Question

How can I get the object in the appointments array, where appointments.id = calEvent.id?

appointments.push({
  id: id,
  start: startFormatted,
  end: endFormatted, 
  title: '<b>' + title + '</b><br><div id="event_body">' + body + '</div>', 
  userId: userid,
  categoryId: categoryId,
  counterId: counter
});

eventRender : function(calEvent, $event) {
  var id = calEvent.id;

  // get the object in the appointments-array where appointments.id = calEvent.id
}

Answer 1

You need to loop through your appointments array an find the matching id. Try this:

eventRender : function(calEvent, $event) {
    var id = calEvent.id;        
    for (var i = 0; i < appointments.length; i++) {
        if (appointments[i].id == id) {
            // do something with the appointment...
            break;
        }
    }
}