“Svelte and Sapper in Action” by Mark Volkmann is a good book.
There are also 10$ courses on Udemy:

1. https://www.udemy.com/course/sveltejs-the-complete-guide/
2. https://www.udemy.com/course/svelte-tutorial-and-projects-course/ (sapper is not included here)
3. Good introduction to Sapper course by Net Ninja https://www.youtube.com/watch?v=-1hj5O-tQXo&list=PL4cUxeGkcC9gdr4Qhx83gBBcID-KMe-PQ&index=1

Yes, Sapper is Node js “app lvl” framework from Svelte’s creator. There is also an Elder.js (a static site generator, but can be also used as Sapper) https://elderguide.com/tech/elderjs/ Btw how easy is to jump into Phoenix(and Elixir) as a JS dev?

Yeah, JS is specific … although it has become much nicer to use in recent years how much Erlang does one need to know to be productive for Phoenix?