Is there a way of enabling failure logs in prince? I'm getting 'success' even though I'm pretty sure my JavaScript is crashing - it was using Array.forEach() which is on the product roadmap (and so I guess doesn't work) but its very hard to diagnose errors other than my JS not working and I don't know why?

JavaScript exceptions and other errors should show up in the error log, which can be saved to a file with the --log option.

Is there a definitive list of which things aren't supported by your JS engine? You mention a few DOM properties, but I only found out about the Array.forEach() thing by accident as I was looking through your product roadmap.

It would be difficult to maintain such a list as browsers keep adding more properties.

We are planning to do more of this spec checking later in the year, though.