index.js

import { app, BrowserWindow, Menu, dialog } from 'electron';
...
  mainWindow = null;
  });

   const showMessage = message => dialog.showMessageBox({
    type: 'info',
    message: `You activated action: "${message}"`,
    buttons: ['Close'],
  });

   const menu = Menu.buildFromTemplate([
    {
      label: 'Preferences',
      submenu: [
        {
          label: 'Prefer Dark Theme',
          type: 'checkbox',
        },
        {
          label: 'Hide Titlebar when maximized',
          type: 'checkbox',
        },
        {
          label: 'Color',
          submenu: [
            {
              label: 'Red',
              type: 'radio',
              accelerator: 'CmdOrCtrl+R',
              click: () => showMessage('Red'),
            },
            {
              label: 'Green',
              type: 'radio',
              accelerator: 'CmdOrCtrl+G',
              click: () => showMessage('Green'),
            },
            {
              label: 'Blue',
              type: 'radio',
              accelerator: 'CmdOrCtrl+B',
              click: () => showMessage('Blue'),
            },
          ],
        },
        {
          label: 'Shape',
          submenu: [
            {
              label: 'Square',
              type: 'radio',
              accelerator: 'CmdOrCtrl+S',
              click: () => showMessage('Square'),
            },
            {
              label: 'Rectangle',
              type: 'radio',
              accelerator: 'CmdOrCtrl+R',
              click: () => showMessage('Rectangle'),
            },
            {
              label: 'Oval',
              type: 'radio',
              accelerator: 'CmdOrCtrl+O',
              click: () => showMessage('Oval'),
            },
          ],
        },
        {
          label: 'Bold',
          type: 'checkbox',
          accelerator: 'CmdOrCtrl+Shift+B',
          click: () => showMessage('Bold'),
        },
      ],
    },
    {
      label: 'Help',
      submenu: [
        {
          label: 'About',
          accelerator: 'CmdOrCtrl+A',
          click: () => dialog.showMessageBox({
            type: 'info',
            title: 'about',
            message: `GTK+ Code Demos
3.22.30
Running against GTK+ 3.22.30
Program to demonstrate GTK+ functions.
(C) 1997-2013 The GTK+ Team
This program comes with absolutely no warranty.
See the GNU Lesser General Public License, 
version 2.1 or later for details.`,
            buttons: ['Close'],
          }),
        },
      ],
    },
  ]);
  Menu.setApplicationMenu(menu);
...