Detect when scrolling has finished when using `scroll-behavior: smooth`

Question

What is the best way to detect when scrolling to an element on the page has finished? The spec says that "The scrolling box is scrolled in a smooth fashion using a user-agent-defined timing function over a user-agent-defined period of time. User agents should follow platform conventions, if any."

---

(2017-11-23) On a related note, Firefox 58 now has a chrome-only scrollend event.

Answer 1

The only feasible option appears to be to just wait until there aren't any more scroll events:

let timer; window.addEventListener( 'scroll', () => {     clearTimeout( timer );      timer = setTimeout( () => {         callback();     }, 300 ); }, { passive: true } );