<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/markdownToolbar.min.js">

<script src="https://cdn.quilljs.com/1.3.1/quill.js"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/markdownToolbar.min.js">
<script>
  const toolbarOptions = {
      container: [
        ['bold', 'italic', 'underline', 'strike'],
        ['markdown'], // Add this.
      ],
      handlers: { // Add this.
      'markdown': function () {} 
      }
    };

  var quill = new Quill('#editor', {
    theme: 'snow',
    modules: {
      toolbar: toolbarOptions,
      'markdown-toolbar': true // Add this.
    }
  });
</script>