So here I am claiming to be a so-called "experienced" JavaScript developer, thinking that I pretty much know everything about this language, but in fact I don't. It's like driving a car for many years, and you start thinking that you're the best. The true fact of the matter is that your driving skills are becoming quite rusty and if you are not careful it will become very dangerous.
It never hurts to have a serious look at yourself in the mirror once in awhile, do it sometime and you'll feel much better about yourself.
Since I am never too old to learn new stuff, I like to discover the future while it is still happening. More and more I've been getting interesting in how the JavaScript language is evolving, namely the new and upcoming ES6 features. This is really cool stuff and shouldn't be missed.
So I went over to the Leanpub website and found myself a couple good sources, namely Exploring ES6 and Setting up ES6 by Axel Rauschmayer.
These books are fairly technical and difficult to understand, but beautifully written nonetheless. I figured that in order to maximize my learning experience I'd have to take one step back and refresh my knowledge of the JavaScript basics. Not just some easy introductory book but an intense and truly in-depth exploration of the technical details.
Since this Axel person is obviously very smart I figured what the heck three books by him must be the magical combination to success. So I bought his other book.
A tough but fulfilling read, highly recommended. Speaking JavaScript is also available for free online, but I'm still pretty old-fashioned and had to have another book for my immense computer library.