In theory, if we use TDD, we would not need to debug an application, but:

1. We have not always used TDD.
2. Not always work on our code.

In such cases, to debug an application node js enough two instructions:

In a terminal window.

npm install -g node-inspector

node-inspector &

And in another terminal window:

node --debug server.js

Then in the browser:

127.0.0.1/debug

And to follow step by step to find the error!