minimal-pubsub.js

/**
 * Minimal Pub/Sub class
 *
 * @class EventEngine
 */
class EventEngine {
    /**
     * Creates an instance of EventEngine.
     * @memberof EventEngine
     */
    constructor() {
        this.eventHandler = {};
    }

    /**
     * Attach an event handler to an event name
     *
     * @param {*} eventName
     * @param {*} handler
     * @returns
     * @memberof EventEngine
     */
    on(eventName, handler) {
        if (!eventName || !handler) { return; }
        if (!this.eventHandler[eventName]) { this.eventHandler[eventName] = []; }
        this.eventHandler[eventName].push(handler);
    }

    /**
     * Removes a single event handler if specified, 
     * otherwise removes all event handlers for a given event
     *
     * @param {*} eventName
     * @param {*} handler
     * @returns
     * @memberof EventEngine
     */
    off(eventName, handler) {
        if (!eventName || !this.eventHandler[eventName]) { return; }
        
        if (typeof (handler) === "function") {
            // Remove a single event handler for {eventName}
            var idx = this.eventHandler[eventName].indexOf(handler);
            
            if (idx > -1) {
                this.eventHandler[eventName].splice(idx, 1);
            }
        }
        else {
            // Remove all event handlers for {eventName}
            this.eventHandler[eventName] = [];
        }
    }

    /**
     * Trigger an event. Optionally pass argument(s) and/or scope
     *
     * @param {*} eventName
     * @param {*} eventData
     * @param {*} eventScope
     * @returns
     * @memberof EventEngine
     */
    trigger(eventName, eventData, eventScope) {
        if (!this.eventHandler[eventName]) return;
        
        this.eventHandler[eventName].forEach((func) => {
            if (typeof (func) === "function") {
                // eventScope and eventData - when left undefined, will run OK
                func.apply(eventScope, eventData);
            }
        });
    }
}

module.exports = EventEngine;