The event handler method receives the following arguments:
sender
A TabControl instance, which is the source of the event. This object will be passed to the handler function as the first argument.
args
A SelectedItemChangingEventArgs instance, which contains event data. This object will be passed to the handler function as the second argument.

The cancel property of the SelectedItemChangingEventArgs class lets you stop the action.

The following code creates a calendar and handles its selectedDateChanging event:

JavaScript  Copy Code
var calendar = new ui.Calendar(document.querySelector("#cal")); calendar.theme = "gray"; calendar.selectedDateChanging.addEventListener(handleValueChanging); calendar.render(); function handleValueChanging(sender, args) {     if (sender == calendar)     {         args.cancel = true;     }  }

Calendar Members
Calendar Class
MindFusion.Common.UI Namespace