As a solo freelancer, I have developed and maintained an internal management web app for a small wine importing company from 2012 to this day: a huge portion of its 15+ KLOCs codebase is ExtJS 4 (the rest is the Python backend) and I have mixed feelings about it.. Given the heavy use of complex widgets and layouts (the Grid component in particular does about everything you could ever imagine, and probably more), I often think that porting to another (more modern?) framework would be almost impossible.. I regularly browse what's available, and I'm certain that an upgrade based on a React + Material stack of some kind would be an interesting evolution, but I'm not sure I have the courage to undertake such an endeavor (not to mention the fact that my client probably wouldn't see the immediate advantage). Despite the often-mentioned appreciable learning curve (which I can't really appreciate anymore since it's been amortized on so many years and hacking sessions), here are four things I appreciate the most of Ext JS:
1. The fact that well-written Ext JS code has a very "declarative" feel to it, despite being JS
2. The documentation is very complete and written with love
3. The dev environment I've been using is very monolithic, and seems very far from the incredibly scattered stack of tools that seem to slowly poison the JS landscape and culture, and which we often read articles about on HN
4. The community (at least when I was interacting with it on a more regular basis) is great