Also "You Don't Know JS Yet" has some depth in it https://github.com/getify/You-Dont-Know-JS
Also more to your question, "The Browser Hacker's Handbook" and "The Web Application Hacker's Handbook" I also think are really helpful in understanding how browsers work. Sadly a not better documented subject.
Visiting the list of APIs on Mozilla's website is also helpful.
nowadays I usually refer to MDN docs and one of the guides like above when guidance is needed.
It discusses great edge cases of JS while explaining why or how come they are like this where possible.
For a format that is easier to consume and isn't marketing content, see:
[1]https://github.com/getify/You-Dont-Know-JS [2]https://eloquentjavascript.net/
"You don't know JS": https://github.com/getify/You-Dont-Know-JS
"How browsers work": https://www.html5rocks.com/en/tutorials/internals/howbrowser...
"High performance browser networking": https://hpbn.co/
I think you may find that some of those "bad design decisions" are actually not so bad, or at least manageable, once you will have read through the book.
on edit: one reason the specs are not enough is generally specs will tell you what needs to be implemented but a good book, like these ones, will tell you how it has been implemented or what the spec implies for implementation and what all that will mean for you as a user of the language.
After watching that I would recommend https://github.com/getify/You-Dont-Know-JS and that should give one a solid base.
[0] - https://github.com/getify/You-Dont-Know-JS
[1] - https://www.ecma-international.org/publications/standards/Ec...
I have bookmarked few other links from HN
https://news.ycombinator.com/item?id=13979472
https://github.com/getify/You-Dont-Know-JS
https://www.robinwieruch.de/javascript-fundamentals-react-re...
That said, if you want a comprehensive read about Javascript, there's You don't know JS: https://github.com/getify/You-Dont-Know-JS
The main thing is to just pick one that is popular and has been around for a couple years (not something just released) and start coding.
Work on your JS fundamentals - https://github.com/getify/You-Dont-Know-JS
On the backend, use google cloud or azure. There is a ton of code already written for any kind of app/website usecase you can ever imagine. Just reuse it.
Today's Mark Zuckerberg would just be plugging in piece that already exist. Focusing less on code and more on the User needs.