JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://fullcalendar.io/js/fullcalendar-3.2.0/fullcalendar.min.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/moment.js/2.9.0/moment.min.js"></script>
<script src="https://fullcalendar.io/js/fullcalendar-3.2.0/fullcalendar.min.js"></script>
<div id="calendar">
</div>

JavaScript

var todayDate = moment().startOf('day');
	var YM = todayDate.format('YYYY-MM');
	var YESTERDAY = todayDate.clone().subtract(1, 'day').format('YYYY-MM-DD');
	var TODAY = todayDate.format('YYYY-MM-DD');
	var TOMORROW = todayDate.clone().add(1, 'day').format('YYYY-MM-DD');
$("#calendar").fullCalendar({
		header: {
			left: 'prev,next today',
			center: 'title',
			right: 'month,agendaWeek,agendaDay,listWeek'
		},
		editable: true,
		eventLimit: true, // allow "more" link when too many events
		navLinks: true,
		events: [
			{
				title: 'All Day Event',
				start: '2018-09-07'
			},
			{
				title: 'Long Event',
				start: '2018-09-07T12:00',
				end: '2018-09-07T13:00'
			}
		]
	})
  var items = [
    {
        title: 'Event added (it works)',
        start: '2018-09-07'
    }, {
        title: 'Event added again (it\'s done)',
        start: '2018-09-07',
        end: '2018-09-08'
    }
];
for ( var i = 0; i < items.length; i++ ) {
    $('#calendar').fullCalendar( 'renderEvent', items[i]);
}