Scroll columns area to right when children property is changed (#4517)

The feature to pin column could hide the rightmost column, which is
specified with children property of ColumnsArea.

The user is likely to see the column when the property changed, so scroll
the area in such cases.

1 files changed, 6 insertions, 5 deletions

diff --git a/app/javascript/mastodon/scroll.js b/app/javascript/mastodon/scroll.js
index c089d37db..44f95b17f 100644
--- a/app/javascript/mastodon/scroll.js
+++ b/app/javascript/mastodon/scroll.js
@@ -1,9 +1,9 @@
 const easingOutQuint = (x, t, b, c, d) => c * ((t = t / d - 1) * t * t * t * t + 1) + b;
 
-const scrollTop = (node) => {
+const scroll = (node, key, target) => {
   const startTime = Date.now();
-  const offset    = node.scrollTop;
-  const targetY   = -offset;
+  const offset    = node[key];
+  const gap       = target - offset;
   const duration  = 1000;
   let interrupt   = false;
 
@@ -15,7 +15,7 @@ const scrollTop = (node) => {
       return;
     }
 
-    node.scrollTop = easingOutQuint(0, elapsed, offset, targetY, duration);
+    node[key] = easingOutQuint(0, elapsed, offset, gap, duration);
     requestAnimationFrame(step);
   };
 
@@ -26,4 +26,5 @@ const scrollTop = (node) => {
   };
 };
 
-export default scrollTop;
+export const scrollRight = (node) => scroll(node, 'scrollLeft', node.scrollWidth);
+export const scrollTop = (node) => scroll(node, 'scrollTop', 0);