在Cypress中选择某个元素内部的第n个子元素，可以使用.children()来获取所有子元素，然后使用.eq(index)来选取特定索引的子元素。索引是从0开始的，所以如果您想选择第n个子元素，您需要使用.eq(n-1)。这里有一个具体的例子：

假设我们有如下的HTML结构：

html
<div class="parent">
  <div class="child">Child 1</div>
  <div class="child">Child 2</div>
  <div class="child">Child 3</div>
</div>

如果你想选择这个父元素内的第二个子元素，你可以这样写Cypress测试代码：

javascript
cy.get('.parent').children().eq(1).should('contain', 'Child 2');

在这个例子中：

• .get('.parent') 选择了类名为parent的元素。
• .children() 获取了这个父元素的所有直接子元素。
• .eq(1) 选择了这些子元素中的第二个（索引为1）。
• .should('contain', 'Child 2') 是断言，检查选中的元素是否包含文本"Child 2"。

如果您想选择第n个子元素，请确保将n减去1，然后放在.eq()中，因为索引是基于0的。

Update

As pointed out by @dpstree in the comments, this doesn't answer the original question. Please see more recent answers for a complete solution.

Original

By using eq

shell
cy.get('tbody>tr').eq(0)    // Yield first 'tr' in 'tbody'
cy.get('ul>li').eq(4)       // Yield fifth 'li' in 'ul'

In the particular context of selecting the nth option, this may be appropriate:

shell
cy.get('select[name=subject] > option')
  .eq(3)
  .then(element => cy.get('select[name=subject]').select(element.val()))

Based on solution from Miguel Rueda, but using prevSubject option:

shell
Cypress.Commands.add(
  'selectNth',
  { prevSubject: 'element' },
  (subject, pos) => {
    cy.wrap(subject)
      .children('option')
      .eq(pos)
      .then(e => {
        cy.wrap(subject).select(e.val())
      })
  }
)

Usage:

shell
cy.get('[name=assignedTo]').selectNth(2)

Explanation:

• Using children('option') and .eq(pos) traverse children of select to specific element.
• Call select method with value of selected element.

You can now select an option by index within the .select(index) command:

shell
cy.get('select').select(0)        // selects by index (yields first option) ie "What is this regarding?"
cy.get('select').select([0, 1])   // select an array of indexes

This should be easy now with the release of cypress v8.5.0. See documentation for more.

I had the same problem and solved it by creating a custom cypress command. No as pretty as I would like, but it did the job.

shell
Cypress.Commands.add("selectNth", (select, pos) => {
  cy.get(`${select} option +option`)
    .eq(pos)
    .then( e => {
       cy.get(select)
         .select(e.val())
    })
})

then I used in the test as such

shell
    cy.viewport(375, 667)
      .selectNth("customSelector", 3)

The option +option part was the only way I could find to get the full list of options inside a select and it's currently the bit of code i'm trying to work arround although it works fine.