MyContextMenu.js:
import { Extension, ContextMenuPopup } from '@eclipse-scout/core';

export default class MyContextMenuPopupExtension extends Extension {
  init() {
    this.extend(ContextMenuPopup.prototype, '_renderMenuItems');
  }
  
  _renderMenuItems(menus, initialSubMenuRendering) {
    ... // modifier version of the function here
  }
}

MyApp.js:
import {App, Extension} from '@eclipse-scout/core';
export default class MyApp extends App {
  _installExtensions() {
    Extension.install([
      'virades.MyContextMenuPopupExtension'
    ]);
  }
}

class MyApp extends RemoteApp {
  _installExtensions() {
    Extension.install([
      'virades.MyContextMenuPopupExtension'
    ]);
  }
}

new MyApp().init();