fix: disable smooth scroll for users who prefer reduced motion (#958)

src/routes/_utils/smoothScroll.js

@@ -1,3 +1,5 @@
+import { store } from '../_store/store'
+
 // via https://github.com/tootsuite/mastodon/blob/f59ed3a4fafab776b4eeb92f805dfe1fecc17ee3/app/javascript/mastodon/scroll.js
 const easingOutQuint = (x, t, b, c, d) =>
   c * ((t = t / d - 1) * t * t * t * t + 1) + b
@@ -62,7 +64,10 @@ function testSupportsSmoothScroll () {
 export const hasNativeSmoothScroll = process.browser && testSupportsSmoothScroll()
 
 export function smoothScroll (node, topOrLeft, horizontal) {
-  if (hasNativeSmoothScroll) {
+  if (store.get().reduceMotion) {
+    // don't do smooth-scroll at all for users who prefer reduced motion
+    node[horizontal ? 'scrollLeft' : 'scrollTop'] = topOrLeft
+  } else if (hasNativeSmoothScroll) {
     return node.scrollTo({
       [horizontal ? 'left' : 'top']: topOrLeft,
       behavior: 'smooth'