Error-handling middleware is different from the rest of the middleware because it takes four arguments (error, request, response, next) instead of three.

Another thing we should take into consideration is that the custom error-handling middleware should be placed after the rest of the middleware. If we don't do the placement, when we call next(err), Express will not find any custom error handler (because the middleware is loaded in order) and will default to the built-in error handler.

Now that we know this, let's create a custom error handler that we can use during development to show us the relevant stack trace information. It should exclude core native method calls and also the NPM dependencies (node_modules). The handler should display the source code for each method call that caused the error.

We will use the stack-trace module to parse the stack trace (get line number, file name, and so on) and the async-each module to handle reading the files and...