How to use the @jupyter-widgets/controls.SelectionModel.prototype function in @jupyter-widgets/controls

function clone(obj) {
  return JSON.parse(JSON.stringify(obj));
};

const States = {
  unselected: 0,
  selected: 1,
  mixed: 2,
  empty: 3
};

// TreeModel

var TreeModel = SelectionModel.extend({
  defaults: extend(SelectionModel.prototype.defaults(), {
    _model_name: 'TreeModel',
    _view_name: 'TreeView',
    _model_module: 'jupyter_cadquery',
    _view_module: 'jupyter_cadquery',
    _model_module_version: "v0.9.5",
    _view_module_version: "v0.9.5",
    icons: null,
    tree: null,
    state: null
  })
});


// TreeView

var TreeView = DescriptionView.extend({