如何用量角器检查元素是否存在？(How to check if element is present with protractor?)

 我为Angular2应用程序编写了以下量角器测试： 
 
describe('Puppet container', () => {

  beforeEach(() => {
    browser.get('/#/puppet');
  });

  it('should display puppet summary', () => {
    browser.wait($('puppet-summary').isPresent, 1000);

    const subject = $('puppet-summary').isDisplayed();
    const result = true;

    expect(subject).toEqual(result);
  });

});
 
 它因以下原因而Failed: Cannot read property 'parentElementArrayFinder' of undefined ： Failed: Cannot read property 'parentElementArrayFinder' of undefined 
 
 谁能告诉我为什么我会收到这个错误？ 我有一个页面，只有在加载后端数据时才会显示<puppet-summary>元素。 这就是为什么我要检查它是否存在（它只在半秒左右后出现）。 要仅在有数据显示时显示，我使用以下HTML代码： 
 
<div *ngIf="puppetMasters.length">
    <puppet-summary></puppet-summary>
</div>
 
 puppetMasters是一个数组，一旦加载后端数据就会被填充。 

I wrote the following protractor test for an Angular2 app:
 
describe('Puppet container', () => {

  beforeEach(() => {
    browser.get('/#/puppet');
  });

  it('should display puppet summary', () => {
    browser.wait($('puppet-summary').isPresent, 1000);

    const subject = $('puppet-summary').isDisplayed();
    const result = true;

    expect(subject).toEqual(result);
  });

});
 
It keeps failing with the following reason: Failed: Cannot read property 'parentElementArrayFinder' of undefined
 
Can anybody tell me why I'm getting this error? I have a page which only shows the <puppet-summary> element when the data from the backend is loaded. That's why I'm checking for it to be present (it only becomes present after half a second or so). To show it only if there is data to display, I'm using the following HTML code:
 
<div *ngIf="puppetMasters.length">
    <puppet-summary></puppet-summary>
</div>
 
puppetMasters is an array which gets filled as soon as the data from the backend is loaded.

原文：https://stackoverflow.com/questions/37070489