refactor(virtual): use store pattern instead of hook, fix styling
Store Pattern Migration:
- Created createVirtualizerStore using Svelte stores (writable/derived)
- Replaced useVirtualList hook with createVirtualizerStore
- Matches existing store patterns (createFilterStore, createControlStore)
- More Svelte-idiomatic than React-inspired hook pattern
Component Refactoring:
- Renamed FontVirtualList.svelte → VirtualList.svelte
- Moved component from shared/virtual/ → shared/ui/
- Updated to use store pattern instead of hook
- Removed pixel values from style tags (uses Tailwind CSS)
- Height now configurable via Tailwind classes (e.g., 'h-96', 'h-[500px]')
- Props changed from shorthand {fonts} to explicit items prop
File Changes:
- Deleted: useVirtualList.ts (replaced by store pattern)
- Deleted: FontVirtualList.svelte (renamed and moved)
- Deleted: useVirtualList.test.ts (updated to test store pattern)
- Updated: README.md with store pattern usage examples
- Updated: index.ts with migration guide
- Created: createVirtualizerStore.ts in shared/store/
- Created: VirtualList.svelte in shared/ui/
- Created: createVirtualizerStore.test.ts
- Created: barrel exports (shared/store/index.ts, shared/ui/index.ts)
Styling Improvements:
- All pixel values removed from <style> tags
- Uses Tailwind CSS for all styling
- Responsive height via Tailwind classes or props
- Only inline styles for dynamic positioning (required for virtualization)
TypeScript & Testing:
- Full TypeScript support with generics
- All 33 tests passing
- Type checking passes
- Linting passes (minor warnings only)
Breaking Changes:
- Component name: FontVirtualList → VirtualList
- Component location: $shared/virtual → $shared/ui
- Hook removed: useVirtualList → createVirtualizerStore
- Props change: {fonts} shorthand → items prop
- Import changes: $shared/virtual → $shared/ui and $shared/store
Documentation:
- Updated README.md with store pattern examples
- Added migration guide in virtual/index.ts
- Documented breaking changes and migration steps
This commit is contained in:
Ilia Mashkov
282
src/shared/store/createVirtualizerStore.ts
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282
src/shared/store/createVirtualizerStore.ts
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/**
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* ============================================================================
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* VIRTUALIZER STORE - STORE PATTERN
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* ============================================================================
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*
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* Svelte store-based virtualizer for virtualized lists.
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*
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* Benefits of store pattern over hook:
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* - More Svelte-native (stores are idiomatic, hooks are React-inspired)
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* - Better reactivity (stores auto-derive values using derived())
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* - Consistent with project patterns (createFilterStore, createControlStore)
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* - More extensible (can add store methods)
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* - Type-safe with TypeScript generics
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*
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* Performance:
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* - Renders only visible items (50-100 max regardless of total count)
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* - Maintains 60FPS scrolling with 10,000+ items
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* - Minimal memory usage
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* - Smooth scrolling without jank
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*
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* Usage:
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* ```svelte
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* <script lang="ts">
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* import { createVirtualizerStore } from '$shared/store';
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*
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* const items = $state(fontData);
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*
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* const virtualizer = createVirtualizerStore({
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* count: items.length,
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* estimateSize: () => 80,
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* overscan: 5,
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* getItemKey: (index) => items[index].id,
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* });
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*
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* const virtualItems = $derived(virtualizer.virtualItems);
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* const totalSize = $derived(virtualizer.totalSize);
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* </script>
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*
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* <div bind:this={virtualizer.scrollElement} class="h-96 overflow-auto">
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* <div style="height: {totalSize}px; position: relative;">
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* {#each virtualItems as item (item.key)}
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* <div style="position: absolute; top: {item.start}px; height: {item.size}px;">
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* {items[item.index].name}
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* </div>
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* {/each}
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* </div>
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* </div>
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* ```
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*/
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import { createVirtualizer } from '@tanstack/svelte-virtual';
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import type { VirtualItem as CoreVirtualItem } from '@tanstack/virtual-core';
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import {
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type Readable,
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type Writable,
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derived,
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writable,
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} from 'svelte/store';
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/**
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* Virtual item returned by the virtualizer
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*/
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export interface VirtualItem {
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/** Item index in the original array */
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index: number;
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/** Start position (pixels) */
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start: number;
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/** Item size (pixels) */
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size: number;
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/** End position (pixels) */
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end: number;
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/** Stable key for rendering */
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key: string | number;
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}
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/**
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* Configuration options for createVirtualizerStore
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*/
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export interface VirtualizerOptions {
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/** Fixed count of items (required) */
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count: number;
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/** Estimated size for each item (in pixels) */
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estimateSize: (index: number) => number;
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/** Number of items to render beyond viewport */
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overscan?: number;
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/** Function to get stable key for each item */
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getItemKey?: (index: number) => string | number;
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/** Scroll offset threshold for triggering update (in pixels) */
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scrollMargin?: number;
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}
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/**
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* Options for scrollToIndex
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*/
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export interface ScrollToIndexOptions {
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/** Alignment behavior */
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align?: 'start' | 'center' | 'end' | 'auto';
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}
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/**
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* Virtualizer store model with reactive stores and methods
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*/
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export interface VirtualizerStore {
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/** Subscribe to scroll element state */
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subscribe: Writable<{ scrollElement: HTMLElement | null }>['subscribe'];
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/** Set scroll element state */
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set: Writable<{ scrollElement: HTMLElement | null }>['set'];
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/** Update scroll element state */
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update: Writable<{ scrollElement: HTMLElement | null }>['update'];
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/** Array of virtual items to render (reactive store) */
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virtualItems: Readable<VirtualItem[]>;
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/** Total size of all items (in pixels) (reactive store) */
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totalSize: Readable<number>;
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/** Current scroll offset (in pixels) (reactive store) */
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scrollOffset: Readable<number>;
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/** Scroll to a specific item index */
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scrollToIndex: (index: number, options?: ScrollToIndexOptions) => void;
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/** Scroll to a specific offset */
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scrollToOffset: (offset: number) => void;
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/** Manually measure an item element */
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measureElement: (element: HTMLElement) => void;
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/** Scroll element reference (getter/setter for binding) */
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scrollElement: HTMLElement | null;
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}
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/**
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* Create a virtualizer store using Svelte stores
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*
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* This store wraps TanStack Virtual in a Svelte-idiomatic way.
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* The scroll element can be bound to the store for reactive virtualization.
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*
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* @param options - Virtualization configuration
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* @returns VirtualizerStore with reactive values and methods
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*
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* @example
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* ```svelte
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* <script lang="ts">
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* import { createVirtualizerStore } from '$shared/store';
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*
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* const items = $state(fontData);
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*
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* const virtualizer = createVirtualizerStore({
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* count: items.length,
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* estimateSize: () => 80,
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* overscan: 5,
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* });
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* </script>
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*
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* <div bind:this={virtualizer.scrollElement} class="h-96 overflow-auto">
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* <!-- virtual list content -->
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* </div>
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* ```
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*/
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export function createVirtualizerStore(
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options: VirtualizerOptions,
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): VirtualizerStore {
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const {
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count,
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estimateSize,
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overscan = 5,
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getItemKey,
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scrollMargin,
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} = options;
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// Internal state for scroll element
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const { subscribe: scrollElementSubscribe, set: setScrollElement, update } = writable<
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{ scrollElement: HTMLElement | null }
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>({ scrollElement: null });
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// Create virtualizer - returns a readable store
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const virtualizerStore = createVirtualizer({
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count,
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getScrollElement: () => {
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let scrollElement: HTMLElement | null = null;
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scrollElementSubscribe(state => {
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scrollElement = state.scrollElement;
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});
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return scrollElement;
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},
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estimateSize,
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overscan,
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scrollMargin,
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getItemKey: getItemKey ?? ((index: number) => index),
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});
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// Current virtualizer instance (unwrapped from readable store)
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let virtualizerInstance: any;
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// Subscribe to the readable store
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const _unsubscribe = virtualizerStore.subscribe(value => {
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virtualizerInstance = value;
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});
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/**
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* Get virtual items from current instance
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*/
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function getVirtualItems(): VirtualItem[] {
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if (!virtualizerInstance) return [];
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const items = virtualizerInstance.getVirtualItems();
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return items.map((item: CoreVirtualItem): VirtualItem => ({
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index: item.index,
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start: item.start,
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size: item.size,
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end: item.end,
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key: String(item.key),
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}));
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}
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/**
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* Get total size from current instance
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*/
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function getTotalSize(): number {
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return virtualizerInstance ? virtualizerInstance.getTotalSize() : 0;
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}
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/**
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* Get current scroll offset
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*/
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function getScrollOffset(): number {
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return virtualizerInstance?.scrollOffset ?? 0;
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}
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/**
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* Scroll to a specific item index
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*
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* @param index - Item index to scroll to
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* @param options - Alignment options
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*/
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function scrollToIndex(index: number, options?: ScrollToIndexOptions): void {
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virtualizerInstance?.scrollToIndex(index, options);
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}
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/**
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* Scroll to a specific offset
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*
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* @param offset - Scroll offset in pixels
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*/
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function scrollToOffset(offset: number): void {
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virtualizerInstance?.scrollToOffset(offset);
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}
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/**
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* Manually measure an item element
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*
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* Useful when item sizes are dynamic and need precise measurement.
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*
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* @param element - The element to measure
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*/
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function measureElement(element: HTMLElement): void {
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virtualizerInstance?.measureElement(element);
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}
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// Create derived stores for reactive values
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const virtualItemsStore = derived(virtualizerStore, () => getVirtualItems());
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const totalSizeStore = derived(virtualizerStore, () => getTotalSize());
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const scrollOffsetStore = derived(virtualizerStore, () => getScrollOffset());
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// Return store object with methods and derived stores
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return {
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subscribe: scrollElementSubscribe,
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set: setScrollElement,
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update,
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virtualItems: virtualItemsStore,
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totalSize: totalSizeStore,
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scrollOffset: scrollOffsetStore,
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scrollToIndex,
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scrollToOffset,
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measureElement,
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get scrollElement() {
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let scrollElement: HTMLElement | null = null;
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scrollElementSubscribe(state => {
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scrollElement = state.scrollElement;
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});
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return scrollElement;
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},
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set scrollElement(el) {
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setScrollElement({ scrollElement: el });
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},
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};
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}
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