Let's round out the walkthrough of app.js by discussing what middleware functions do for our application. We have an example at the end of the script:
app.use(function(req, res, next) {
var err = new Error('Not found');
err.status = 404;
next(err);
});
The comment says catch 404 and forward to error handler. As you probably know, an HTTP 404 status means the requested resource was not found. We need to tell the user their request wasn't satisfied, and maybe show them a picture of a flock of birds pulling a whale out of the ocean. This is the first step in doing so. Before getting to the last step of reporting this error, you must learn how middleware works.
We do have a middleware function right in front of us. Refer ...
