This deserves a much better answer, but I'll just say this for now. Svelte is declarative/imperative (but mostly imperative) and also not based on functional principles. React is definitely more on the declarative side. And Hyperapp is essentially Elm in JavaScript, so it's as declarative/functional/immutable as the definition allows for.
Maybe the person that said Svelte was more declarative was only familiar with an older incarnation of Hyperapp that wasn't completely based on functional principles, or maybe they're using a more loose but inaccurate definition of declarative (kind of like how people often say "theory" when they actually mean "hypothesis").
What do you think the advantages and disadvantages are? I remember briefly looking into Hyperapp and mostly liking it, but still wasn't sure which JS framework is the best choice (the other one I liked was Vue).
Some time after that I learned about Svelte and very quickly concluded that this would be my choice, everything just feels right about it. For the record, I've only done a small project in Svelte.
That's fine. If you're already happy with Svelte, I encourage you to explore more with it. Try building a couple of non-trivial projects and keep learning about your craft. If you're also into computer science, I recommend you look into functional programming if you haven't done so yet. Then look at Svelte again. Try React too. Check out Elm.
I can tell you that Hyperapp is not for everyone. If you want to write pure, immutable, functional JavaScript and think hard about client side app architecture (unidirectional state management, controlled side effects, toggleable subscriptions), then you'll love it.
If you are looking for a more accommodating, meet-in-the-middle kind of approach where you can mix programming styles, and don't want to think much about those things I mentioned above, then React, Vue, Svelte are all great choices.
V2 will be released in a few months, so do circle back to Hyperapp then to see how you like it again.
Finish the site and docs, merge the minimizations branch (has memory performance improvements, and brings it down to 1690 bytes gzipped / 1528 bytes brotlified total), add tests, then we can officially proclaim V2.
Definitely not planning to remove the current state or anything haha.
Svelte is more declarative. Svelte is also a compiler, which generates very efficient code for keeping the dependent parts of the DOM up-to-date when the app state changes, effectively moving the vDOM diffing cost from runtime to compile-time.
