[iOS] CSS Scroll Snap disables momentum-based scrolling

[Šime Vidas]

1. Open https://output.jsbin.com/kehuzan/quiet
2. Scroll the page

What happened: 

The scrolling animation does not have momentum.

Relevant CSS on test page:

html {
  scroll-snap-type: y proximity;
}

li {
  scroll-snap-align: start;
}

[Šime Vidas]

I’ve tested in Chrome and Firefox on Android. When I perform a fast scrolling operation, the scrolling continues until the velocity decreases to a certain threshold, at which point the browser snaps to an item.

But in Safari, as soon as I lift my finger from the swipe, it snaps. There is no fast scrolling velocity like in other browsers that prevents snapping for an additional second or two. This makes it impossible to scroll the page fast. You have to swipe over and over again to inch your way to the bottom of the page. I think this is way too limiting.

[Radar WebKit Bug Importer]

<rdar://problem/98224628>