Micro EventEmitter v2

micro-events.js

/**
 * micro event emitter
 * @author [email protected]
 * @gist https://gist.github.com/mikepuerto/1418a024ab93e1cb353305c9ceadfbde
 */

class EventEmitter {

  constructor() {
    this._eventHandlers = {};
  }

  on(event, callback, once = false) {
    this._eventHandlers[event] = this._eventHandlers[event] || [];
    this._eventHandlers[event].push({ callback, once });
  }

  once(event, callback) {
    this.on(event, callback, true);
  }

  off(event, callback) {
    if (!this._eventHandlers[event]) {
      return;
    }

    this._eventHandlers[event].forEach((eventHandler, idx) => {
      if (eventHandler.callback === callback) {
        this._eventHandlers[event].splice(idx, 1);
      }
    });

    return true;

  }

  emit(event, data) {
    if (!this._eventHandlers[event] || !this._eventHandlers[event].length) {
      return undefined;
    }

    const args = [].slice.call(arguments, 1);

    this._eventHandlers[event].forEach(handler => {
      handler.callback.apply(handler.callback, args);
      handler.once && this.off(event, handler.callback);
    });

  }

}

export default EventEmitter;