Although it's not my stack of choice, it's generally a good starting point:

https://github.com/ixartz/SaaS-Boilerplate

JQuery.

I'm serious. Every time I see modern JS I look back at the JQuery ecosystem and it seems like we were all expelled from paradise. Elegant, modular, flexible, simple. Easy to use and extend. Even had a GUI library. No need for cross-compilation. No need for a package manager with a centralized namespace and a brittle and easily sabotaged dependency tree, because the web itself is the package manager (as God intended.)

Apache Guacamole

Extremely elegant ES5 project

https://github.com/apache/guacamole-client (mirror)

I remember jquery being an early classic with some annotated versions being available when I had an interest in learning js. No idea how much it has dated now.