JavaScript WebSockets with UDP?

The WebSockets protocol is over TCP only as currently defined.

You could do UDP with Flash if you are willing to use a RTMFP (Real Time Messaging Flow Protocol) server.

It sounds like what you're waiting for is WebRTC which is working it's way through the standards process. WebSockets, as other people have pointed out, run over TCP as a result of initiating with an HTTP Upgrade.

Sounds like the question is meant for client-side UDP, but since I ended up here...

You can do UDP in JavaScript on the server using the node.js dgram package.

No, it's not possible to have UDP communication within JavaScript. Sorry.