Variables and Aliases

Return Values

New users to Cypress may initially find it challenging to work with the asynchronous nature of our APIs.

Asynchronous APIs are here to stay in JavaScript. They are found everywhere in modern code. In fact, most new browser APIs are asynchronous and many core Node modules are asynchronous as well.

The patterns we'll explore below are useful in and outside of Cypress.

The first and most important concept you should recognize is...

// this won't work the way you think it does
const button = cy.get('button')
const form = cy.get('form')

button.click()

Closures

To access what each Cypress command yields you use .then().

cy.get('button').then(($btn) => {
  // $btn is the object that the previous
  // command yielded us
})

If you're familiar with native Promises the Cypress .then() works the same way. You can continue to nest more Cypress commands inside of the .then().

Each nested command has access to the work done in previous commands. This ends up reading very nicely.

cy.get('button').then(($btn) => {

  // store the button's text
  const txt = $btn.text()

  // submit a form
  cy.get('form').submit()

  // compare the two buttons' text
  // and make sure they are different
  cy.get('button').should(($btn2) => {
    expect($btn2.text()).not.to.eq(txt)
  })
})

// these commands run after all of the
// other previous commands have finished
cy.get(...).find(...).should(...)

The commands outside of the .then() will not run until all of the nested commands finish.

Debugging

Using .then() functions is an excellent opportunity to use debugger. This can help you understand the order in which commands are run. This also enables you to inspect the objects that Cypress yields you in each command.

cy.get('button').then(($btn) => {
  // inspect $btn <object>
  debugger

  cy.get('#countries')
    .select('USA')
    .then(($select) => {
      // inspect $select <object>
      debugger

      cy.url().should((url) => {
        // inspect the url <string>
        debugger

        $btn // is still available
        $select // is still available too
      })
    })
})

Variables

Typically in Cypress you hardly need to ever use const, let, or var. When using closures you'll always have access to the objects that were yielded to you without assigning them.

The one exception to this rule is when you are dealing with mutable objects (that change state). When things change state you often want to compare an object's previous value to the next value.

Here's a great use case for a const.

<button>increment</button>

you clicked button <span id="num">0</span> times
// app code
let count = 0

$('button').on('click', () => {
  $('#num').text((count += 1))
})
// cypress test code
cy.get('#num').then(($span) => {
  // capture what num is right now
  const num1 = parseFloat($span.text())

  cy.get('button')
    .click()
    .then(() => {
      // now capture it again
      const num2 = parseFloat($span.text())

      // make sure it's what we expected
      expect(num2).to.eq(num1 + 1)
    })
})

The reason for using const is because the $span object is mutable. Whenever you have mutable objects and you're trying to compare them, you'll need to store their values. Using const is a perfect way to do that.

Aliases

Using .then() callback functions to access the previous command values is great—but what happens when you're running code in hooks like before or beforeEach?

beforeEach(() => {
  cy.button().then(($btn) => {
    const text = $btn.text()
  })
})

it('does not have access to text', () => {
  // how do we get access to text ?!?!
})

How will we get access to text?

We could make our code do some ugly backflips using let to get access to it.

describe('a suite', () => {
  // this creates a closure around
  // 'text' so we can access it
  let text

  beforeEach(() => {
    cy.button().then(($btn) => {
      // redefine text reference
      text = $btn.text()
    })
  })

  it('does have access to text', () => {
    // now text is available to us
    // but this is not a great solution :(
    text
  })
})

Fortunately, you don't have to make your code do backflips. With Cypress, we can better handle these situations.

Sharing Context

Sharing context is the simplest way to use aliases.

To alias something you'd like to share use the .as() command.

Let's look at our previous example with aliases.

beforeEach(() => {
  // alias the $btn.text() as 'text'
  cy.get('button').invoke('text').as('text')
})

it('has access to text', function () {
  this.text // is now available
})

Under the hood, aliasing basic objects and primitives utilizes Mocha's shared context object: that is, aliases are available as this.*.

Mocha automatically shares contexts for us across all applicable hooks for each test. Additionally these aliases and properties are automatically cleaned up after each test.

describe('parent', () => {
  beforeEach(() => {
    cy.wrap('one').as('a')
  })

  context('child', () => {
    beforeEach(() => {
      cy.wrap('two').as('b')
    })

    describe('grandchild', () => {
      beforeEach(() => {
        cy.wrap('three').as('c')
      })

      it('can access all aliases as properties', function () {
        expect(this.a).to.eq('one') // true
        expect(this.b).to.eq('two') // true
        expect(this.c).to.eq('three') // true
      })
    })
  })
})

Accessing Fixtures:

The most common use case for sharing context is when dealing with cy.fixture().

Often times you may load a fixture in a beforeEach hook but want to utilize the values in your tests.

beforeEach(() => {
  // alias the users fixtures
  cy.fixture('users.json').as('users')
})

it('utilize users in some way', function () {
  // access the users property
  const user = this.users[0]

  // make sure the header contains the first
  // user's name
  cy.get('header').should('contain', user.name)
})
it('is not using aliases correctly', function () {
  cy.fixture('users.json').as('users')

  // nope this won't work
  //
  // this.users is not defined
  // because the 'as' command has only
  // been enqueued - it has not run yet
  const user = this.users[0]
})

The same principles we introduced many times before apply to this situation. If you want to access what a command yields you have to do it in a closure using a .then().

// yup all good
cy.fixture('users.json').then((users) => {
  // now we can avoid the alias altogether
  // and use a callback function
  const user = users[0]

  // passes
  cy.get('header').should('contain', user.name)
})

Avoiding the use of this

Instead of using the this.* syntax, there is another way to access aliases.

The cy.get() command is capable of accessing aliases with a special syntax using the @ character:

beforeEach(() => {
  // alias the users fixtures
  cy.fixture('users.json').as('users')
})

it('utilize users in some way', function () {
  // use the special '@' syntax to access aliases
  // which avoids the use of 'this'
  cy.get('@users').then((users) => {
    // access the users argument
    const user = users[0]

    // make sure the header contains the first
    // user's name
    cy.get('header').should('contain', user.name)
  })
})

By using cy.get() we avoid the use of this.

Keep in mind that there are use cases for both approaches because they have different ergonomics.

When using this.users we have access to it synchronously, whereas when using cy.get('@users') it becomes an asynchronous command.

You can think of the cy.get('@users') as doing the same thing as cy.wrap(this.users).

Elements

Aliases have other special characteristics when being used with DOM elements.

After you alias DOM elements, you can then later access them for reuse.

// alias all of the tr's found in the table as 'rows'
cy.get('table').find('tr').as('rows')

Internally, Cypress has made a reference to the <tr> collection returned as the alias "rows". To reference these same "rows" later, you can use the cy.get() command.

// Cypress returns the reference to the <tr>'s
// which allows us to continue to chain commands
// finding the 1st row.
cy.get('@rows').first().click()

Because we've used the @ character in cy.get(), instead of querying the DOM for elements, cy.get() looks for an existing alias called rows and returns the reference (if it finds it).

Stale Elements:

In many single-page JavaScript applications the DOM re-renders parts of the application constantly. If you alias DOM elements that have been removed from the DOM by the time you call cy.get() with the alias, Cypress automatically re-queries the DOM to find these elements again.

<ul id="todos">
  <li>
    Walk the dog
    <button class="edit">edit</button>
  </li>
  <li>
    Feed the cat
    <button class="edit">edit</button>
  </li>
</ul>

Let's imagine when we click the .edit button that our <li> is re-rendered in the DOM. Instead of displaying the edit button it instead displays an <input /> text field allowing you to edit the todo. The previous <li> has been completely removed from the DOM and a new <li> is rendered in its place.

cy.get('#todos li').first().as('firstTodo')
cy.get('@firstTodo').find('.edit').click()
cy.get('@firstTodo')
  .should('have.class', 'editing')
  .find('input')
  .type('Clean the kitchen')

When we reference @firstTodo, Cypress checks to see if all of the elements it is referencing are still in the DOM. If they are, it returns those existing elements. If they aren't, Cypress replays the commands leading up to the alias definition.

In our case it would re-issue the commands: cy.get('#todos li').first(). Everything works because the new <li> is found.

Routes

Aliases can also be used with routes. Aliasing your routes enables you to:

  • ensure your application makes the intended requests
  • wait for your server to send the response
  • access the actual request object for assertions
Alias commands

Here's an example of aliasing a route and waiting on it to complete.

cy.intercept('POST', '/users', { id: 123 }).as('postUser')

cy.get('form').submit()

cy.wait('@postUser').then(({ request }) => {
  expect(request.body).to.have.property('name', 'Brian')
})

cy.contains('Successfully created user: Brian')

Requests

Aliases can also be used with requests.

Here's an example of aliasing a request and accessing its properties later.

cy.request('https://jsonplaceholder.cypress.io/comments').as('comments')

// other test code here

cy.get('@comments').should((response) => {
  if (response.status === 200) {
      expect(response).to.have.property('duration')
    } else {
      // whatever you want to check here
    }
  })
})

Aliases are reset before each test

Note: all aliases are reset before each test. A common user mistake is to create aliases using the before hook. Such aliases work in the first test only!

// 🚨 THIS EXAMPLE DOES NOT WORK
before(() => {
  // notice this alias is created just once using "before" hook
  cy.wrap('some value').as('exampleValue')
})

it('works in the first test', () => {
  cy.get('@exampleValue').should('equal', 'some value')
})

// NOTE the second test is failing because the alias is reset
it('does not exist in the second test', () => {
  // there is not alias because it is created once before
  // the first test, and is reset before the second test
  cy.get('@exampleValue').should('equal', 'some value')
})

The solution is to create the aliases before each test using the beforeEach hook

// ✅ THE CORRECT EXAMPLE
beforeEach(() => {
  // we will create a new alias before each test
  cy.wrap('some value').as('exampleValue')
})

it('works in the first test', () => {
  cy.get('@exampleValue').should('equal', 'some value')
})

it('works in the second test', () => {
  cy.get('@exampleValue').should('equal', 'some value')
})

See also