svelte-tiny-virtual-list Svelte Themes

Svelte Tiny Virtual List

📚 A tiny but mighty list virtualization library for Svelte, with zero dependencies 💪 Supports variable heights/widths, sticky items, scrolling to index, and more!

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svelte-tiny-virtual-list

A tiny but mighty list virtualization library, with zero dependencies 💪

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About • Features • Installation • Usage • Examples • License

About

Instead of rendering all your data in a huge list, the virtual list component just renders the items that are visible, keeping your page nice and light.
This is heavily inspired by react-tiny-virtual-list and uses most of its code and functionality!

Features

  • Tiny & dependency free – Only ~5kb gzipped
  • Render millions of items, without breaking a sweat
  • Scroll to index or set the initial scroll offset
  • Supports fixed or variable heights/widths
  • Vertical or Horizontal lists
  • svelte-infinite-loading compatibility

Installation

With npm:

$ npm install svelte-tiny-virtual-list

With yarn:

$ yarn add svelte-tiny-virtual-list

With pnpm:

$ pnpm install svelte-tiny-virtual-list

Usage

<script>
    import VirtualList from 'svelte-tiny-virtual-list';

    const data = ['A', 'B', 'C', 'D', 'E', 'F' /* ... */];
</script>

<VirtualList width="100%" height={600} itemCount={data.length} itemSize={50}>
    {#snippet children({ style, index })}
        <div {style}>
            Letter: {data[index]}, Row: #{index}
        </div>
    {/snippet}
</VirtualList>

Also works pretty well with svelte-infinite-loading:

<script>
    import VirtualList from 'svelte-tiny-virtual-list';
    import InfiniteLoading from 'svelte-infinite-loading';

    let data = $state(['A', 'B', 'C', 'D', 'E', 'F' /* ... */]);

    function infiniteHandler({ detail: { complete, error } }) {
        try {
            // Normally you'd make an http request here...

            const newData = ['G', 'H', 'I', 'J', 'K', 'L' /* ... */];

            data = [...data, ...newData];
            complete();
        } catch (e) {
            error();
        }
    }
</script>

<VirtualList width="100%" height={600} itemCount={data.length} itemSize={50}>
    {#snippet children({ style, index })}
        <div {style}>
            Letter: {data[index]}, Row: #{index}
        </div>
    {/snippet}

    {#snippet footer()}
        <div>
            <InfiniteLoading on:infinite={infiniteHandler} />
        </div>
    {/snippet}
</VirtualList>

Props

Property Type Default Description
width number | string REQUIRED or '100%' Width of the list view box. When scrollDirection is 'horizontal', this property is required to be a number and determines the number of rendered items.
height number | string REQUIRED or '100%' Height of the list view box. When scrollDirection is 'vertical', this property is required to be a number and determines the number of rendered items.
itemCount number REQUIRED The number of items you want to render.
itemSize number | number[] | (index: number) => number REQUIRED Either a fixed height/width (depending on the scrollDirection), an array containing the heights of all the items in your list, or a function that returns the height of an item given its index: (index: number) => number.
scrollDirection 'vertical' | 'horizontal' 'vertical' Whether the list should scroll vertically or horizontally.
scrollOffset number 0 Used to control the scroll offset, but also useful for setting an initial scroll offset.
scrollToIndex number -1 Item index to scroll to (by forcefully scrolling if necessary).
scrollToAlignment 'start' | 'center' | 'end' | 'auto' 'start' Used in combination with scrollToIndex, this prop controls the alignment of the scrolled to item. Use 'auto' to scroll the least amount required to ensure that the specified scrollToIndex item is fully visible.
scrollToBehaviour 'smooth' | 'instant' | 'auto' 'instant' Used in combination with scrollToIndex, this prop controls the behaviour of the scrolling. See: [Element: scroll() method - Web APIs
stickyIndices number[] [] An array of indexes (eg. [0, 10, 25, 30]) to make certain items in the list sticky (position: sticky)
overscanCount number 3 Number of extra buffer items to render above/below the visible items. Tweaking this can help reduce scroll flickering on certain browsers/devices.
estimatedItemSize number 0 Used to estimate the total size of the list before all of its items have actually been measured. The estimated total height is progressively adjusted as items are rendered.
getKey ((index: number) => any) | null undefined Function that returns the key of an item in the list, which is used to uniquely identify an item. This is useful for dynamic data coming from a database or similar. By default, it's using the item's index.
onAfterScroll ({ event: ScrollEvent, offset: number }) => void undefined Function that fires after handling the scroll event. Props: event: ScrollEvent - The original scroll event, offset: number - Either the value of wrapper.scrollTop or wrapper.scrollLeft
onListItemsUpdate ({ start: number, end: number }) => void undefined Function that fires when the visible items are updated. Props: start: number - Index of the first visible item, end: number - Index of the last visible item.

Snippets

  • children - Snippet for each item
    • Prop: { index, style }
      • index: number - Item index
      • style: string - Item style, must be applied to the snippet (look above for example)
  • header - Snippet for the elements that should appear at the top of the list
  • footer - Snippet for the elements that should appear at the bottom of the list (e.g. InfiniteLoading component from svelte-infinite-loading)

Methods

  • recomputeSizes(startIndex: number) - This method force recomputes the item sizes after the specified index (these are normally cached).

VirtualList has no way of knowing when its underlying data has changed, since it only receives a itemSize property. If the itemSize is a number, this isn't an issue, as it can compare before and after values and automatically call recomputeSizes internally. However, if you're passing a function to itemSize, that type of comparison is error prone. In that event, you'll need to call recomputeSizes manually to inform the VirtualList that the size of its items has changed.

Use the methods like this:

<script>
    import { onMount } from 'svelte';
    import VirtualList from 'svelte-tiny-virtual-list';

    const data = ['A', 'B', 'C', 'D', 'E', 'F' /* ... */];

    let virtualList;

    function handleClick() {
        virtualList.recomputeSizes(0);
    }
</script>

<button onclick={handleClick}>Recompute Sizes</button>

<VirtualList
    bind:this={virtualList}
    width="100%"
    height={600}
    itemCount={data.length}
    itemSize={50}
>
    {#snippet children({ style, index })}
        <div {style}>
            Letter: {data[index]}, Row: #{index}
        </div>
    {/snippet}
</VirtualList>

Styling

You can style the elements of the virtual list like this:

<script>
    import VirtualList from 'svelte-tiny-virtual-list';

    const data = ['A', 'B', 'C', 'D', 'E', 'F' /* ... */];
</script>

<div class="list">
    <VirtualList width="100%" height={600} itemCount={data.length} itemSize={50}>
        {#snippet children({ style, index })}
            <div {style}>
                Letter: {data[index]}, Row: #{index}
            </div>
        {/snippet}
    </VirtualList>
</div>

<style>
    .list :global(.virtual-list-wrapper) {
        background-color: #0f0;
        /* ... */
    }

    .list :global(.virtual-list-inner) {
        background-color: #f00;
        /* ... */
    }
</style>

Examples / Demo

License

MIT License

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