[foxfluff]

> It would be very interesting to develop a modern web based purely on declarative content (modern HTML/CSS).

For sure. I think some scripting could also potentially be implementable without massive fingerprinting / privacy implications. E.g. pure compute scripts, form validation, etc. that has no practical way to smuggle any data out of your browser. Anything that sends a request would have to be statically derived (or explicit user input as into form).

[southerntofu]

Functional data pipelines without side-effects could do the trick indeed. It would also make it a lot easier to debug for performance issues, and the browser could be more clever about optimizations: for example if you've got a loop changing DOM elements, maybe you could wait for the loop to finish before starting a re-render... something that's impossible to do with JS-based rendering where global page state may change under your feet at any given time.

EDIT: Just for the sake of mentioning, simple/obvious computations for interactivity was the promise of GNU's libreJS project. I'm unaware of the current state of it, though.