ecsy/src/EventDispatcher.js

Entity Component System in JS

/**
 * @private
 * @class EventDispatcher
 */
export default class EventDispatcher {
  constructor() {
    this._listeners = {};
    this.stats = {
      fired: 0,
      handled: 0,
    };
  }

  /**
   * Add an event listener
   * @param {String} eventName Name of the event to listen
   * @param {Function} listener Callback to trigger when the event is fired
   */
  addEventListener(eventName, listener) {
    let listeners = this._listeners;
    if (listeners[eventName] === undefined) {
      listeners[eventName] = [];
    }

    if (listeners[eventName].indexOf(listener) === -1) {
      listeners[eventName].push(listener);
    }
  }

  /**
   * Check if an event listener is already added to the list of listeners
   * @param {String} eventName Name of the event to check
   * @param {Function} listener Callback for the specified event
   */
  hasEventListener(eventName, listener) {
    return (
      this._listeners[eventName] !== undefined &&
      this._listeners[eventName].indexOf(listener) !== -1
    );
  }

  /**
   * Remove an event listener
   * @param {String} eventName Name of the event to remove
   * @param {Function} listener Callback for the specified event
   */
  removeEventListener(eventName, listener) {
    var listenerArray = this._listeners[eventName];
    if (listenerArray !== undefined) {
      var index = listenerArray.indexOf(listener);
      if (index !== -1) {
        listenerArray.splice(index, 1);
      }
    }
  }

  /**
   * Dispatch an event
   * @param {String} eventName Name of the event to dispatch
   * @param {Entity} entity (Optional) Entity to emit
   * @param {Component} component
   */
  dispatchEvent(eventName, entity, component) {
    this.stats.fired++;

    var listenerArray = this._listeners[eventName];
    if (listenerArray !== undefined) {
      var array = listenerArray.slice(0);

      for (var i = 0; i < array.length; i++) {
        array[i].call(this, entity, component);
      }
    }
  }

  /**
   * Reset stats counters
   */
  resetCounters() {
    this.stats.fired = this.stats.handled = 0;
  }
}