session-desktop/app/tray_icon.js

const electron = require('electron')
const path = require('path');

const app = electron.app;
const Menu = electron.Menu;
const Tray = electron.Tray;

let trayContextMenu = null;
let tray = null;

function createTrayIcon(getMainWindow, messages) {

  // A smaller icon is needed on macOS
  tray = new Tray(
    process.platform == "darwin" ?
    path.join(__dirname, '..', 'images', 'icon_16.png') :
    path.join(__dirname, '..', 'images', 'icon_256.png'));

  tray.toggleWindowVisibility = function () {
    var mainWindow = getMainWindow();
    if (mainWindow) {
      if (mainWindow.isVisible()) {
        mainWindow.hide();
      } else {
        mainWindow.show();

        // On some versions of GNOME the window may not be on top when restored.
        // This trick should fix it.
        // Thanks to: https://github.com/Enrico204/Whatsapp-Desktop/commit/6b0dc86b64e481b455f8fce9b4d797e86d000dc1
        mainWindow.setAlwaysOnTop(true);
        mainWindow.focus();
        mainWindow.setAlwaysOnTop(false);
      }
    }
    tray.updateContextMenu();
  }

  tray.updateContextMenu = function () {

    var mainWindow = getMainWindow();

    // NOTE: we want to have the show/hide entry available in the tray icon
    // context menu, since the 'click' event may not work on all platforms.
    // For details please refer to:
    // https://github.com/electron/electron/blob/master/docs/api/tray.md.
    trayContextMenu = Menu.buildFromTemplate([
        {
          id: 'toggleWindowVisibility',
          label: messages[mainWindow.isVisible() ? 'hide' : 'show'].message,
          click: tray.toggleWindowVisibility
        },
        {
          id: 'quit',
          label: messages.quit.message,
          click: app.quit.bind(app)
        }
    ]);

    tray.setContextMenu(trayContextMenu);
  }

  tray.on('click', tray.toggleWindowVisibility);

  tray.setToolTip(messages.trayTooltip.message);
  tray.updateContextMenu();

  return tray;
}

module.exports = createTrayIcon;