In Node.js, is it normal to create several “server” objects, but only bind one to a port?

Question

I'm just about done reading "Node.js in Action", and I'm trying to put together the pieces of Node.js --> Connect --> Express. I have a question about the "servers" that we create in Node.

node_server = http.createServer();
connect_app = Connect();
express_app = Express();

In the code above, is it true that connect_app is basically a "subclass" of node_server ? (I know, this is JavaScript, so we don't really have subclassing, but I don't know what else to call it; extension?). And likewise express_app is basically a "subclass" of connect_app ? It's my understanding that all of these objects are servers which could be bound to a port and respond to requests, but that in practice we typically only bind ONE of them to a port and use it to proxy requests to other server objects.

Am I on the right track in learning this?

Answer 1

First of all, shake off the idea that there are 3 running servers - because there's only one.

Express is a framework that relies on Connect, which is another framework/set of middlewares. Further, Connect relies on the NodeJS's API (HTTP module). Basically an abstraction, one on top of another.

An analogy is that Express is a car, Connect is like an engine, NodeJS is the engine parts. You only have one running car (one server in your case), but multiple components powering it.

@josh3736 Has commented a better explanation how it works.