Node.js and the Javascript Age

The JavaScript age is about event streams. Modern web pages are not pages, they are event-driven applications through which information moves. The core content vessel of the web — the document object model — still exists, but not as HTML markup. The DOM is an in-memory, efficiently-encoded data structure generated by JavaScript.

… The principal role of the server is to ship an application to the client (JavaScript), along with data (JSON), and let the client weave those into a DOM.