如何使用新功能扩展 UiApp？

我想使用包装函数在 Google Apps 脚本中扩展（原型）UiApp，但在运行如下所示的简单示例时出现 TypeError... 我究竟做错了什么？

Object.prototype.addLabel = function(text) {   
  this.createLabel(text);
  return this;
}

function testingxUiApp() {
  var doc = SpreadsheetApp.getActiveSpreadsheet();
  var app = UiApp.createApplication().setTitle('playing around UiApp').setHeight("250");
  var panel = app.createFlowPanel().setId('panel');
  app.add(panel);
  panel.add(app.addLabel("adding label for testing"));
  doc.show(app);
}

thanks

无法扩展UiApp、Document、Spreadsheet 等高阶类。谷歌阻止了它。如果要执行var isObject = UiApp.createApplication() instanceof Object;行然后isObject是假的，尽管typeof UiApp.createApplication();表达式返回object.