Learning the fundamentals
The thing is… we’ve got too many developers who only know how to build with libraries, and not enough who understand the fundamentals.
If you know how the web platform works, the code you write with libraries is better. You can learn new libraries more easily. You become better at picking the right tool for the job. You realize that a lot of times, you don’t need a library (and understand when reaching for one adds more value than it costs).
You can absolutely learn a library first and back into the fundamentals. A lot of folks do. Hell, that’s how I learned.
But the fundamentals will always be valuable, and they’ll always outlive the flavor-of-the-month tools the industry is currently using.