David Marr

Debugging with NodeJS and Expresso

NodeJS

git clone https://github.com/joyent/node.git

Expresso

git clone https://github.com/visionmedia/expresso.git

After installing NodeJS and Expresso you will have to make a change to your Expresso file to allow for debugging.

Add the following statement to your code to set a breakpoint in the debugger:

debugger;

Next, run the following to start up the NodeJS debugger and use Expresso for your unit tests.

Using TextMate

mate $(which expresso)

Using vim

vim $(which expresso)

Change the first line to read:

#!/usr/bin/env node debug

Executing your tests with expresso now uses the node debugger.^*

expresso test.js

For those looking for a browser based debugging environment, check out node-inspector.

Node Inspector

git clone https://github.com/dannycoates/node-inspector.git

To get this to work with Expresso, I had to change the hashbang to be:

#!/usr/bin/env node —debug-brk

node-inspector &

Now, running expresso test.js will open your file in a web browser for debugging. You will have to point your browser to node-inspector and you can explore your breakpoints and watch variables just like you were in WebKit.

Happy coding, twitternets!

* There are mixed feelings about this in the develosphere, as debugging unit tests is a bit like betting on black /and/ red. I am illustrating how to do it, not advocating its use. Personally I think its better to rely on the unit testing framework to surface errors but stepping through with debugger; statements is sometimes the only way to dive deep into the problem.