It'd be fairly simple I think: a global object with .info(), .debug() etc methods. You'd have to make x-domain ajax calls to post back the message as the log server would have to run on another port. Various config options to change server, port, log-level defaults. And then a simple server to handle the posts and write out to log file on disk. You could even have a hosted/cloud service for those that didn't want to run their own logging server.