Reading through how React does what it does by reading the source code can change how you look at designing your own web components.
Beating your head on the core of the Phaser library can give you a handle on how to handle keyboard interactions well, or intersections between DOM elements.
It is not easy to read them, they often have utility functions that are built into the library, so you’ll end up scrolling back and forth, or drawing yourself a map and guide. It happens. But there is a LOT of meat in reading open-source libraries and frameworks. Even if you continue to use the framework, you’ll find you use it more intelligently and efficiently.