Refactor

src/core/resizer.ts

@@ -5,7 +5,7 @@ import {
   type VirtualStore,
 } from "./store";
 import { type ItemResize } from "./types";
-import { exists, max } from "./utils";
+import { max, NULL } from "./utils";
 
 const createResizeObserver = (cb: ResizeObserverCallback) => {
   let ro: ResizeObserver | undefined;
@@ -61,7 +61,7 @@ export const createResizer = (
         store._update(ACTION_VIEWPORT_RESIZE, contentRect[sizeKey]);
       } else {
         const index = mountedIndexes.get(target);
-        if (exists(index)) {
+        if (index != NULL) {
           resizes.push([index, contentRect[sizeKey]]);
         }
       }
@@ -112,7 +112,7 @@ export const createWindowResizer = (
       if (!(target as HTMLElement).offsetParent) continue;
 
       const index = mountedIndexes.get(target);
-      if (exists(index)) {
+      if (index != NULL) {
         resizes.push([index, contentRect[sizeKey]]);
       }
     }

src/core/store.ts

@@ -17,7 +17,7 @@ import type {
   ItemResize,
   ItemsRange,
 } from "./types";
-import { abs, max, min } from "./utils";
+import { abs, max, min, NULL } from "./utils";
 
 /** @internal */
 export const SCROLL_IDLE = 0;
@@ -155,7 +155,7 @@ export const createVirtualStore = (
   let _scrollMode: ScrollMode = SCROLL_BY_NATIVE;
   let _frozenRange: ItemsRange | null = isSSR
     ? [0, max(ssrCount - 1, 0)]
-    : null;
+    : NULL;
   let _prevRange: ItemsRange = [0, 0];
   let _totalMeasuredSize = 0;
 
@@ -302,7 +302,7 @@ export const createVirtualStore = (
           // }
 
           if (isSSR) {
-            _frozenRange = null;
+            _frozenRange = NULL;
             isSSR = false;
           }
 
@@ -331,7 +331,7 @@ export const createVirtualStore = (
           }
           _scrollDirection = SCROLL_IDLE;
           _scrollMode = SCROLL_BY_NATIVE;
-          _frozenRange = null;
+          _frozenRange = NULL;
           break;
         }
         case ACTION_ITEM_RESIZE: {

src/core/utils.ts

@@ -1,3 +1,6 @@
+/** @internal */
+export const NULL = null;
+
 /** @internal */
 export const min = Math.min;
 /** @internal */
@@ -20,11 +23,6 @@ export const clamp = (
   maxValue: number
 ): number => min(maxValue, max(minValue, value));
 
-/**
- * @internal
- */
-export const exists = <T>(v: T): v is Exclude<T, null | undefined> => v != null;
-
 /**
  * @internal
  */
@@ -60,14 +58,14 @@ export const debounce = <T extends () => void>(fn: T, ms: number) => {
   let id: ReturnType<typeof setTimeout> | undefined | null;
 
   const cancel = () => {
-    if (exists(id)) {
+    if (id != NULL) {
       clearTimeout(id);
     }
   };
   const debouncedFn = () => {
     cancel();
     id = timeout(() => {
-      id = null;
+      id = NULL;
       fn();
     }, ms);
   };

src/react/ListItem.tsx

@@ -11,6 +11,7 @@ import { ItemResizeObserver } from "../core/resizer";
 import { refKey } from "./utils";
 import { isRTLDocument } from "../core/environment";
 import { CustomItemComponent } from "./types";
+import { NULL } from "../core/utils";
 
 interface ListItemProps {
   _children: ReactNode;
@@ -37,7 +38,7 @@ export const ListItem = memo(
     _isHorizontal: isHorizontal,
     _isSSR: isSSR,
   }: ListItemProps): ReactElement => {
-    const ref = useRef<HTMLDivElement>(null);
+    const ref = useRef<HTMLDivElement>(NULL);
 
     // The index may be changed if elements are inserted to or removed from the start of props.children
     useIsomorphicLayoutEffect(() => resizer(ref[refKey]!, index), [index]);

src/react/VGrid.tsx

@@ -25,6 +25,7 @@ import { ViewportComponentAttributes } from "./types";
 import { flushSync } from "react-dom";
 import { isRTLDocument } from "../core/environment";
 import { useRerender } from "./useRerender";
+import { NULL } from "../core/utils";
 const genKey = (i: number, j: number) => `${i}-${j}`;
 
 /**
@@ -65,7 +66,7 @@ const Cell = memo(
     _hide: hide,
     _element: Element,
   }: CellProps): ReactElement => {
-    const ref = useRef<HTMLDivElement>(null);
+    const ref = useRef<HTMLDivElement>(NULL);
 
     // The index may be changed if elements are inserted to or removed from the start of props.children
     useIsomorphicLayoutEffect(
@@ -249,7 +250,7 @@ export const VGrid = forwardRef<VGridHandle, VGridProps>(
     const hJumpCount = hStore._getJumpCount();
     const height = getScrollSize(vStore);
     const width = getScrollSize(hStore);
-    const rootRef = useRef<HTMLDivElement>(null);
+    const rootRef = useRef<HTMLDivElement>(NULL);
 
     useIsomorphicLayoutEffect(() => {
       const root = rootRef[refKey]!;

src/react/VList.tsx

@@ -5,6 +5,7 @@ import {
   VirtualizerHandle,
   VirtualizerProps,
 } from "./Virtualizer";
+import { NULL } from "../core/utils";
 
 /**
  * Methods of {@link VList}.
@@ -63,7 +64,7 @@ export const VList = forwardRef<VListHandle, VListProps>(
     },
     ref
   ): ReactElement => {
-    const scrollRef = useRef<HTMLDivElement>(null);
+    const scrollRef = useRef<HTMLDivElement>(NULL);
     const shouldReverse = reverse && !horizontal;
 
     let element = (

src/react/Virtualizer.tsx

@@ -30,7 +30,7 @@ import { flushSync } from "react-dom";
 import { useRerender } from "./useRerender";
 import { useChildren } from "./useChildren";
 import { CustomContainerComponent, CustomItemComponent } from "./types";
-import { microtask, sort } from "../core/utils";
+import { microtask, NULL, sort } from "../core/utils";
 
 /**
  * Methods of {@link Virtualizer}.
@@ -194,7 +194,7 @@ export const Virtualizer = forwardRef<VirtualizerHandle, VirtualizerProps>(
 
     const [getElement, count] = useChildren(children, renderCountProp);
 
-    const containerRef = useRef<HTMLDivElement>(null);
+    const containerRef = useRef<HTMLDivElement>(NULL);
 
     const isSSR = useRef(!!ssrCount);
 

src/react/WindowVirtualizer.tsx

@@ -26,6 +26,7 @@ import { ListItem } from "./ListItem";
 import { flushSync } from "react-dom";
 import { useRerender } from "./useRerender";
 import { useChildren } from "./useChildren";
+import { NULL } from "../core/utils";
 
 /**
  * Methods of {@link WindowVirtualizer}.
@@ -138,7 +139,7 @@ export const WindowVirtualizer = forwardRef<
 
     const [getElement, count] = useChildren(children, renderCountProp);
 
-    const containerRef = useRef<HTMLDivElement>(null);
+    const containerRef = useRef<HTMLDivElement>(NULL);
 
     const onScrollEnd = useLatestRef(onScrollEndProp);
 

src/react/utils.ts

@@ -1,5 +1,5 @@
 import { ReactElement, ReactFragment, ReactNode } from "react";
-import { exists, isArray } from "../core/utils";
+import { isArray, NULL } from "../core/utils";
 
 /**
  * @internal
@@ -16,7 +16,7 @@ const forEach = (children: ReactNode, elements: ItemElement[]) => {
     for (const c of children) {
       forEach(c, elements);
     }
-  } else if (!exists(children) || typeof children === "boolean") {
+  } else if (children == NULL || typeof children === "boolean") {
     // filter out, that is the same as React.Children.toArray
   } else {
     elements.push(children);
@@ -49,5 +49,5 @@ type MayHaveKey = { key?: React.Key };
  */
 export const getKey = (e: ItemElement, i: number): React.Key => {
   const key = (e as MayHaveKey).key;
-  return exists(key) ? key : "_" + i;
+  return key != NULL ? key : "_" + i;
 };

src/vue/utils.ts

@@ -1,10 +1,10 @@
 import { VNode } from "vue";
-import { exists } from "../core/utils";
+import { NULL } from "../core/utils";
 
 /**
  * @internal
  */
 export const getKey = (e: VNode, i: number): Exclude<VNode["key"], null> => {
   const key = e.key;
-  return exists(key) ? key : "_" + i;
+  return key != NULL ? key : "_" + i;
 };