Mostly pre-es6, but this is my favorite "intermediate -> advanced" JavaScript book: https://www.amazon.com/Effective-JavaScript-Specific-Software-Development/dp

Mostly pre-es6, but this is my favorite "intermediate -> advanced" JavaScript book: https://www.amazon.com/Effective-JavaScript-Specific-Software-Development/dp/0321812182 https://www.amazon.com/Effective-JavaScript-Specific-Softwar... There are gaps/things that have changed since the book came out, but this is a really great resource for understanding the core JS language.