jQuery Fullcalendar 2.0.0 prevent intervals ovelapping

// isOverlapping function taken from http://stackoverflow.com/a/25691209/1057527
calendar = $('#calendar').fullCalendar({
    // code
    eventDrop: function(event, revertFunc) {
        if (isOverlapping(event)) {
            revertFunc();
        }
    },
    eventResize: function(event, revertFunc) {
        if (isOverlapping(event)) {
            revertFunc();
        }
    },
    // code
});

function isOverlapping(event){
   var array = calendar.fullCalendar('clientEvents');
   for(i in array){
       if(array[i]._id != event._id){
           if(!(array[i].start.format() >= event.end.format() || array[i].end.format() <= event.start.format())){
               return true;
           }
       }
    }
    return false;
}