Debugging in Old Browsers

A short while back, I redid my Random Quote Machine project using the excellent Simpsons Quotes API by fellow camper JLuboff. I’m very happy with the result in modern browsers, but in IE8 it not only looks appallingly bad, it also completely fails to function.

Now, IE8 is a very old browser and its market share is small even among IE users. What I’m curious about is more the general issue of discovering and debugging these compatibility issues as an individual developer or a small team without legions of testers. Are there tools you can use to check which parts of your code will be problematic in certain browsers? I’m mainly talking about scripts here - with CSS it’s usually pretty clear what’s not working (gradients, shadows, semi-transparency, SVGs…), but there’s no such visual indication when your script fails to run entirely.

Using IE8’s “developer tools”, such that they are, is out of the question - they don’t throw up a single error. The status bar even shows “Done”, rather than the infamous “Done with errors on page”. So how would one even start debugging this?

For reference:
Github Source
Github Pages