Custom Queries

Cypress comes with its own API for creating custom queries. The built in Cypress queries use the very same API that's defined below.

If your method needs to be asynchronous, or it shouldn't be called more than once, consider writing a custom command instead.

A great place to define queries is in your cypress/support/commands.js file, since it is loaded before any test files are evaluated via an import statement in the supportFile.

Queries follow three main rules.

Queries are synchronous. They do not return or await promises.
Queries are retrieable. Once you return the inner function, Cypress takes control, handling retries on your behalf.
Queries are idempotent. Once you return the inner function, Cypress will invoke it repeatedly.

With these rules, queries are simple to write and extremely powerful. They are the building blocks on which Cypress' API is built.

Syntax

Cypress.Commands.addQuery(name, callbackFn)

Usage

Correct Usage

Cypress.Commands.addQuery('getById', function (id) {
  return (subject) => newSubject
})

Arguments

name (String)

The name of the query you're adding.

callbackFn (Function)

Pass a function that receives the arguments passed to the query.

This outer function is invoked once. It should return a function that takes a subject and returns a new subject; this inner function will be called multple times.

Examples

`.focused()`

The callback function can be thought of as two separate parts. The outer function, which is invoked once, where you perform setup and state management, and the query function, which is called repeatedly.

Let's look at an example. This is actual Cypress code - how .focused() is implemented internally. The only thing omitted here for simplicity is the typescript definitions.

Commands.addQuery('focused', function focused(options = {}) {
  const log = options.log !== false && Cypress.log({ timeout: options.timeout })

  this.set('timeout', options.timeout)

  return () => {
    let $el = cy.getFocused()

    log &&
      cy.state('current') === this &&
      log.set({
        $el,
        consoleProps: () => {
          return {
            Yielded: $el?.length ? $dom.getElements($el) : '--nothing--',
            Elements: $el != null ? $el.length : 0,
          }
        },
      })

    if (!$el) {
      $el = $dom.wrap(null)
      $el.selector = 'focused'
    }

    return $el
  }
})

Let's go over this piece by piece.

The outer function

The outer function is called once each time test uses the query. It performs setup and state management:

function focused(options = {}) {
  const log = options.log !== false && Cypress.log({ timeout: options.timeout })

  this.set('timeout', options.timeout)

  return () => {} // Inner function
}

Piece by piece, then.

function focused(options = {}) {}

Cypress passes the outer function whatever arguments the user calls it with; no processing or validation is done on the user's arguments. In our case, .focused() accepts one optional argument, options.

If you wanted to validate the incoming arguments, you might write something like:

if (options === null || !_.isPlainObject(options)) {
  const err = `cy.root() requires an \`options\` object. You passed in: \`{options}\``
  throw new TypeError(err)
}

This is a general pattern: when something goes wrong, queries just throw an error. Cypress will handle displaying this in the Command Log nicely.

const log = options.log !== false && Cypress.log({ timeout: options.timeout })

If the user has not set { log: false }, we create a new Cypress.log() instance. See Cypress.log() for more information.

This is setup code - we only want it to run once, creating the log message when Cypress first begins executing this query. We hold onto a reference to Log instance - we'll update it later with additional details.

this.set('timeout', options.timeout)

When defining focused(), it's important to note that we used function, rather than an arrow function. This gives us access to this, where we can set the timeout. If you don't call this.set('timeout'), or call it with null or undefined, your query will use the default timeout.

  return () => { ... }

The outer function's return value is the inner function.

The inner function

The inner function is called any number of times. It's first invoked repeatedly until it passes or the query times out; it can then be invoked again later to determine the subject of future commands, or when the user retrieves an alias.

The inner function is called with one argument: the previous subject. Cypress performs no validation on this - it could be any type, including null or undefined.

.focused() ignores any previous subject, but many queries do not - for example, .contains() accepts only certain types of subjects. You can use Cypress' builtin ensures functions, as .contains() does: cy.ensureSubjectByType(subject, ['optional', 'element', 'window', 'document'], this)

or you can perform your own validation and simply throw an error: if (!_.isString(subject)) { throw new Error('MyCustomCommand only accepts strings as a subject!') }

If the inner function throws an error, Cypress will retry it after a short delay until it either passes or the query times out. This is the core of Cypress' retry-ability, and the guarantees it provides that your tests interact with the page as a user would.

Looking back to our .focused() example:

return () => {
  let $el = cy.getFocused()

  log &&
    cy.state('current') === this &&
    log.set({
      $el,
      consoleProps: () => {
        return {
          Yielded: $el?.length ? $dom.getElements($el) : '--nothing--',
          Elements: $el != null ? $el.length : 0,
        }
      },
    })

  if (!$el) {
    $el = $dom.wrap(null)
    $el.selector = 'focused'
  }

  return $el
}

Piece by piece again:

let $el = cy.getFocused()

This is the 'business end' of .focused() - finding the element on the page that's currently focused.

    log && cy.state('current') === this && log.set({...})

If log is defined (ie, the user did not pass in { log: false }), and this query is the current command, we update the log message with new information, such as $el (the subject we're about to yield from this query), and the consoleProps, a function that returns console output for the user.

if (!$el) {
  $el = $dom.wrap(null)
  $el.selector = 'focused'
}

If there's no focused element on the page, we create an empty jquery object.

return $el

The return value of the inner function becomes the new subject for the next command.

With this return value in hand, Cypress verifies any upcoming assertions, such as user's .should() commands, or if there are none, the default implicit assertions that the subject should exist.

Using existing queries

Many custom queries are wrappers around other, already implemented queries - most commonly .get().

This is quite simple:

Cypress.Commands.addQuery('getFirstButton', function getFirstButton(options) {
  const getFn = cy.now('get', 'button:first', options)

  return (subject) => {
    console.log('The subject we received was:', subject)

    const btn = getFn(subject)

    console.log('.get returned this element:', btn)

    return btn
  }
})

Calling cy.now() on a query calls the outer function of that query, and returns the inner function. In our case, we call get with button:first and pass through whatever options the user provided us.

In our own inner function, we can then call getFn, and do whatever we want with the return value.

Validations

As noted in the examples above, Cypress performs very little validation around queries - it is the repsonsibility of each implementation to ensure that its arguments and subject are of the correct type.

Cypress has several builtin 'ensures' which can be helpful in this regard:

cy.ensureSubjectByType(subject, types, this): Accepts an array with any of the strings optional, element, document, or window. ensureSubjectByType is how prevSubject validation is implemented for commmands.
cy.ensureElement(subject, queryName): Ensure that the passed in subject is one or more DOM elements.
cy.ensureWindow(subject): Ensure that the passed in subject is a document.
cy.ensureDocument(subject): Ensure that the passed in subject is a window.
cy.ensureAttached(subject, queryName): Ensure that DOM element(s) are attached to the page.
cy.ensureNotDisabled(subject): Ensure that form elements aren't disabled.
cy.ensureVisibility(subject): Ensure that a DOM element is visible on the page.

There's nothing special about these functions - they simply validate their argument and throw an error if the check fails. You can throw errors of any type at any time inside your queries - Cypress will catch and handle it appropriately.

Notes

Best Practices

1. Don't make everything a custom query

Custom queries work well when you're needing to describe behavior that's desirable across all of your tests. Examples would be cy.findBreadcrumbs() or cy.getLoginForm(). These are specific to your application and can be used everywhere.

However, this pattern can be used and abused. Let's not forget - writing Cypress tests is JavaScript, and it's often more efficient to write a function for repeatable behavior than it is to implement a custom query.

2. Don't overcomplicate things

Every custom query you write is generally an abstraction for locating elements on the page. That means you and your team members exert much more mental effort to understand what your custom command does.

There's no reason to add this level of complexity when the builtin queries are already quite expressive and powerful.

Don't do things like:

cy.getButton()
.getFirstTableRow()

Both of these are wrapping cy.get(selector). It's completely unnecessary. Just call .get('button') or .get('tr:first').

Testing in Cypress is all about readability and simplicity. You don't have to do that much actual programming to get a lot done. You also don't need to worry about keeping your code as DRY as possible. Test code serves a different purpose than app code. Understandability and debuggability should be prioritized above all else.

Try not to overcomplicate things and create too many abstractions.

History

Version	Changes
12.0.0	`addQuery` API added