It's not, but I think the sourcemaps are there. The new UI is written in react. The real craziness is all the actual game content; look at the 'content' folder in devtools. There's a lot of JS that looks pretty similar to what I recall from the old pre-JS github repo. Lots of functions being declared straight on window. If you inspect the window object while playing the game you can get a glipse of the madness. I also spent some time digging around the webpack bundles after prettifying them in chrome but that is about what you'd expect.
I was trying the find .map files on my folder but couldn't, but then I realized you were playing from the fenoxo.com domain and it all made sense. I didn't even know you could get the source that way! (and you can download the files easily by doing .../release/<file>.js.map)
Taking a look now, I agree with you that it looks pretty similar to the Flash days and it would have been better for them to do a refactor.
Still, it doesn't look that bad when it comes to scaling (as in, adding new stuff in) and it is still better than a lot of JS code out there. I feel like a lot of bad decisions are on the "core" systems like the usage of the window object like you said, function names, conversion between scripts and in-game dialogue (while we can understand it just fine, I'm not sure if someone without knowledge of JS would be able to add something -- maybe they have some internal script that does that?), responsive design and file structure (like the lack of separation between text and game functions which causes file sizes to sky-rocket and the way they manage "rooms").
Maybe it's because I'm used to having to maintain or fix code that was forgotten in time with 0 documentation that causes TiTs code to not look bad.
edit: For those who want to see the mouse hover tooltips on mobile just replace all occurrences of
onMouseOver with
onTouchStart and
onMouseOut with
onTouchEnd on the
main.xxxxx.js file.