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Vitest, the modern Vite-native test runner, has introduced Vitest Browser Mode, offering developers an alternative to traditional DOM simulation libraries like JSDOM. The addition of browser mode to Vitest allows tests to run in an actual browser context, offering more realistic and reliable testing behavior for UI applications built with React, Vue, or Svelte.

Vitest Browser Mode is currently experimental.

Vitest Browser Mode was introduced to help improve testing with more accurate and reliable test results, it does this by running tests in a real browser context using Playwright or WebDriverIO. This mode allows for realistic browser rendering and interaction.

Historically, JSDOM has been the default simulated environment for running front-end tests in Node.js. It simulates a browser DOM inside Node, making it a convenient and fast option for unit testing. However, due to the fact that JSDOM isn’t a real browser, its implementation can sometimes fall short for advanced use cases, such as layout calculations, CSS behavior, or APIs not yet supported in JSDOM. Vitest aims to replace JSDOM environments with an easy migration path.

React Testing Library, a lightweight library for testing React components, is built on top of the DOM Testing Library, which provides utilities to interact with the DOM. It has long relied on JSDOM for simulating DOM interaction. With the introduction of Vitest Browser Mode, it is possible to migrate away from React Testing Library as a number of the APIs have been natively rewritten in the same familiar pattern of React Testing Library. Kent C. Dodds, the author of React Testing Library, says he has never been so happy to see people uninstalling React Testing Library in favor of the native implementation.

Vitest also provides support for other frameworks, such as Vue and Svelte. There is also a community package available for Lit. It supports multiple different browser environments depending on which platform you use, if you opt for WebDriverIO, it supports testing in four different browsers, Firefox, Chrome, Edge and Safari. Playwright supports Firefox, Webkit and Chromium.

There are some drawbacks to using Vitest Browser Mode, as outlined in their documentation, such as it being in experimental mode and therefore still early in its development. It can also have longer initialization times compared to other testing patterns.

Vite is an open-source, platform-agnostic build tool named after the French word for ‘quick’. It was written by Evan You, the creator of VueJS. Vitest is a next generation Vite-native framework that reuses Vite’s config and plugins; it supports ESM, TypeScript and JSX out of the box.

Full documentation for Browser Mode is available on the Vitest website including setup guides and examples.