/**
* Emit an event and call any associated listeners.
*
* @param event - the event you'd like to emit
* @param eventData - any data you'd like to emit with the event
* @returns `true` if there are any listeners, `false` if there are not.
*/
emit(event, eventData) {
this.emitter.emit(event, eventData);
return this.eventListenersCount(event) > 0;
}
/**
* Like `on` but the listener will only be fired once and then it will be removed.
* @param event - the event you'd like to listen to
* @param handler - the handler function to run when the event occurs
* @returns `this` to enable you to chain method calls.
*/
once(event, handler) {
const onceHandler = eventData => {
handler(eventData);
this.off(event, onceHandler);
};
return this.on(event, onceHandler);
}
/**
* Gets the number of listeners for a given event.
*
* @param event - the event to get the listener count for
* @returns the number of listeners bound to the given event
*/
listenerCount(event) {
return this.eventListenersCount(event);
}
/**
* Removes all listeners. If given an event argument, it will remove only
* listeners for that event.
* @param event - the event to remove listeners for.
* @returns `this` to enable you to chain method calls.
*/
removeAllListeners(event) {
if (event) {
this.eventsMap.delete(event);
}
else {
this.eventsMap.clear();
}
return this;
}
eventListenersCount(event) {
var _a;
return ((_a = this.eventsMap.get(event)) === null || _a === void 0 ? void 0 : _a.length) || 0;
}
}
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