h5p-lib-controls/src/scripts/mixins/eventful.js

Library for adding user input to web applications

/**
 * @mixin
 */
export const Eventful = () => ({
  listeners: {},

  /**
   * Listen to event
   *
   * @param {string} type
   * @param {function} listener
   * @param {object} [scope]
   *
   * @function
   * @return {Eventful}
   */
  on: function(type, listener, scope) {
    /**
     * @typedef {object} Trigger
     * @property {function} listener
     * @property {object} scope
     */
    const trigger = {
      'listener': listener,
      'scope': scope
    };

    this.listeners[type] = this.listeners[type] || [];
    this.listeners[type].push(trigger);

    return this;
  },

  /**
   * Fire event. If any of the listeners returns false, return false
   *
   * @param {string} type
   * @param {object} [event]
   *
   * @function
   * @return {boolean}
   */
  fire: function(type, event) {
    const triggers = this.listeners[type] || [];

    return triggers.every(function(trigger) {
      return trigger.listener.call(trigger.scope || this, event) !== false;
    });
  },

  /**
   * Listens for events on another Eventful, and propagate it trough this Eventful
   *
   * @param {string[]} types
   * @param {Eventful} eventful
   */
  propagate: function(types, eventful) {
    let self = this;
    types.forEach(type => eventful.on(type, event => self.fire(type, event)));
  }
});