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

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 } );

Update: Firefox 109 and Chrome 110 now have a scrollend event: https://caniuse.com/mdn-api_element_scrollend_event