[xendipity]

Agreed, the You Don't Know JS series is very good for solid fundamentals.

At some point, that knowledge can then be applied by learning more advanced language features such as implementing Proxies, Generators, and template literal functions.

To do so, some here are suggesting you read the language spec. I think Rau schmaer's series "Exploring ES6" [0] (and then ES7/8/9) is a great alternative to the actual spec. In those books he basically goes through the new features of each version of the language and does the deepest dive I've seen, with examples and references to the spec.

[0] - https://exploringjs.com/es6.html