Merge pull request #313 from inokawa/prepend-jump

Improve jump compensation after prepending
inokawa · Jan 4, 2024 · 9bff11e · 9bff11e
2 parents c0ea976 + 6f014c6
commit 9bff11e
Showing 1 changed file with 16 additions and 9 deletions.
diff --git a/src/core/store.ts b/src/core/store.ts
@@ -29,6 +29,14 @@ export type ScrollDirection =
  | typeof SCROLL_DOWN
  | typeof SCROLL_UP;
 
+const SCROLL_BY_NATIVE = 0;
+const SCROLL_BY_MANUAL_SCROLL = 1;
+const SCROLL_BY_PREPENDING = 2;
+type ScrollMode =
+ | typeof SCROLL_BY_NATIVE
+ | typeof SCROLL_BY_MANUAL_SCROLL
+ | typeof SCROLL_BY_PREPENDING;
+
 /** @internal */
 export const ACTION_ITEM_RESIZE = 1;
 /** @internal */
@@ -164,8 +172,7 @@ export const createVirtualStore = (
  let pendingJump = 0;
  let _flushedJump = 0;
  let _scrollDirection: ScrollDirection = SCROLL_IDLE;
- let _prepended = false;
- let _isManualScrolling = false;
+ let _scrollMode: ScrollMode = SCROLL_BY_NATIVE;
  let _frozenRange: ItemsRange | null = isSSR
  ? [0, max(ssrCount - 1, 0)]
  : null;
@@ -281,8 +288,6 @@ export const createVirtualStore = (
  const updated = payload.filter(
  ([index, size]) => cache._sizes[index] !== size
  );
- const isJustPrepended = _prepended;
- _prepended = false;
 
  // Skip if all items are cached and not updated
  if (!updated.length) {
@@ -299,7 +304,7 @@ export const createVirtualStore = (
  // Keep end to stick to the end
  diff = calculateJump(cache, updated, true);
  } else {
- if (isJustPrepended) {
+ if (_scrollMode === SCROLL_BY_PREPENDING) {
  // Keep distance from end immediately after prepending
  // We can assume jumps occurred on the upper outside
  diff = calculateJump(cache, updated);
@@ -360,7 +365,9 @@ export const createVirtualStore = (
  const [shift, isAdd] = updateCacheLength(cache, payload[0], true);
  applyJump(isAdd ? shift : -min(shift, distanceToEnd));
 
- _prepended = isAdd;
+ if (isAdd) {
+ _scrollMode = SCROLL_BY_PREPENDING;
+ }
  mutated = UPDATE_SCROLL_STATE;
  } else {
  updateCacheLength(cache, payload[0]);
@@ -389,7 +396,7 @@ export const createVirtualStore = (
  if (
  !isJustJumped &&
  // Ignore until manual scrolling
- !_isManualScrolling
+ _scrollMode === SCROLL_BY_NATIVE
  ) {
  _scrollDirection = delta < 0 ? SCROLL_UP : SCROLL_DOWN;
  }
@@ -425,12 +432,12 @@ export const createVirtualStore = (
  mutated += UPDATE_SCROLL_STATE;
  }
  _scrollDirection = SCROLL_IDLE;
- _isManualScrolling = false;
+ _scrollMode = SCROLL_BY_NATIVE;
  _frozenRange = null;
  break;
  }
  case ACTION_MANUAL_SCROLL: {
- _isManualScrolling = true;
+ _scrollMode = SCROLL_BY_MANUAL_SCROLL;
  break;
  }
  case ACTION_BEFORE_MANUAL_SMOOTH_SCROLL: {