In the latest release of Cylon.js, we removed the API from the core in favor of a separtate plug-in system for API modules. We currently have two different API plugins to choose from, cylon-api-http and the recently added cylon-api-socketio.
The newest API plugin, cylon-api-socketio, makes it easy to command or retrieve data from a Cylon.js robot simply by using a socket.io client such as a browser-based application. You could easily add sensors to your robot and monitor them in real-time, fly a drone from your browser, or connect to one robot and then trigger functionality in another robot, all based on real-time sensor data! Checkout all of the cool new features in our in-depth blog post on the socket.io API plugin here.