I'm using websockets (node.js with ws.js) to receive realtime messages from online clients. How can I access these incoming messages on my visualization sketch (processing or processing.js) that runs on my server side?
Not entirely sure what you mean here - Processing can run anywhere, as a standalone application (compiled as java), Processing.js is what you use if you want to run a sketch on the web (compiled as JavaScript). If you want to know how to hook up a sketch with 'the rest of the page' for generate JavaScript work, have a look at http://processingjs.org/articles/PomaxGuide.html, but if that's not what you meant, please clarify your question =)