rgjs6-virtual-scroller

v0.3.0-alpha.2

Published

6 months ago

A virtual scroller for the DOM

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rejhgadellaa

RGJS6 Virtual Scroller

A virtual scroller for the DOM, inspired by virtual-scroller.

Getting started

Install via npm:

npm install rgjs6-virtual-scroller

Usage

See https://unpkg.com/rgjs6-virtual-scroller@latest/jsdoc/index.html

HTML:

<!DOCTYPE html>
<html lang="en">
<body>

  <div class="items-container"></div>

</body>
</html>

Javascript:

import VirtualScroller from 'rgjs6-virtual-scroller';

const body = document.body;
const element = document.querySelector('.items-container');

const items = [
  {
    title: 'Item #1',
    subtitle: 'This is the 1st item!',
    href: 'https://www.example.com/',
  },
  // etc...
];

const itemRenderCb = (itemData) => {
  const element = document.createElement('a');
  a.setAttribute('href', itemData.href);
  a.innerHTML = `
    <strong>${itemData.title}</strong><br />
    ${itemData.subtitle}
  `;
  return a;
};

const scroller = new VirtualScroller(element, items, itemRenderCb, {
  viewport: { element: body },
}).init();

Result:

<!DOCTYPE html>
<html lang="en">
<body>

  <div class="items-container">
    <div data-chunk-index="0">
      <a data-item-index="0" href="..."> ... </a>
      <a data-item-index="1" href="..."> ... </a>
      ...
    </div>
    <div data-chunk-index="1">
      <a data-item-index="8" href="..."> ... </a>
      <a data-item-index="9" href="..."> ... </a>
      ...
    </div>
  </div>

</body>
</html>

Overview

Parameters

| Parameter | Type | Default | Description | | --- | --- | --- | --- | | element | HTMLElement | | The container element holding the items | | items | Array | [] | An array of items | | itemRenderCb | Function | null | Called for each item that needs to render. Should return an HTMLElement. | | opts | Object | {} | Options (optional) | | opts.viewport.element | HTMLElement | undefined | If the container is not the scrolling element, you can provide it here | | opts.viewport.rootMarginMode | String | 'auto' | Describes how the Viewport.rootMargin value should be interpreted. Allowed values: 'px|pixel|pixels', '$|percent' or 'auto'. 'auto' causes Viewport.rootMargin to be ignored and automatically sets it to 50% of the height of the viewport. | | opts.viewport.rootMargin | Number | 0 | Similar to how IntersectObserver.rootMargin works. The value is added to the offsetTop of a chunk and used to calculate if an item is in the ViewPort | | opts.chunk.itemsPerChunk | Number | 8 | The number of items a single chunk should contain. | | opts.chunk.keepAlive | Number | 0 | Determines how long a detached chunk should be kept around before allowing garbage collection. 0 means forever. | | opts.item.intrinsicSize | Number | 40 | The assumed size of an item until it's rendered, added to DOM and measured. | | opts.item.keepAlive | Number | 10*1000 | Determines how long a detached item should be kept around before allowing garbage collection. 0 means forever. | | opts.item.cache | Boolean | true | Enables caching an Item's outerHTML for better performance, trading some memory usage. | | opts.debug | Boolean | false | Enables debug output in the console. |

Events

Listen for events using the on() and off() methods, example:

const scroller = new VirtualScroller( /* ... */ )
scroller.on('chunk-change', () => { /* ... */ })
scroller.init();

| Event name | Description | | --- | --- | | 'viewport-resize' | Fired after the viewport size changed and all components have updated.Details: {viewport: Viewport}. | | 'container-resize' | Fired after the container size changed and all components have updated.Details: {container: Container}. | | 'chunk-change' | Fired after chunks was added or removed and all components have updated.Details: {added: [Chunk, ...], removed: [Chunk, ...]}. |

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