TypeScript support for custom commands in Cypress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of adding TypeScript support for custom commands in Cypress?

It helps Cypress recognize the new commands with proper types, enabling code completion and type checking, which reduces errors and improves developer experience.

beginner

Where do you declare the types for your custom Cypress commands?

You declare them in a TypeScript declaration file, usually named cypress/support/index.d.ts or cypress/support/commands.d.ts, by extending the Cypress.Chainable interface.

intermediate

How do you extend Cypress commands with TypeScript to add a custom command named login?

You add a declaration like declare namespace Cypress { interface Chainable { login(email: string, password: string): Chainable<void>; } } in a declaration file, then implement Cypress.Commands.add('login', (email, password) => { ... }) in your commands file.

intermediate

Why is it important to declare custom Cypress command types in the support declaration file?

Declaring them there ensures TypeScript automatically knows about the custom commands' types when writing tests, so you get autocomplete and error checking for those commands.

beginner

What happens if you use a custom Cypress command without adding TypeScript support?

TypeScript will not recognize the command, causing errors or missing autocomplete, which can lead to mistakes or slower development.

Where do you extend the Cypress command types for custom commands in TypeScript?

A In a Cypress configuration JSON file

B In a TypeScript declaration file (<code>.d.ts</code>)

C In a <code>.ts</code> test file

D In the package.json file

Custom command types are declared in a TypeScript declaration file to extend Cypress.Chainable interface.

What interface do you extend to add custom commands in Cypress TypeScript support?

A Cypress.Chainable

B Cypress.CommandsInterface

C Cypress.CustomCommands

D Cypress.Commands

You extend the Cypress.Chainable interface to add custom command types.

Which of the following is the correct way to add a custom command implementation in Cypress?

A Cypress.Commands.add('myCommand', () => {})

B Cypress.Commands.create('myCommand', () => {})

C Cypress.addCommand('myCommand', () => {})

D Cypress.createCommand('myCommand', () => {})

The correct method to add a custom command is Cypress.Commands.add.

What benefit does TypeScript support for custom commands provide?

A Faster test execution

B Better UI design

C Type checking and autocomplete for custom commands

D Automatic test retries

TypeScript support provides type checking and autocomplete, improving code quality and developer experience.

If you forget to declare your custom command types, what will happen in your TypeScript Cypress tests?

A Tests will run faster

B Tests will fail to run

C Nothing, it works fine

D You will get type errors or no autocomplete for the custom commands

Without declaration, TypeScript does not recognize the custom commands, causing errors or missing autocomplete.

Explain how to add TypeScript support for a custom Cypress command named 'login'.

Think about declaration files and interface extension.

Why is it important to extend Cypress.Chainable interface when adding custom commands in TypeScript?

Consider how TypeScript understands new methods.

Practice

1. What is the main benefit of adding TypeScript support for custom commands in Cypress?

easy

A. It makes tests run faster by optimizing command execution.

B. It provides type checking and better editor autocomplete for custom commands.

C. It automatically generates test reports for custom commands.

D. It allows running tests on multiple browsers simultaneously.

Solution

1. Step 1: Understand TypeScript role in Cypress

   TypeScript adds static type checking and editor support to catch errors early.

2. Step 2: Identify benefit for custom commands

   Typing custom commands improves autocomplete and prevents mistakes when using them.

3. Final Answer:

   It provides type checking and better editor autocomplete for custom commands. -> Option B

4. Quick Check:

   TypeScript support = type checking + autocomplete [OK]

Hint: TypeScript helps catch errors before running tests [OK]

Common Mistakes:

• Confusing TypeScript support with test speed improvements
• Thinking it auto-generates reports
• Believing it enables multi-browser runs

2. Which is the correct way to declare a custom command with TypeScript support in Cypress?

easy

A. namespace Cypress { interface myCommand { Chainable(): void } }

B. interface Cypress { Chainable { myCommand(): void } }

C. declare interface Cypress { myCommand(): void }

D. declare namespace Cypress { interface Chainable { myCommand(): Chainable<void> } }

Solution

1. Step 1: Recall TypeScript declaration syntax for Cypress commands

   Custom commands are declared inside the Cypress namespace extending Chainable interface.

2. Step 2: Match correct syntax

   declare namespace Cypress { interface Chainable { myCommand(): Chainable<void> } } correctly uses 'declare namespace Cypress' and extends 'Chainable' with 'myCommand'.

3. Final Answer:

   declare namespace Cypress { interface Chainable { myCommand(): Chainable<void> } } -> Option D

4. Quick Check:

   Namespace + Chainable interface = correct declaration [OK]

Hint: Custom commands extend Cypress.Chainable interface inside namespace [OK]

Common Mistakes:

• Missing 'declare' keyword
• Incorrect interface or namespace nesting
• Placing method outside Chainable interface

3. Given this TypeScript declaration for a custom command:

declare namespace Cypress {
  interface Chainable {
    login(email: string, password: string): Chainable<void>
  }
}

What is the correct way to use this login command in a test?

medium

A. cy.login(['[e-mail]', 'pass123'])

B. cy.login(email: '[e-mail]', password: 'pass123')

C. cy.login('[e-mail]', 'pass123')

D. cy.login()

Solution

1. Step 1: Understand method signature

   The login command takes two string arguments: email and password.

2. Step 2: Match correct usage syntax

   cy.login('[e-mail]', 'pass123') calls login with two string arguments in order, matching the declaration.

3. Final Answer:

   cy.login('[e-mail]', 'pass123') -> Option C

4. Quick Check:

   Method call with two string args = correct usage [OK]

Hint: Pass arguments as ordered parameters, not as object or array [OK]

Common Mistakes:

• Using named parameters syntax (not valid in JS calls)
• Passing arguments as array instead of separate params
• Calling without required arguments

4. You wrote this custom command declaration:

declare namespace Cypress {
  interface Chainable {
    clickButton(): void
  }
}

But when you use cy.clickButton() in your test, TypeScript shows an error. What is the problem?

medium

A. The return type should be Chainable<void>, not void.

B. The method name cannot be clickButton.

C. Custom commands must be declared outside the Cypress namespace.

D. You forgot to import Cypress in the test file.

Solution

1. Step 1: Check return type for custom commands

   Custom commands should return Chainable<T> to allow chaining in Cypress.

2. Step 2: Identify mismatch causing TypeScript error

   Returning void breaks chaining and causes TypeScript to complain.

3. Final Answer:

   The return type should be Chainable<void>, not void. -> Option A

4. Quick Check:

   Custom commands must return Chainable for chaining [OK]

Hint: Custom commands return Chainable, not void [OK]

Common Mistakes:

• Using void return type instead of Chainable
• Declaring commands outside Cypress namespace
• Assuming method names are restricted

5. You want to create a custom command fillForm that accepts an object with optional name and email fields. How should you declare it in TypeScript to support chaining and optional properties?

hard

A. declare namespace Cypress { interface Chainable { fillForm(data: { name?: string; email?: string }): Chainable<void> } }

B. declare namespace Cypress { interface Chainable { fillForm(data: { name: string; email: string }): void } }

C. declare namespace Cypress { interface Chainable { fillForm(data?: { name: string; email: string }): Chainable<void> } }

D. declare namespace Cypress { interface Chainable { fillForm(data: { name: string; email?: string }): Chainable<string> } }

Solution

1. Step 1: Define optional properties correctly

   Use question marks (?) to mark properties as optional in the data object.

2. Step 2: Ensure return type supports chaining

   Return type must be Chainable<void> to allow chaining in Cypress tests.

3. Final Answer:

   declare namespace Cypress { interface Chainable { fillForm(data: { name?: string; email?: string }): Chainable<void> } } -> Option A

4. Quick Check:

   Optional props + Chainable return = correct declaration [OK]

Hint: Use '?' for optional props and Chainable<void> return [OK]

Common Mistakes:

• Forgetting '?' for optional properties
• Using void return type instead of Chainable
• Returning wrong Chainable generic type