How to use the nbdime/lib/merge/widget.NotebookMergeWidget function in nbdime

function showMerge(data: {
    base: nbformat.INotebookContent,
    merge_decisions: IMergeDecision[]
    }): Promise {

  let rendermime = new RenderMimeRegistry({
    initialFactories: rendererFactories,
    sanitizer: defaultSanitizer,
  });

  let nbmModel = new NotebookMergeModel(data.base,
      data.merge_decisions);
  let nbmWidget = new NotebookMergeWidget(nbmModel, rendermime);

  let root = document.getElementById('nbdime-root');
  if (!root) {
    throw new Error('Missing root element "nbidme-root"');
  }
  root.innerHTML = '';
  // Hide unchanged cells by default:
  toggleShowUnchanged(!getConfigOption('hideUnchanged', true));

  let panel = new Panel();
  panel.id = 'main';
  Widget.attach(panel, root);
  panel.addWidget(nbmWidget);
  let work = nbmWidget.init();
  work.then(() => {
    window.onresize = () => { panel.update(); };