BDD / TDD assertion framework for node.js and the browser that can be paire...



Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework.

license:mit tag:? node:?
Selenium Test Status
downloads:? build:? coverage:? devDependencies:?
Join the Slack chat Join the Gitter chat OpenCollective Backers

For more information or to download plugins, view the documentation.

What is Chai?

Chai is an _assertion library_, similar to Node's built-in assert. It makes testing much easier by giving you lots of assertions you can run against your code.



chai is available on npm. To install it, type:

  1. ``` sh
  2. $ npm install --save-dev chai
  3. ```


You can also use it within the browser; install via npm and use the chai.js file found within the download. For example:

  1. ```html
  2. <script src="./node_modules/chai/chai.js"></script>
  3. ```


Import the library in your code, and then pick one of the styles you'd like to use - either assert, expect or should:

  1. ```js
  2. var chai = require('chai');  
  3. var assert = chai.assert;    // Using Assert style
  4. var expect = chai.expect;    // Using Expect style
  5. var should = chai.should();  // Using Should style
  6. ```

Pre-Native Modules Usage (_registers the chai testing style globally_)

  1. ```js
  2. require('chai/register-assert');  // Using Assert style
  3. require('chai/register-expect');  // Using Expect style
  4. require('chai/register-should');  // Using Should style
  5. ```

Pre-Native Modules Usage (_as local variables_)

  1. ```js
  2. const { assert } = require('chai');  // Using Assert style
  3. const { expect } = require('chai');  // Using Expect style
  4. const { should } = require('chai');  // Using Should style
  5. should();  // Modifies `Object.prototype`

  6. const { expect, use } = require('chai');  // Creates local variables `expect` and `use`; useful for plugin use
  7. ```

Native Modules Usage (_registers the chai testing style globally_)

  1. ```js
  2. import 'chai/register-assert';  // Using Assert style
  3. import 'chai/register-expect';  // Using Expect style
  4. import 'chai/register-should';  // Using Should style
  5. ```

Native Modules Usage (_local import only_)

  1. ```js
  2. import { assert } from 'chai';  // Using Assert style
  3. import { expect } from 'chai';  // Using Expect style
  4. import { should } from 'chai';  // Using Should style
  5. should();  // Modifies `Object.prototype`
  6. ```

Usage with Mocha

  1. ```bash
  2. mocha spec.js -r chai/register-assert  # Using Assert style
  3. mocha spec.js -r chai/register-expect  # Using Expect style
  4. mocha spec.js -r chai/register-should  # Using Should style
  5. ```


Chai offers a robust Plugin architecture for extending Chai's assertions and interfaces.

- Need a plugin? View the official plugin list.
- Want to build a plugin? Read the plugin api documentation.
- Have a plugin and want it listed? Simply add the following keywords to your package.json:
  -  chai-plugin
  -  browser if your plugin works in the browser as well as Node.js
  -  browser-only if your plugin does not work with Node.js

Related Projects

- chaijs / chai-docs: The website source code.
- chaijs / assertion-error: CustomError constructor thrown upon an assertion failing.
- chaijs / deep-eql: Improved deep equality testing for Node.js and the browser.
- chaijs / type-detect: Improved typeof detection for Node.js and the browser.
- chaijs / check-error: Error comparison and information related utility for Node.js and the browser.
- chaijs / loupe: Inspect utility for Node.js and browsers.
- chaijs / pathval: Object value retrieval given a string path.
- chaijs / get-func-name: Utility for getting a function's name for node and the browser.


Thank you very much for considering to contribute!

Please make sure you follow our Code Of Conduct and we also strongly recommend reading our Contributing Guide.

Here are a few issues other contributors frequently ran into when opening pull requests:

- Please do not commit changes to the chai.js build. We do it once per release.
- Before pushing your commits, please make sure you rebase them.


Please see the full
list of contributors.

Core Contributors

Feel free to reach out to any of the core contributors with your questions or
concerns. We will do our best to respond in a timely manner.
Jake Luer Veselin Todorov Keith Cirkel Lucas Fernandes da Costa Grant Snodgrass