ES6 small event system in 30 LOC

Eventify.js

/**
 * Basic event system. Use in component or as event bus
 * Author: Chris Panayotoff <chris.panayotoff[at]gmail[dot]com>
 */

export default class Eventify {
  constructor() {
    this.list = {};
  }

  trigger(event, eventObject = {}) {
    eventObject._name = event;
    if (!this.list[event]) return;
    for (const handlerObject of this.list[event]) {
      handlerObject.handler(eventObject);
      handlerObject.once && this.off(event, handlerObject.handler);
    }
  }

  on(event, handler, once = false) {
    if (!this.list[event]) this.list[event] = [];
    this.list[event].push({ once: once, handler: handler });
  }

  once(event, handler) {
    this.on(event, handler, true);
  }
  
  off(event, handler) {
    if (!event) this.list = {};
    if (!this.list[event]) return;
    if (!handler) this.list[event] = [];

    const indexToRemove = this.list[event].findIndex(
      eventObject => eventObject.handler === handler
    );
    indexToRemove > -1 && this.list[event].splice(indexToRemove, 1);
  }
}