Enable Handsontable with checkbox selection and update input ID with selected ITIDs

HTML

<link rel="stylesheet" type="text/css" href="https://cdn.jsdelivr.net/npm/handsontable@6.2.2/dist/handsontable.full.min.css">
<script src="https://cdn.jsdelivr.net/npm/handsontable@5.0.2/dist/handsontable.full.min.js"></script>
<div id="example"></div>
<br />
<input type="text" id="tbITID" />

JavaScript

var ddIM='';

const container = document.getElementById('example');
new Handsontable(container, {
  data: [
    {'Selected':false,'ITID':'1001','CSN':'ABCD1'},
    {'Selected':false,'ITID':'1002','CSN':'ABCD2'}
  ],
  editor: false,
  comments: false,
  contextMenu: false, // disable context menu to change things
  disableVisualSelection: true, // prevent user from visually selecting
  manualColumnResize: false, // prevent dragging to resize columns
  manualRowResize: false,
  columns: [{data:'Selected',type:'checkbox'},
  {data:'ITID'},
  {data:'CSN'}],
  colHeaders: ['', 'Column 2', 'Column 3'],
  afterOnCellMouseDown: function(event, coords, TD) {
    if (coords.row >= 0) {
      if(this.colToProp(coords.col) === 'Selected') {
        if(this.getDataAtCell(coords.row,this.propToCol('Selected')) == false) {
        ddIM = ddIM + this.getDataAtCell(coords.row,this.propToCol('ITID')) + '@@';
        document.getElementById('tbITID').value = ddIM;
        }
        else {
          ddIM = ddIM.replace(this.getDataAtCell(coords.row,this.propToCol('ITID')) + '@@','');
          document.getElementById('tbITID').value = ddIM;
        }
      }
    }
  }
});