This is a series of books diving deep into the core mechanisms of the JavaScript language. The first edition of the series is now complete. Also, these first-edition books are now out of print and can no longer be purchased. They can only be read for free online here in this markdown format.
Repo Link
The content of these books was released here, and the books were also edited, produced, and published through O'Reilly (2014-2015).
He also have some JS training material available in on-demand video format. He teach courses through Frontend Masters. You can find all his courses here.
These first-edition books are complete and published and will not be changed in any way, so there's no further need for contributions. They will remain here for posterity, but are not being maintained. See the 2nd edition books for the active work in this repository.