Merge pull request #144 from inokawa/refactor-reset-cache

Refactor resetCache

src/core/cache.ts

@@ -133,33 +133,42 @@ export const estimateDefaultItemSize = (cache: Writeable<Cache>) => {
       median(measuredSizes);
 };
 
-export const resetCache = (
-  length: number,
-  itemSize: number,
-  cache?: Cache
-): Cache => {
+export const initCache = (length: number, itemSize: number): Cache => {
   const sizes: number[] = [];
   const offsets: number[] = [];
   for (let i = 0; i < length; i++) {
-    const size = cache && cache._sizes[i];
+    sizes.push(UNCACHED);
+    // first offset must be 0
+    offsets.push(i === 0 ? 0 : UNCACHED);
+  }
+
+  return {
+    _defaultItemSize: itemSize,
+    _length: length,
+    _measuredOffsetIndex: 0,
+    _sizes: sizes,
+    _offsets: offsets,
+  };
+};
+
+export const updateCache = (cache: Writeable<Cache>, length: number) => {
+  const sizes: number[] = [];
+  const offsets: number[] = [];
+  for (let i = 0; i < length; i++) {
+    const size = cache._sizes[i];
     sizes.push(exists(size) ? size : UNCACHED);
 
     if (i === 0) {
       // first offset must be 0
       offsets.push(0);
     } else {
-      const offset = cache && cache._offsets[i];
+      const offset = cache._offsets[i];
       offsets.push(exists(offset) ? offset : UNCACHED);
     }
   }
 
-  return {
-    _defaultItemSize: cache ? cache._defaultItemSize : itemSize,
-    _length: length,
-    _measuredOffsetIndex: cache
-      ? min(cache._measuredOffsetIndex, length - 1)
-      : 0,
-    _sizes: sizes,
-    _offsets: offsets,
-  };
+  cache._length = length;
+  cache._measuredOffsetIndex = min(cache._measuredOffsetIndex, length - 1);
+  cache._sizes = sizes;
+  cache._offsets = offsets;
 };

src/core/store.ts

@@ -1,6 +1,6 @@
 import {
   findStartIndexWithOffset,
-  resetCache,
+  initCache,
   getItemSize,
   computeTotalSize,
   findEndIndex,
@@ -10,6 +10,7 @@ import {
   setItemSize,
   hasUnmeasuredItemsInRange,
   estimateDefaultItemSize,
+  updateCache,
 } from "./cache";
 import type { CacheSnapshot, Writeable } from "./types";
 import { abs, exists, max, min } from "./utils";
@@ -92,13 +93,13 @@ export const createVirtualStore = (
 ): VirtualStore => {
   const shouldAutoEstimateItemSize = !itemSize;
   const initialItemSize = itemSize || 40;
+  const cache =
+    (cacheSnapshot as unknown as Cache | undefined) ??
+    initCache(elementsCount, initialItemSize);
   let viewportSize = initialItemSize * max(initialItemCount - 1, 0);
   let scrollOffset = 0;
   let jumpCount = 0;
   let jump: ScrollJump = 0;
-  let cache =
-    (cacheSnapshot as unknown as Cache | undefined) ??
-    resetCache(elementsCount, initialItemSize);
   let _scrollDirection: ScrollDirection = SCROLL_IDLE;
   let _isManualScrolling = false;
   let _resized = false;
@@ -341,7 +342,7 @@ export const createVirtualStore = (
     _updateCacheLength(length) {
       // It's ok to be updated in render because states should be calculated consistently regardless cache length
       if (cache._length === length) return;
-      cache = resetCache(length, initialItemSize, cache);
+      updateCache(cache as Writeable<Cache>, length);
     },
   };
 };