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

constructor(options: Application.IOptions) {
    // Create the application command registry.
    let commands = new CommandRegistry();

    // Create the application context menu.
    let renderer = options.contextMenuRenderer;
    let contextMenu = new ContextMenu({ commands, renderer });

    // Initialize the application state.
    this.commands = commands;
    this.contextMenu = contextMenu;
    this.shell = options.shell;
  }

palette.addItem({ command: 'example:three', category: 'Number' });
  palette.addItem({ command: 'example:four', category: 'Number' });
  palette.addItem({ command: 'example:black', category: 'Number' });
  palette.addItem({ command: 'example:new-tab', category: 'File' });
  palette.addItem({ command: 'example:close-tab', category: 'File' });
  palette.addItem({ command: 'example:save-on-exit', category: 'File' });
  palette.addItem({ command: 'example:open-task-manager', category: 'File' });
  palette.addItem({ command: 'example:close', category: 'File' });
  palette.addItem({ command: 'example:clear-cell', category: 'Notebook Cell Operations' });
  palette.addItem({ command: 'example:cut-cells', category: 'Notebook Cell Operations' });
  palette.addItem({ command: 'example:run-cell', category: 'Notebook Cell Operations' });
  palette.addItem({ command: 'example:cell-test', category: 'Console' });
  palette.addItem({ command: 'notebook:new', category: 'Notebook' });
  palette.id = 'palette';

  let contextMenu = new ContextMenu({ commands });

  document.addEventListener('contextmenu', (event: MouseEvent) => {
    if (contextMenu.open(event)) {
      event.preventDefault();
    }
  });

  contextMenu.addItem({ command: 'example:cut', selector: '.content' });
  contextMenu.addItem({ command: 'example:copy', selector: '.content' });
  contextMenu.addItem({ command: 'example:paste', selector: '.content' });

  contextMenu.addItem({ command: 'example:one', selector: '.p-CommandPalette' });
  contextMenu.addItem({ command: 'example:two', selector: '.p-CommandPalette' });
  contextMenu.addItem({ command: 'example:three', selector: '.p-CommandPalette' });
  contextMenu.addItem({ command: 'example:four', selector: '.p-CommandPalette' });
  contextMenu.addItem({ command: 'example:black', selector: '.p-CommandPalette' });