Hi Michal,
TL;DR : The javascript you’re talking about is part of a service.
It’s been a while since I’ve attended ADSD, but from what I remember, Udi definitely doesn’t intent to say that everything in the UI belongs to branding. Branding does what its name implies, do everything related to branding. Because the look and feel, styling, etc. is overarching multiple services and that’s why there’s a branding service that does nothing else.
However the javascript that is related to business logic, most certainly belongs to a specific service. A service is the technical authority for everything from database (data storage) to the user interface. So that includes HTML and JavaScript.
Then there’s also IT/OPS, which is not responsible for business logic but rather infrastructural related code, to put it in my own simple words. So libraries for logging, authentication, but also other stuff go in there and are decided by the team that runs IT/OPS, usually the architects and people that decide what features will be build and what goes in which service. They also make sure composition of the screen and the viewmodel is possible.