rest.js is a JavaScript HTTP client library that allows developers to make RESTful HTTP requests from both browsers and Node.js environments. It provides a modular approach where you can configure clients with only the features you need and compose them using interceptors for authentication, error handling, MIME type conversion, and other cross-cutting concerns. The library is designed for developers building web applications that need to consume REST APIs, with support for advanced features like hypermedia (HATEOAS) and URI template expansion.