With this book you will:
Understand why JavaSript’s unique array, string, and number characteristics may delight or confound you
Learn how natives provide object wrappers around primitive values
Dive into the coercion controversy—and learn why this feature is useful in many cases
Comments about oreilly You Don't Know JS: Types & Grammar:
I don't think I've ever read a book this good on a programming topic. Everything was explained well, to the point, and extremely interesting. This, in my opinion, tops the first two parts of the series even though it's an early release, as I didn't feel like having to read some paragraphs twice (which I expect to often happen with in-depth discussions of unknown/unexpected technical issues). I was left with easily understanding many 'wtf' examples on JS that float around the internet outside of the examples given in the book, and getting a lot of ideas on how to make my code look nicer, and work better.
Bottom Line Yes, I would recommend this to a friend