Being a frontend developer means not only knowing your tools pretty well but also understanding how and why they behave the way they do. JavaScript is a language that is very easy to get started but is actually more complex than it looks. That's the approach of Mark Daggett on the book Expert JavaScript.
A Conversation About JavaScript
What I really liked about this book is that it brings a very personal touch to a very technical book. Mark promptly states that it is a compilation of his favourite topics, like a collage of side notes. Similar style used by Crockford's "The Good Parts".
The topics range from objects to prototype, nodebots to unit testing. Each is very well written with just the right amount of complexity to cater for the more experienced coders.
Conclusion
Expert JavaScript is a perfect choice of book for those moments when you need to see the language you use everyday from a different angle. Sometimes you'll revisit concepts you already know and sometimes you'll have to re-read the same chapter over and over to digest all the information available.
The book is available at http://www.apress.com/9781430260974.