Prevent add of event after user clicks on the calendar

Is there a way to prevent the the addition of an event to the calendar based on a condition such as an event already existing on the calendar.

I am already running a javascript snippet before the custom popup comes up to add an event when the user clicks to add an event and I can figure out if the event is new or not.

How do I cancel the addition of the event to Prevent the add a new event popup from happening?

Thanks.

Any thoughts anybody? 
Do I need to re-phrase the question?

Hey Leo!

I answered on the other thread, but reading this reminds me that you can conditionally render items with skuid based on whether the row in context is new or not. We’re using that as a way to show certain fields and options when editing an existing appointment, and show other options when creating a new appointment. Shoot me an email if you want to set up a screen meeting, and I’ll show you.

Thanks Matt for your help!

Was able to solve the problem.  Based on this solution:  http://community.skuid.com/skuid/topics/calendar-popup-showing-before-deferred-promise-resolved

If your skuid snippet returns a deferred promise Reject then the skuid popup won’t display.  That is one way of preventing the popup from showing.