Event Bus Typescript

event_bus.ts

import { EventEmitter } from 'eventemitter3';

type ListenerFn = (...args: Array<any>) => void;

class EventBus {
  public eventEmitter: EventEmitter;
  /**
   * Initiate the event emitter
   */
  constructor() {
    this.eventEmitter = new EventEmitter();
  }

  /**
   * Adds the listener function to the end of the listeners array for
   * the event named eventName. No checks are made to see if the listener
   * has already been added. Multiple calls passing the same combination of
   * eventName and listener will result in the listener being added, and called,
   * multiple times.
   *
   * @param {string} eventName
   * @param {function} listener
   * @param {any} context
   */
  public addEventListener(eventName: string, listener: ListenerFn, context?: any): void {
    this.eventEmitter.on(eventName, listener, context);
  }

  /**
   * Removes the specified listener from the listener array for the event named eventName.
   *
   * @param {string} eventName
   * @param {function} listener
   * @param {any} context
   * @param {boolean} once
   */
  public removeEventListener(eventName: string, listener?: ListenerFn, context?: any, once?: boolean): void {
    this.eventEmitter.off(eventName, listener, context, once);
  }

  /**
   * Synchronously calls each of the listeners registered for the event
   * named eventName, in the order they were registered,
   * passing the supplied arguments to each.
   *
   * @param {string} eventName
   * @param {array} args
   */
  public emit(eventName: string, ...args: Array<any>): void {
    this.eventEmitter.emit(eventName, ...args);
  }

  /**
   * Returns the event emitter
   * Used for testing purpose and avoid using this during development
   */
  public getEventEmitter(): EventEmitter {
    return this.eventEmitter;
  }

  /**
   * Adds a one-time listener function for the event named eventName.
   * The next time eventName is triggered, this listener is removed and then invoked.
   *
   * @param {string} eventName
   * @param {ListenerFn} listener
   * @param {any} context
   */
  public once(eventName: string, listener: ListenerFn, context?: any): void {
    this.eventEmitter.once(eventName, listener, context);
  }
}

export const eventBusClient = new EventBus();