Fix scrolling behavior (#7151)

* Update React.JS

* Use React's new lifecycles for scrollable lists

* Clean up dead code

* Make CodeClimate happy

1 files changed, 12 insertions, 20 deletions

diff --git a/app/javascript/mastodon/components/scrollable_list.js b/app/javascript/mastodon/components/scrollable_list.js
index ee07106f7..fd6858d05 100644
--- a/app/javascript/mastodon/components/scrollable_list.js
+++ b/app/javascript/mastodon/components/scrollable_list.js
@@ -34,7 +34,7 @@ export default class ScrollableList extends PureComponent {
   };
 
   state = {
-    lastMouseMove: null,
+    fullscreen: null,
   };
 
   intersectionObserverWrapper = new IntersectionObserverWrapper();
@@ -43,7 +43,6 @@ export default class ScrollableList extends PureComponent {
     if (this.node) {
       const { scrollTop, scrollHeight, clientHeight } = this.node;
       const offset = scrollHeight - scrollTop - clientHeight;
-      this._oldScrollPosition = scrollHeight - scrollTop;
 
       if (400 > offset && this.props.onLoadMore && !this.props.isLoading) {
         this.props.onLoadMore();
@@ -59,14 +58,6 @@ export default class ScrollableList extends PureComponent {
     trailing: true,
   });
 
-  handleMouseMove = throttle(() => {
-    this._lastMouseMove = new Date();
-  }, 300);
-
-  handleMouseLeave = () => {
-    this._lastMouseMove = null;
-  }
-
   componentDidMount () {
     this.attachScrollListener();
     this.attachIntersectionObserver();
@@ -76,21 +67,26 @@ export default class ScrollableList extends PureComponent {
     this.handleScroll();
   }
 
-  componentDidUpdate (prevProps) {
+  getSnapshotBeforeUpdate (prevProps) {
     const someItemInserted = React.Children.count(prevProps.children) > 0 &&
       React.Children.count(prevProps.children) < React.Children.count(this.props.children) &&
       this.getFirstChildKey(prevProps) !== this.getFirstChildKey(this.props);
+    if (someItemInserted && this.node.scrollTop > 0) {
+      return this.node.scrollHeight - this.node.scrollTop;
+    } else {
+      return null;
+    }
+  }
 
+  componentDidUpdate (prevProps, prevState, snapshot) {
     // Reset the scroll position when a new child comes in in order not to
     // jerk the scrollbar around if you're already scrolled down the page.
-    if (someItemInserted && this._oldScrollPosition && this.node.scrollTop > 0) {
-      const newScrollTop = this.node.scrollHeight - this._oldScrollPosition;
+    if (snapshot !== null) {
+      const newScrollTop = this.node.scrollHeight - snapshot;
 
       if (this.node.scrollTop !== newScrollTop) {
         this.node.scrollTop = newScrollTop;
       }
-    } else {
-      this._oldScrollPosition = this.node.scrollHeight - this.node.scrollTop;
     }
   }
 
@@ -143,10 +139,6 @@ export default class ScrollableList extends PureComponent {
     this.props.onLoadMore();
   }
 
-  _recentlyMoved () {
-    return this._lastMouseMove !== null && ((new Date()) - this._lastMouseMove < 600);
-  }
-
   render () {
     const { children, scrollKey, trackScroll, shouldUpdateScroll, isLoading, hasMore, prepend, emptyMessage, onLoadMore } = this.props;
     const { fullscreen } = this.state;
@@ -157,7 +149,7 @@ export default class ScrollableList extends PureComponent {
 
     if (isLoading || childrenCount > 0 || !emptyMessage) {
       scrollableArea = (
-        <div className={classNames('scrollable', { fullscreen })} ref={this.setRef} onMouseMove={this.handleMouseMove} onMouseLeave={this.handleMouseLeave}>
+        <div className={classNames('scrollable', { fullscreen })} ref={this.setRef}>
           <div role='feed' className='item-list'>
             {prepend}