Fixed scrolling for Firefox by adding scroll context in state

Author: Eric Vallee

src/constants.js

@@ -3,6 +3,8 @@ export const ALIGN_CENTER = 'center';
 export const ALIGN_END = 'end';
 export const DIRECTION_VERTICAL = 'vertical';
 export const DIRECTION_HORIZONTAL = 'horizontal';
+export const SCROLL_CHANGE_OBSERVED = 'observed';
+export const SCROLL_CHANGE_REQUESTED = 'requested';
 
 export const scrollProp = {
   [DIRECTION_VERTICAL]: 'scrollTop',

src/index.js

@@ -7,6 +7,8 @@ import {
   ALIGN_START,
   DIRECTION_VERTICAL,
   DIRECTION_HORIZONTAL,
+  SCROLL_CHANGE_OBSERVED,
+  SCROLL_CHANGE_REQUESTED,
   positionProp,
   scrollProp,
   sizeProp,
@@ -48,6 +50,7 @@ export default class VirtualList extends PureComponent {
       this.props.scrollToIndex != null && this.getOffsetForIndex(this.props.scrollToIndex) ||
       0
     ),
+    scrollChangeReason: SCROLL_CHANGE_REQUESTED
   };
 
   _styleCache = {};
@@ -102,21 +105,23 @@ export default class VirtualList extends PureComponent {
     if (nextProps.scrollOffset !== scrollOffset) {
       this.setState({
         offset: nextProps.scrollOffset,
+        scrollChangeReason: SCROLL_CHANGE_REQUESTED,
       });
     } else if (
       scrollPropsHaveChanged ||
       nextProps.scrollToIndex && itemPropsHaveChanged
     ) {
       this.setState({
         offset: this.getOffsetForIndex(nextProps.scrollToIndex, nextProps.scrollToAlignment, nextProps.itemCount),
+        scrollChangeReason: SCROLL_CHANGE_REQUESTED,
       });
     }
   }
 
   componentDidUpdate(nextProps, nextState) {
     const {offset} = this.state;
 
-    if (nextState.offset !== offset) {
+    if (nextState.offset !== offset && nextState.scrollChangeReason === SCROLL_CHANGE_REQUESTED) {
       this.scrollTo(offset);
     }
   }
@@ -129,7 +134,7 @@ export default class VirtualList extends PureComponent {
       return;
     }
 
-    this.setState({offset});
+    this.setState({offset, scrollChangeReason: SCROLL_CHANGE_OBSERVED});
 
     if (typeof onScroll === 'function') {
       onScroll(offset, e);