I'm excited about this book. And, I really wish there was a book that showed how a developer using a more modern language like JavaScript could use it to customize Emacs.
This is why VSCode is winning, because it embraces modern languages in a really powerful way. When I install a new Emacs into a new debian machine, i still struggle to get package installation working. But I'm getting really worried about the direction Microsoft is taking with VSCode and wish I could be as productive in Emacs. Opening up that environment to modern developers who could tweak their own tools would be amazing and revolutionary.