Now that you already know the basics of javascript, it is time to proceed to node.js. Javascript previously existed only on our web browsers but then somebody thought of porting the javascript interpreter and gave it a home on the backend. Basically node.js provided the way for javascript to be able to have system functionalities like file handling, sockets, etc.
It is also notable that some javascript libraries that are known to work on the client-side (browsers) are also available on node.js. :)