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<p align="center"><img src="./static/logo.svg" alt="Logo" width="225"></p> <h2 align="center">svelte-tiny-virtual-list</h2> <p align="center">A tiny but mighty list virtualization library, with zero dependencies &#128170;</p> <p align="center"> <a href="https://npmjs.com/package/svelte-tiny-virtual-list"><img src="https://img.shields.io/npm/v/svelte-tiny-virtual-list?style=for-the-badge" alt="NPM VERSION"></a> <a href="https://npmjs.com/package/svelte-tiny-virtual-list"><img src="https://img.shields.io/npm/dt/svelte-tiny-virtual-list?style=for-the-badge" alt="NPM DOWNLOADS"></a> <a href="https://npmjs.com/package/svelte-tiny-virtual-list"><img src="https://img.shields.io/librariesio/release/npm/svelte-tiny-virtual-list?style=for-the-badge" alt="DEPENDENCIES"></a> </p> <p align="center"> <a href="#about">About</a> • <a href="#features">Features</a> • <a href="#installation">Installation</a> • <a href="#usage">Usage</a> • <a href="#examples--demo">Examples</a> • <a href="#license">License</a> </p>

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

Installation

If you're using this component in a Sapper application, make sure to install the package to devDependencies!
More Details

With npm:

$ npm install svelte-tiny-virtual-list

With yarn:

$ yarn add svelte-tiny-virtual-list

With pnpm (recommended):

$ npm i -g pnpm
$ pnpm install svelte-tiny-virtual-list

From CDN (via unpkg):

<!-- UMD -->
<script src="https://unpkg.com/svelte-tiny-virtual-list@^1/dist/svelte-tiny-virtual-list.js"></script>

<!-- ES Module -->
<script src="https://unpkg.com/svelte-tiny-virtual-list@^1/dist/svelte-tiny-virtual-list.mjs"></script>

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}>
	<div slot="item" let:index let:style {style}>
		Letter: {data[index]}, Row: #{index}
	</div>
</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 = ['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}>
	<div slot="item" let:index let:style {style}>
		Letter: {data[index]}, Row: #{index}
	</div>

	<div slot="footer">
		<InfiniteLoading on:infinite={infiniteHandler} />
	</div>
</VirtualList>

Props

PropertyTypeRequired?Description
widthnumber | string*Width of List. This property will determine the number of rendered items when scrollDirection is 'horizontal'.
heightnumber | string*Height of List. This property will determine the number of rendered items when scrollDirection is 'vertical'.
itemCountnumberThe number of items you want to render
itemSizenumber | number[] | (index: number) => numberEither 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
scrollDirectionstringWhether the list should scroll vertically or horizontally. One of 'vertical' (default) or 'horizontal'.
scrollOffsetnumberCan be used to control the scroll offset; Also useful for setting an initial scroll offset
scrollToIndexnumberItem index to scroll to (by forcefully scrolling if necessary)
scrollToAlignmentstringUsed in combination with scrollToIndex, this prop controls the alignment of the scrolled to item. One of: 'start', 'center', 'end' or 'auto'. Use 'start' to always align items to the top of the container and 'end' to align them bottom. Use 'center' to align them in the middle of the container. 'auto' scrolls the least amount possible to ensure that the specified scrollToIndex item is fully visible.
scrollToBehaviourstringUsed in combination with scrollToIndex, this prop controls the behaviour of the scrolling. One of: 'auto', 'smooth' or 'instant' (default).
stickyIndicesnumber[]An array of indexes (eg. [0, 10, 25, 30]) to make certain items in the list sticky (position: sticky)
overscanCountnumberNumber of extra buffer items to render above/below the visible items. Tweaking this can help reduce scroll flickering on certain browsers/devices.
estimatedItemSizenumberUsed 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) => anyFunction 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.

* height must be a number when scrollDirection is 'vertical'. Similarly, width must be a number if scrollDirection is 'horizontal'

Slots

Events

Methods

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 on:click={handleClick}>Recompute Sizes</button>

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