Edit in JSFiddle

document.addEventListener("DOMContentLoaded", function() {

  new FancyForm({
    renderTo: 'container',
    title: 'Combo MultiSelect',
    width: 285,
    height: 300,
    items: [{
      type: 'combo',
      multiSelect: true,
      label: 'MultiSelect',
      data: [
        {index: 'us', country: 'USA'},
        {index: 'ca', country: 'Canada'},
        {index: 'br', country: 'Brazil'}
      ],
      displayKey: 'country',
      valueKey: 'index',
      value: ['us', 'br']
    },{
      type: 'combo',
      multiSelect: true,
      itemCheckBox: true,
      label: 'CheckBoxes',
      data: [
        {index: 'us', country: 'USA'},
        {index: 'ca', country: 'Canada'},
        {index: 'br', country: 'Brazil'}
      ],
      displayKey: 'country',
      valueKey: 'index',
      value: ['us', 'br']
    }]
  });

});

<script src="https://cdn.fancygrid.com/fancy.min.js"></script>

<div id="container"></div>