FroalaEditor.DefineIcon('buttonIcon', { NAME: 'star'})

FroalaEditor.RegisterCommand('myButton', {
  title: 'My Button',
  icon: 'buttonIcon',
  undo: true,
  focus: true,
  showOnMobile: true,
  refreshAfterCallback: true,
  callback: function () {
    console.log (this.html.get());
  },
  refresh: function ($btn) {
    console.log (this.selection.element());
  }
})


<script defer data-domain="html.cafe" src="https://milkymouse.com/js/script.js"></script>