Cypress: TypeScript vs JavaScript

Cypress is a popular end - to - end testing framework that simplifies the process of testing web applications. When using Cypress, developers have the option to write their test suites in either JavaScript or TypeScript. Both languages have their own characteristics, and understanding their differences can help you make an informed decision based on your project requirements. This blog post will explore the fundamental concepts, usage methods, common practices, and best practices of using Cypress with JavaScript and TypeScript.

Table of Contents

  1. Fundamental Concepts
  2. Usage Methods
  3. Common Practices
  4. Best Practices
  5. Conclusion
  6. References

Fundamental Concepts

JavaScript in Cypress

JavaScript is a dynamic, untyped language. It is one of the most widely used programming languages for web development. When using Cypress with JavaScript, you write test code in plain JavaScript. The test code can directly interact with the DOM elements of the web application under test. JavaScript is known for its flexibility and simplicity, allowing developers to quickly write and execute test cases without the need for strict type definitions.

Here is a basic example of a Cypress test written in JavaScript:

describe('My first JavaScript test', () => {
    it('Visits the app root url', () => {
        cy.visit('/')
        cy.contains('Welcome to my app')
    })
})

In this example, describe is used to group related tests, and it is used to define an individual test case. cy.visit is a Cypress command to visit a URL, and cy.contains checks if the page contains a specific text.

TypeScript in Cypress

TypeScript is a superset of JavaScript. It adds static typing to JavaScript, which means you can define types for variables, function parameters, and return values. In the context of Cypress, TypeScript can enhance the development experience by providing better code completion, early error detection, and more structured code.

Here is a similar Cypress test written in TypeScript:

describe('My first TypeScript test', () => {
    it('Visits the app root url', () => {
        cy.visit('/')
        cy.contains('Welcome to my app')
    })
})

Although the test logic is the same as the JavaScript example, TypeScript allows you to catch type - related errors during the compilation process. For example, if you try to pass an incorrect type to a Cypress command, TypeScript will flag it.

Usage Methods

Setting up a Cypress project with JavaScript

  1. Initialize a new project:
    • First, create a new directory for your project and navigate to it in the terminal. Then initialize a new npm project:
mkdir cypress-js-project
cd cypress-js-project
npm init -y
  1. Install Cypress:
npm install cypress --save-dev
  1. Open Cypress:
npx cypress open
  1. Create test files: Create a test file, for example, example.js in the cypress/integration directory. You can start writing Cypress tests in JavaScript in this file.

Setting up a Cypress project with TypeScript

  1. Initialize a new project and install Cypress: Follow the same steps as above to initialize a new npm project and install Cypress.
  2. Install TypeScript and related dependencies:
npm install typescript @types/cypress --save-dev
  1. Configure TypeScript: Create a tsconfig.json file in the root of your project with the following basic configuration:
{
    "compilerOptions": {
        "target": "es5",
        "lib": ["es5", "dom"],
        "types": ["cypress"]
    },
    "include": ["cypress/**/*.ts"]
}
  1. Create TypeScript test files: Create test files with the .ts extension in the cypress/integration directory. Cypress will automatically transpile the TypeScript code during the test execution.

Common Practices

JavaScript common practices

  • Modularize test code: Break down large test suites into smaller, more manageable functions. For example:
function visitAndCheckText(url, text) {
    cy.visit(url)
    cy.contains(text)
}

describe('Modularized JavaScript test', () => {
    it('Checks page content', () => {
        visitAndCheckText('/', 'Welcome to my app')
    })
})
  • Use custom commands: Cypress allows you to define custom commands in cypress/support/commands.js. For example:
Cypress.Commands.add('login', (username, password) => {
    cy.get('#username').type(username)
    cy.get('#password').type(password)
    cy.get('#login-button').click()
})

Then in your test:

describe('Login test', () => {
    it('Logs in successfully', () => {
        cy.login('user', 'pass')
    })
})

TypeScript common practices

  • Use type annotations: Leverage TypeScript’s type system to make your code more robust. For example, when defining a custom command:
Cypress.Commands.add('login', (username: string, password: string) => {
    cy.get('#username').type(username)
    cy.get('#password').type(password)
    cy.get('#login-button').click()
})
  • Interface definition for complex objects: If you are dealing with complex data structures in your tests, define interfaces. For example:
interface User {
    username: string;
    password: string;
}

describe('User login test', () => {
    it('Logs in with user object', () => {
        const user: User = { username: 'user', password: 'pass' };
        // Use the user object in the custom login command
        cy.login(user.username, user.password)
    })
})

Best Practices

JavaScript best practices

  • Avoid global variables: Global variables can lead to hard - to - debug issues, especially in a test environment where tests should be independent. Instead, pass data as parameters to functions.
  • Write descriptive test names: Use clear and descriptive names for test cases. For example, instead of it('test 1'), use it('Should display welcome message after login').

TypeScript best practices

  • Take advantage of type guards: Use type guards to narrow down the type of a variable in conditional statements. For example:
function checkValue(value: string | number) {
    if (typeof value ==='string') {
        // TypeScript now knows that value is a string
        console.log(value.length);
    }
}
  • Use enums for constants: When you have a set of related constants, use enums to make the code more readable and maintainable.
enum PageUrls {
    HOME = '/',
    ABOUT = '/about'
}

describe('Navigation test', () => {
    it('Visits home page', () => {
        cy.visit(PageUrls.HOME)
    })
})

Conclusion

Both JavaScript and TypeScript have their own advantages when used with Cypress. JavaScript is simple and flexible, making it easy to quickly write and execute tests. It is suitable for small - scale projects or when you need to iterate quickly. On the other hand, TypeScript provides static typing, which can catch errors early in the development process, making the code more robust and maintainable, especially in large - scale projects.

Ultimately, the choice between Cypress with JavaScript and Cypress with TypeScript depends on the nature and size of your project, the development team’s familiarity with the languages, and the need for code safety and maintainability.

References