class EventBus<DetailType = any> {
  private eventTarget: EventTarget;
  constructor(description = '') { this.eventTarget = document.appendChild(document.createComment(description)); }
  on(type: string, listener: (event: CustomEvent<DetailType>) => void) { this.eventTarget.addEventListener(type, listener); }
  once(type: string, listener: (event: CustomEvent<DetailType>) => void) { this.eventTarget.addEventListener(type, listener, { once: true }); }
  off(type: string, listener: (event: CustomEvent<DetailType>) => void) { this.eventTarget.removeEventListener(type, listener); }
  emit(type: string, detail?: DetailType) { return this.eventTarget.dispatchEvent(new CustomEvent(type, { detail })); }
}

// Usage
const myEventBus = new EventBus<string>('my-event-bus');
myEventBus.on('event-name', ({ detail }) => {
    document.body.append(detail + ' ');
});
myEventBus.once('event-name', ({ detail }) => {
    document.body.append(detail + ' ');
});
myEventBus.emit('event-name', 'Hello'); // => Hello Hello
myEventBus.emit('event-name', 'World'); // => World