Mocha

What Mocha is

Mocha is a free, open-source JavaScript test framework that runs in Node.js and browsers. Tests run serially by default, and Mocha maps uncaught exceptions to the relevant test cases. For asynchronous tests, developers can use callbacks or return promises. Parallel execution is available in Node.js, but not in browsers. The command-line interface defaults to the BDD interface and spec reporter; browser runs default to the HTML reporter. Reporters can be configured, and the CLI's --ui option selects an interface. Installation as a development dependency is documented for npm, pnpm and yarn. Mocha 12 requires Node.js ^20.19.0 or >=22.12.0. Browser builds document support for evergreen Chrome, Edge, Firefox and Safari. Mocha supports JavaScript and TypeScript and parameterized cases, but has no built-in mocks. Editor-related packages are listed for TextMate, JetBrains IDEs, Wallaby.js, Emacs and VS Code. The project points users to its Discord and documentation explainers for more information. Its security guidance says it runs in development and executes developer-provided code.

Who it suits

Mocha suits developers writing JavaScript or TypeScript tests for Node.js or browsers. It may also fit projects that need asynchronous or parameterized tests and configurable interfaces or reporters.

Limits

Mocha 12 requires Node.js ^20.19.0 or >=22.12.0. Parallel execution is limited to Node.js; browsers do not support it.

Getting started

1. Open the Mocha website and getting-started guide.
2. Install Mocha as a development dependency using npm, pnpm, or yarn.
3. Use a supported Node.js version for Mocha 12, or use a documented evergreen browser build.
4. Choose an interface and reporter that suit your test run.

Verdict

Mocha provides a free testing framework for Node.js and browser projects, with asynchronous and parallel execution options. Check its runtime requirements and browser parallel-mode limitation before adopting it.