I find starting on a BF investigation to be very tedious. You start with some assertion string like "[-1] != [-1]" and try to reverse engineer what the real values involved were at the point of failure. I think the underlying problem is that our assert.js is really only capable of looking at bool conditions, so very valuable, and sometimes unreproducible , information is lost.
We could do better if we were using more of an assertion framework in JS tests, with matchers that can report about their inputs in more detail.
5 minutes of Googling revealed a few of them, like Should.js