Why websockets?
There are already many servers written for the Pi utilizing HTTP protocols. However, websockets offer low-latency communication and tighter JSON-RPC structures (source). This protocol may be more complex to set up for the first time, but working with it is clean and simple.
This library does not use websocket wrappers like socket.io or fallback protocols like Flash. This is pure websocket. As such, it requires using a supported browser.