$(window).scroll in vanilla JavaScript
Question 1
window.onscroll = function() { console.log('scrolling');};or if your targeted browsers support addEventListener :
window.addEventListener('scroll', function() { console.log('scrolling');});Question 2
In my opinion, if you're just scrolling from one section to a another section of your page, and not having some sort of constantly running scrolling movement, you're fine doing this without using requestAnimationFrame.
You can find good implementations of scrolling to a particular part of the window in pure javascript, I suggest checking out their source(or even using them).