Node
Chai is available for both node.js and the browser using any test framework you like.
Node.js
Package is available through npm:
npm install chai
Recommend adding it to package.json devDependancies.
Browser
Include the chai browser build in your testing suite.
<script src="chai.js" type="text/javascript"></script>
Currently supports all modern browsers: IE 9+, Chrome 7+, FireFox 4+, Safari 5+.
Want to know if your browser is compatible? Run the online test suite.
The latest tagged version will also be available for hot-linking at http://chaijs.com/chai.js.