Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework.
For more information or to download plugins, view the [documentation](http://chaijs.com).
## 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.
## Installation
### Node.js
`chai` is available on [npm](http://npmjs.org). To install it, type:
$ npm install chai
### Browsers
You can also use it within the browser; install via npm and use the `chai.js` file found within the download. For example:
```html
```
## Usage
Import the library in your code, and then pick one of the styles you'd like to use - either `assert`, `expect` or `should`:
```js
var chai = require('chai');
var assert = chai.assert; // Using Assert style
var expect = chai.expect; // Using Expect style
var should = chai.should(); // Using Should style
```
### Pre-Native Modules Usage (_registers the chai testing style globally_)
```js
require('chai/register-assert'); // Using Assert style
require('chai/register-expect'); // Using Expect style
require('chai/register-should'); // Using Should style
```
### Pre-Native Modules Usage (_as local variables_)
```js
const { assert } = require('chai'); // Using Assert style
const { expect } = require('chai'); // Using Expect style
const { should } = require('chai'); // Using Should style
should(); // Modifies `Object.prototype`
const { expect, use } = require('chai'); // Creates local variables `expect` and `use`; useful for plugin use
```
### Native Modules Usage (_registers the chai testing style globally_)
```js
import 'chai/register-assert'; // Using Assert style
import 'chai/register-expect'; // Using Expect style
import 'chai/register-should'; // Using Should style
```
### Native Modules Usage (_local import only_)
```js
import { assert } from 'chai'; // Using Assert style
import { expect } from 'chai'; // Using Expect style
import { should } from 'chai'; // Using Should style
should(); // Modifies `Object.prototype`
```
### Usage with Mocha
```bash
mocha spec.js -r chai/register-assert # Using Assert style
mocha spec.js -r chai/register-expect # Using Expect style
mocha spec.js -r chai/register-should # Using Should style
```
[Read more about these styles in our docs](http://chaijs.com/guide/styles/).
## Plugins
Chai offers a robust Plugin architecture for extending Chai's assertions and interfaces.
- Need a plugin? View the [official plugin list](http://chaijs.com/plugins).
- Want to build a plugin? Read the [plugin api documentation](http://chaijs.com/guide/plugins/).
- 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](https://github.com/chaijs/chai-docs): The chaijs.com website source code.
- [chaijs / assertion-error](https://github.com/chaijs/assertion-error): Custom `Error` constructor thrown upon an assertion failing.
- [chaijs / deep-eql](https://github.com/chaijs/deep-eql): Improved deep equality testing for Node.js and the browser.
- [chaijs / type-detect](https://github.com/chaijs/type-detect): Improved typeof detection for Node.js and the browser.
- [chaijs / check-error](https://github.com/chaijs/check-error): Error comparison and information related utility for Node.js and the browser.
- [chaijs / loupe](https://github.com/chaijs/loupe): Inspect utility for Node.js and browsers.
- [chaijs / pathval](https://github.com/chaijs/pathval): Object value retrieval given a string path.
- [chaijs / get-func-name](https://github.com/chaijs/get-func-name): Utility for getting a function's name for node and the browser.
### Contributing
Thank you very much for considering to contribute!
Please make sure you follow our [Code Of Conduct](https://github.com/chaijs/chai/blob/master/CODE_OF_CONDUCT.md) and we also strongly recommend reading our [Contributing Guide](https://github.com/chaijs/chai/blob/master/CONTRIBUTING.md).
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](https://github.com/chaijs/chai/blob/master/CONTRIBUTING.md#pull-requests) them.
### Contributors
Please see the full
[Contributors Graph](https://github.com/chaijs/chai/graphs/contributors) for our
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.
[](https://github.com/logicalparadox)
[](https://github.com/vesln)
[](https://github.com/keithamus)
[](https://github.com/lucasfcosta)
[](https://github.com/meeber)
