node.js mocha fallback to debugger on uncaught error

Question

Is there a way in node.js (ideally mocha too) to simulate the behavior of python

python -m pdb setup.py test

That will fallback to debug interface on if the program throws an uncaught exception.

EDIT

@robertklep suggested the undocumented breakOnException command which looks really awesome but not so much in practice:

test.js

var hello = {};
function testFunc () {
  anotherFunct();
}

function anotherFunct () {
  var b = hello.unfound;
}
testFunc();

And then it freezes at:

$ node debug test.js
< Debugger listening on port 5858
connecting to port 5858... ok
break in test.js:1
> 1 var hello = {};
  2 function testFunc () {
  3   anotherFunct();
debug> breakOnException
debug> c
debug> backtrace

EDIT2: test.js didn't yield an error in the first place. The above works fine.

Answer 1

Add this to your script:

process.on('uncaughtException', function() {
  debugger;
});

And start it with node debug script.js. That will drop you into the debugger on uncaught exceptions/errors.

To get this (somewhat) working for Mocha tests, you can add the lines above and follow the instructions here (specifically installing node-inspector and starting Mocha using --debug-brk).

EDIT: the Node debugger also has the ability to break on errors/exceptions:

$ node debug script.js
debug> breakOnException
debug> c
...