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/**
* 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, {Emitter, EventHandlerMap} from '../../third_party/mitt/index.js';
/**
* @public
*/
export type EventType = string | symbol;
/**
* @public
*/
export type Handler<T = unknown> = (event: T) => void;
/**
* @public
*/
export interface CommonEventEmitter {
on(event: EventType, handler: Handler): CommonEventEmitter;
off(event: EventType, handler: Handler): CommonEventEmitter;
/* To maintain parity with the built in NodeJS event emitter which uses removeListener
* rather than `off`.
* If you're implementing new code you should use `off`.
*/
addListener(event: EventType, handler: Handler): CommonEventEmitter;
removeListener(event: EventType, handler: Handler): CommonEventEmitter;
emit(event: EventType, eventData?: unknown): boolean;
once(event: EventType, handler: Handler): CommonEventEmitter;
listenerCount(event: string): number;
removeAllListeners(event?: EventType): CommonEventEmitter;
}
/**
* 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 implements CommonEventEmitter {
private emitter: Emitter<Record<string | symbol, any>>;
private eventsMap: EventHandlerMap<Record<string | symbol, any>> = new Map();
/**
* @internal
*/
constructor() {
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: EventType, handler: Handler<any>): EventEmitter {
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: EventType, handler: Handler<any>): EventEmitter {
this.emitter.off(event, handler);
return this;
}
/**
* Remove an event listener.
* @deprecated please use {@link EventEmitter.off} instead.
*/
removeListener(event: EventType, handler: Handler<any>): EventEmitter {
this.off(event, handler);
return this;
}
/**
* Add an event listener.
* @deprecated please use {@link EventEmitter.on} instead.
*/
addListener(event: EventType, handler: Handler<any>): EventEmitter {
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: EventType, eventData?: unknown): boolean {
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: EventType, handler: Handler<any>): EventEmitter {
const onceHandler: Handler<any> = 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: EventType): number {
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?: EventType): EventEmitter {
if (event) {
this.eventsMap.delete(event);
} else {
this.eventsMap.clear();
}
return this;
}
private eventListenersCount(event: EventType): number {
return this.eventsMap.get(event)?.length || 0;
}
}
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