code: func (e *eventer) Once(n string, f func(s interface{})) (err error) {
  	out := e.Subscribe()
  	go func() {
  	ProcessEvents:
  		for evt := range out {
  			if evt.Name == n {
  				f(evt.Data)
  				e.Unsubscribe(out)
  				break ProcessEvents
  			}
  		}
  	}()
  
  	return
  }
docs: // Once is similar to On except that it only executes f one time.