> It's time for me to learn the fundamentals, so I can then learn libraries like React. There are more effective ways to learn. Instead of learning "bottom-up", start with your end-goal, e.g. creating apps with React. This is a good start: https://reactjs.org/tutorial/tutorial.html You'll find out what you need, and, more importantly, what you don't need to know along the way.
A pure, fundamentalist "bottom-up" approach will make you drown in boredom really fast, because you'll be learning very specific syntax details and language gotchas that you don't even know what they're useful for. But when you've been coding in React for a while, and you've had quite a few problems with the "this" expression, then going back to really understand how "this" works will be much more enlightening.
So my recommendation would also be this: Dive into React, or whatever is your end goal, and create stuff. Once you get stuck or feel like your knowledge of JS is inappropriate or you're falling for the same language gotchas without really understanding them, then read "You Don't Know JS".