nests/esm/EventEmitter.js

Fast and easy state storage with a lot of control.

import Events from "./Events";
export default class EventEmitter {
    constructor() {
        this.listeners = Object.values(Events).reduce((acc, val) => ((acc[val] = new Set()), acc), {});
        this.on = function (event, listener) {
            if (this.listeners[event].has(listener)) {
                throw Error(`This listener on ${event} already exists.`);
            }
            this.listeners[event].add(listener);
        };
        this.once = function (event, listener) {
            const onceListener = (event, data) => {
                this.off(event, onceListener);
                listener(event, data);
            };
            this.on(event, onceListener);
        };
        this.off = function (event, listener) {
            this.listeners[event].delete(listener);
        };
        this.emit = function (event, data) {
            for (const listener of this.listeners[event]) {
                listener(event, data);
            }
        };
        for (const event of Object.values(Events)) {
            this[event.toLowerCase()] = (data) => {
                this.emit(event, data);
            };
        }
    }
}