You’ll find everything from testing tools and frameworks to higher-level game engines.
The whole website was also released for free on GitHub. You can pull a copy of the repo to keep locally or even submit changes of your own accord. It’s maintained by William Oliveira with infrequent updates as needed.
Be warned that the guide is long and detailed, so don’t expect to get through it all in a weekend.
Instead take your time and read through everything. Try to digest confusing areas and ask for help online as you need it. This guide can offer everything you need to become an advanced JS dev if you only take the time to study.