Learning node.js/express.js: What's the deal with bin/www?

Question

I've seen tutorials for express.js such as this which starts from scratch with their own app.js file and forgoes using the express generator.

My question: for beginner who's trying to grasp just how to use these tools and make a basic web application should I be concerned with bin/www or should I just be defining the port within app.js?

The only functionality I currently understand in bin/www is setting the port. Is the express generator simply bloated with edge case functionality which is too much for a beginner?

Answer 1

Here is the reason, stated succinctly by an express maintainer:

So you can require('./app') from external files and get the express app that is not listening on any port (think unit tests and the like).

source

Answer 2

app.js

• contains all the middleware(body-parser,morgan,etc) and routes.
• it exports app object at the last.

www

• here it creates a httpServer and passes app as the handler

var server = http.createServer(app);

• besides also sets the port server.listen(port);
• also sets the functions to be called if there is an error while starting the server: server.on('error', onError);

Explanation so, basically it removes all the create and start server code from your app.js and let you focus only on the application logic part. Note: If you see in package.json file you would note this:

"scripts": {   "start": "node ./bin/www" } 

this means if you type in terminal npm start then it will automatically start the ./bin/www file.