How to count a selection of items and get the length in Cypress ？

在Cypress中，您可以利用.its('length')命令来获取选择元素的长度。这个命令会返回被选元素的数量。这个功能经常用于断言，以确保DOM中存在特定数量的元素。

以下是一个例子，假设我们要测试一个包含多个类为.list-item的列表项的页面：

javascript
describe('List items count test', () => {
  it('should have the correct number of .list-item elements', () => {
    // 访问你的页面
    cy.visit('your-page-url');
    
    // 获取所有的.list-item元素，并断言其长度
    cy.get('.list-item').its('length').should('eq', 5);
  });
});

在这个例子中，我们期望页面上有5个.list-item的元素。.its('length')会获取到.list-item的数量，并且.should('eq', 5)用于断言这个数量是否等于5。如果不等于5，测试会失败。

Found a solution, This works to check a count of items:

shell
cy.get('.datatable').find('tr').should('have.length', 4)

This does not work with the Cypress.$() method of notation.

Reference: https://docs.cypress.io/guides/references/assertions.html#Length

You can also get the length of a selection of items through its property, for example:

shell
cy.get('.datatable').find('tr').its('length').should('eq', 4)
cy.get('.datatable').find('tr').its('length').should('be.gte', 4)

In addition to should('have.length', 4)

I tested with Cypress version 3.1.0 and 3.2.0.

if you want more flexible and have a dynamic result use this.

shell
cy.get('.listings-grid')
  .find('.listing')
  .then(listing => {
    const listingCount = Cypress.$(listing).length;
    expect(listing).to.have.length(listingCount);
  });

One option is to use "have.length" ...

shell
cy.get('.datatable tr').should('have.length', 4)

...another option is to use should

shell
cy.get('.datatable tr').should(($tr) => {
    expect($tr).to.have.length(4)
})

...or then (synchronous queries)

shell
cy.get('.datatable').then(($table) => {
  // synchronously query to find length of elements
  expect($table.find('td').length).to.equal(4)
})

From the cypress API docs .should() section, using an arrow function:

shell
cy.get('.datatable').find('tr').should(($listOfElements) => {
   expect($listOfElements).to.have.length(4)
   // any other assertions, for example the below one
   // expect($listOfElements).to.have.any.keys('key1', 'key2')
})

This approach will allow you to use Chai BDD notation and assert more than one thing on your list of elements.