EventEmitter.js•2.2 kB
/**
* Copyright 2022 Google LLC.
* Copyright (c) Microsoft Corporation.
*
* 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 'mitt';
export class EventEmitter {
#emitter = mitt();
on(type, handler) {
this.#emitter.on(type, handler);
return this;
}
/**
* 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
* @return `this` to enable chaining method calls.
*/
once(event, handler) {
const onceHandler = (eventData) => {
handler(eventData);
this.off(event, onceHandler);
};
return this.on(event, onceHandler);
}
off(type, handler) {
this.#emitter.off(type, handler);
return this;
}
/**
* Emits an event and call any associated listeners.
*
* @param event The event to emit.
* @param eventData Any data to emit with the event.
* @return `true` if there are any listeners, `false` otherwise.
*/
emit(event, eventData) {
this.#emitter.emit(event, eventData);
}
/**
* 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.#emitter.all.delete(event);
}
else {
this.#emitter.all.clear();
}
return this;
}
}
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