Indeed but it’s a bit like saying “you can not run tryton without gtk”.
jQuery + bootstrap is a bit like gtk (but we have to build everything from scratch), etc.
Of course it’s like having one gtk library per browser tab but that’s the way the web works …
Well if you go on their github page you’ll see that the project is 46% Javascript and 43.4% python, so yes they have a lot of javascript. And I think that their web client is distributed through their web addons:
And they use grunt, npm, etc to build their client.