At the time of writing this book, the WebRTC specifications were still not finalized. The overall idea of what WebRTC does and how WebRTC works has been finalized. It's just that the APIs are still under development.
For example, WebRTC has introduced an alternative to the navigator.getUserMedia() method, that is, the navigator.mediaDevices.getUserMedia() method. At the time of writing this book, navigator.mediaDevices.getUserMedia() is not supported in any browsers. The difference between them is that the navigator.mediaDevices.getUserMedia() method is based on the promise pattern, whereas navigator.getUserMedia() is based on the callback pattern. At present, there is no plan to get rid of navigator.getUserMedia() due to the backward compatibility reason, but in future, navigator.getUserMedia() may be removed as WebRTC wants to implement all APIs using the promise pattern, therefore, it's difficult to maintain multiple APIs that do the same thing. Similarly, navigator.mediaDevices...