Personally, I didn't find much to learn about JavaScript because most things in JavaScript are almost like things in Perl except that JavaScript is more verbose in important places like anonymous functions. The one thing that I found very instructive is the discussion of how to implement classical inheritance in JavaScript - that taught me the missing bits about how the object model is classless and how one can abuse it to implement real classes.

I guess that the Rhino book is the definitive reference to JS, but I haven't looked into it.

One day, I might actually write the Perl Traveler's Language Guidebook that teaches languages as "Differences from Perl"...