Socket.IO and Node.js Hello World Chat Application

We follow the Socket.IO advice at https://socket.io/get-started/chat/ to build a Hello World level Node.js web application ("node index" kickoff of server at command line with web browser URL of http://localhost:3000 client) and follow up with the suggested amendments to result in what you see here, and a tutorial about, later, at http://www.rjmprogramming.com.au/ITblog/socket.io-node.js-chat-application-primer-tutorial/ that includes code sources.