JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.14.1/moment.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/2.9.0/fullcalendar.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/fullcalendar/2.9.0/fullcalendar.min.js"></script>
<div id='calendar'>

</div>

JavaScript

$('#calendar').fullCalendar({
  defaultView: 'agendaWeek',
  viewRender: renderViewColumns
});

function renderViewColumns(view, element) {
  element.find('th.fc-day-header.fc-widget-header').each(function() {
    var theDate = moment($(this).data('date')); /* th.data-date="YYYY-MM-DD" */
    $(this).html(buildDateColumnHeader(theDate));
  });

  function buildDateColumnHeader(theDate) {
    var container = document.createElement('div');
    var DDD = document.createElement('div');
    var ddMMM = document.createElement('div');
    DDD.textContent = theDate.format('ddd').toUpperCase();
    ddMMM.textContent = theDate.format('DD MMM');
    container.appendChild(DDD);
    container.appendChild(ddMMM);
    return container;
  }
}