When using the Fullcalender-Libary you can, by default, have several events happening at the same time for a single resource. Hence, it can sometimes be needed to only have one event at a time (e.g. One person can only be at one event at a time...) I wonder whether you can restrict the overlapping/paralleling of events on input. Meaning that onyl one event can be entered for one resource at one time.
Use Async/Await or Promises so that one call or one method must wait for another to be finished.