Ask HN: JavaScript UI framework

I am a long time C/C++/Python developer and have a lot of experience in programming with Qt. I am trying to learn something new and got an opportunity at work to write a small Web GUI to visualise some sensor data. For that purpose I went with react and the data aquisition works well with AJAX and my custom c++ cgi app but I am missing the whole "nice UI" and theme part. If this app works well, I will write another, which will need a tree view and drag and drop functionality. My main question is:

What whould you guys recommend?

I feel that there are too much frameworks in web world and am not sure which ones are good. I've researched a bit, tried Polymer but it doesn't feel mature enough. ExtJS is priced out of our league. Material UI is missing a tree widget and I have no idea how hard is it to implement drag and drop there.

So my current picks are dojo or wt. However may say dojo misses documentation, the architecture is old and it's hard to debug. Also any optionion on wt and other toolits would be highly appreciated.