Add extra fields to fullcalendar

Here is how I used eventRender to add some categories to each event. Then I can filter events based on category name

eventRender: function(event, element) {
        element.attr("categories",event.categoryname)
    }

Simply awesome calendar

you can include your own non-standard fields in each Event Object. FullCalendar will not modify or delete these fields.,this example help you eventRender

and see Event Object

In version 4 of fullcalendar, to get non-standard field is changed a little bit. Now it accepts just one parameter as Event Object:

 events: [
{
  title: 'My Event',
  start: '2010-01-01',
  description: 'This is a cool event'
}
// more events here
],
eventRender: function(info) {
  console.log(info.event.extendedProps.description);
}

Note: You can access an additional field in this way: info.event.extendedProps.description

Check documentation