title: onDragStop tells me jsEvent is undefined
body: <p>I'm trying to make it possible to drag events to an external div and back into the calendar again. However, whenever I drop an event I get TypeError: jsEvent is undefined.</p>
  
  <p>I'm not entirely sure why it is doing this, this should be a valid parameter that is passed to the function of eventDragStop.</p>
  
  <p>I'm using the latest FullCalendar 4.</p>
  
  <p>Here is my code</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>// Load the CSS stuff
  import {Tooltip} from "bootstrap";
  
  require('@fortawesome/fontawesome-free/css/fontawesome.min.css');
  require('@fortawesome/fontawesome-free/css/brands.min.css');
  require('@fortawesome/fontawesome-free/css/solid.min.css');
  require('../css/app.scss');
  
  // Load the JS stuff
  let $ = require('jquery');
  require('bootstrap');
  require('./libs/navbar.js');
  require('jquery-ui/ui/widgets/draggable');
  import apiclient from "./libs/apiclient";
  import { Calendar } from '@fullcalendar/core';
  import dayGridPlugin from '@fullcalendar/daygrid';
  import timeGridPlugin from '@fullcalendar/timegrid';
  import interactionPlugin from '@fullcalendar/interaction';
  import bootstrapPlugin from '@fullcalendar/bootstrap';
  
  // $(document).ready(function () {
  //
  // });
  
  document.addEventListener('DOMContentLoaded', () =&gt; {
      /* initialize the external events
          -----------------------------------------------------------------*/
  
      $('#external-events .fc-event').each(function() {
  
          // store data so the calendar knows to render an event upon drop
          $(this).data('event', {
              title: $.trim($(this).text()), // use the element's text as the event title
              stick: true // maintain when user navigates (see docs on the renderEvent method)
          });
  
          // make the event draggable using jQuery UI
          $(this).draggable({
              zIndex: 999,
              revert: true,      // will cause the event to go back to its
              revertDuration: 0  //  original position after the drag
          });
  
      });
      let calendarEl = document.getElementById('calendar-holder');
  
      let calendar = new Calendar(calendarEl, {
          views: {
              jira: {
                  type: 'dayGridWeek',
                  duration: {months: 3},
                  buttonText: 'Jira'
              }
          },
          defaultView: 'jira',
          themeSystem: 'bootstrap',
          editable: true,
          droppable: true,
          firstDay: 1,
          contentHeight: 'auto',
          weekNumbersWithinDays: true,
          weekNumbers: true,
          eventSources: [
              {
                  url: "/fc-load-events",
                  method: "POST",
                  extraParams: {
                      filters: JSON.stringify({})
                  },
                  failure: () =&gt; {
                      // alert("There was an error while fetching FullCalendar!");
                  },
              },
          ],
          header: {
              left: 'prev,next today',
              center: 'title',
              right: 'jira,dayGridMonth,timeGridWeek',
          },
          plugins: [ bootstrapPlugin, interactionPlugin, dayGridPlugin, timeGridPlugin ], // https://fullcalendar.io/docs/plugin-index
          timeZone: 'UTC',
          eventRender: function(info) {
              var tooltip = new Tooltip(info.el, {
                  title: info.event.title+'&lt;br&gt;'+info.event.extendedProps.assignee,
                  placement: 'top',
                  trigger: 'hover',
                  container: 'body',
                  html: true
              });
          },
          dragRevertDuration: 0,
          drop: function() {
              // is the "remove after drop" checkbox checked?
              if ($('#drop-remove').is(':checked')) {
                  // if so, remove the element from the "Draggable Events" list
                  $(this).remove();
              }
          },
          eventDragStop: function( event, jsEvent, view ) {
  
              if(isEventOverDiv(jsEvent.clientX, jsEvent.clientY)) {
                  $('#calendar-holder').calendar('removeEvents', event._id);
                  var el = $( "&lt;div class='fc-event'&gt;" ).appendTo( '#external-events-listing' ).text( event.title );
                  el.draggable({
                      zIndex: 999,
                      revert: true,
                      revertDuration: 0
                  });
                  el.data('event', { title: event.title, id :event.id, stick: true });
              }
          }
      });
      calendar.render();
  
      let isEventOverDiv = function(x, y) {
  
          var external_events = $( '#external-events' );
          var offset = external_events.offset();
          offset.right = external_events.width() + offset.left;
          offset.bottom = external_events.height() + offset.top;
  
          // Compare
          if (x &gt;= offset.left
              &amp;&amp; y &gt;= offset.top
              &amp;&amp; x &lt;= offset.right
              &amp;&amp; y &lt;= offset .bottom) { return true; }
          return false;
  
      }
  });</code></pre>
  </div>
  </div>
  </p>