Exception debugging or: How to abuse JavaScript exception and debug tests

You must’ve used print-debugging at some point?

What about exception-debugging?

I doubt I’m the first to think of it, but I’m not sure if I’ve even seen it described or named anywhere.

How it works

If I want to see if my test case reaches some point in my code or not and I’m feeling particularly lazy – just throw an exception:

it('some test case', () => {
  const something = someFunction();

function someFunction() {
  // does my test reach this point?
  throw Error('yes it does');

Which will tell you if the test case reached that point in the code or not. A unique and easily recognizable exception message would be useful here.

Where would this even be useful?

If some tool is hiding the regular output text stream you could’ve used for print-debugging, you can use this technique instead. It’s a bit less useful, as it halts the execution or causes the code to jump up to the nearest exception handler. Considering this second point, this technique would also not be useful if you’re applying it within some context that is within an exception handler because we’d want to make sure the exception is fatal.


I realized now why no one has ever called it exception-debugging. This technique has a name: assertions.

However, using it in the context of figuring out whether your code reaches a certain point or not may be a less commonly used technique on its own, but quite useful when you don’t feel like firing up the debugger and setting up breakpoints and all else.