For me, when I want to deepen my understanding of a language or framework, my goto is usually a book on the topic. Right away, I’ll usually open up VIm and start playing around with code, which is fun and feels rewarding, but there’s something about reading that helps me to understand the inner workings and make sense of things faster. For that reason, I’m a long time advocate of The Rails Way, by Obie Fernandez.
Similarly with ES6, I’ve been soaking up bit and pieces from blog posts, documentation, and day to day development, but I wanted a good book to deep-dive.
The first section of the book points out may JS gotchas, but provides safe new alternatives that will steer you in the right direction.
The second section is concerned with new additions to the language, covering topics such as Iterators & Symbols, arrow functions and destructuring.
The fourth and final sections digs a little deeper into Metaprogramming.