I've been through this source code, really clean and well written modern javascript (as far as I can tell). I was completely new to this whole webstack, learned a ton about javascript and building front ends from this. I think an underrated way to get good at coding or even to learn whole new methods is to extend well written open source code. I find myself regularly working with high quality code off github, learning more from the developers on there than the developers I interact with at work.