How to use the @lumino/widgets.StackedPanel function in @lumino/widgets

function createWrapper(content: Widget, title: string): Widget {
  let wrapper = new StackedPanel();
  wrapper.addClass('content-wrapper');
  wrapper.addWidget(content);
  wrapper.title.label = title;
  return wrapper;
}

constructor() {
      this._sideBar = new TabBarSvg({
        kind: 'sideBar',
        insertBehavior: 'none',
        removeBehavior: 'none',
        allowDeselect: true
      });
      this._stackedPanel = new StackedPanel();
      this._sideBar.hide();
      this._stackedPanel.hide();
      this._lastCurrent = null;
      this._sideBar.currentChanged.connect(this._onCurrentChanged, this);
      this._sideBar.tabActivateRequested.connect(
        this._onTabActivateRequested,
        this
      );
      this._stackedPanel.widgetRemoved.connect(this._onWidgetRemoved, this);
    }