event-emitters/dist.es2018/EventEmitter.js

event emitters

import { EventEmitterAsyncIterator } from './EventEmitterAsyncIterator';
/**
 * The same as node's EventEmitter but:
 * Only emits a single "event".
 * Throw an exception when a client registers the same listener more than once.
 * Throw an exception when a client tries to remove a listener that is not listening.
 */
export class EventEmitter {
    constructor() {
        this.listeners = [];
    }
    emit(newMessage) {
        this.listeners.forEach((listener) => {
            listener(newMessage);
        });
    }
    subscribe(listener) {
        if (this.listeners.includes(listener)) {
            throw new Error('You have already subscribed with this listener');
        }
        this.listeners.push(listener);
        return listener;
    }
    unsubscribe(listener) {
        const index = this.listeners.indexOf(listener);
        if (index === -1) {
            throw new Error('Tried to remove listener that is not listening');
        }
        this.listeners.splice(index, 1);
    }
    hasListeners() {
        return this.listeners.length !== 0;
    }
    [Symbol.asyncIterator]() {
        return this.asyncIterator();
    }
    asyncIterator() {
        return new EventEmitterAsyncIterator(this);
    }
}
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