What are the javascript open source implementations of the PubSubHubbub protocol publishing side first
First, you may want to fix your title as it's PubSubHubbub... not PubHubSubbub! Then, it depends on what side you're asking? Publisher, Subscriber, Hub?
Since all of them need to be able to server files or reply to incoming HTTP requests, you will need to build one with Node.JS, because I don't know of any yet. However, keep in mind that the publisher and subscriber are really easy to implement, so creating a library may actually not make a lot of sense, because you would quickly bump into the limitation of said library.