Builder Pattern #

Composable virtual list — pay only for the features you use.

Why Builder Pattern? #

Different use cases need different features. A contact list doesn't need async loading. A photo gallery doesn't need groups. Bundling everything wastes bytes.

Configuration	Bundle	vs. monolithic
Base (no features)	7.7 KB	–
+ Selection	10.0 KB	2.1× smaller
+ Grid + Scrollbar	11.7 KB	1.8× smaller
+ Groups	12.3 KB	1.8× smaller
+ Async + Page	13.5 KB	1.6× smaller
All features	~16 KB	1.4× smaller

Traditional virtual lists: 20–23 KB minimum (all features bundled).

The Three Steps #

1. `vlist(config)` — create a builder #

import { vlist } from '@floor/vlist';

const builder = vlist({
  container: '#app',
  items: data,
  item: {
    height: 48,
    template: (item) => `<div>${item.name}</div>`,
  },
});
// builder is NOT a list yet

2. `.use(feature)` — add features #

import { withSelection, withScrollbar } from '@floor/vlist';

builder
  .use(withSelection({ mode: 'multiple' }))
  .use(withScrollbar({ autoHide: true }));

Each .use() returns the builder, so calls chain. Features auto-sort by internal priority — you don't need to worry about order.

3. `.build()` — get the instance #

const list = vlist({ ... })
  .use(withSelection({ mode: 'multiple' }))
  .build();

// Now you have a live VList instance
list.scrollToIndex(50);
list.select(1, 2, 3);
list.destroy();

Available Features #

Feature	Import	Cost	Description
`withGrid()`	`@floor/vlist`	+4.0 KB	2D grid layout (virtualises by row)
`withGroups()`	`@floor/vlist`	+4.6 KB	Grouped lists with sticky or inline headers
`withAsync()`	`@floor/vlist`	+5.3 KB	Lazy loading via adapter
`withSelection()`	`@floor/vlist`	+2.3 KB	Single / multiple item selection
`withScale()`	`@floor/vlist`	+2.2 KB	1M+ item compression
`withScrollbar()`	`@floor/vlist`	+1.0 KB	Custom scrollbar UI
`withPage()`	`@floor/vlist`	+0.9 KB	Document-level scrolling
`withSnapshots()`	built-in	0 KB	Scroll save/restore

Feature Compatibility #

Combination	Works?
`withGrid()` + `withGroups()`	✅ Grouped grid
`withGrid()` + `withSelection()`	✅ Selectable gallery
`withGroups()` + `withSelection()`	✅ Selectable grouped list
`withAsync()` + `withScale()`	✅ Large async dataset
`withPage()` + `withAsync()`	✅ Infinite scroll feed
`withGrid()` + `orientation: 'horizontal'`	❌ Grid requires vertical
`withGroups()` + `orientation: 'horizontal'`	❌ Groups require vertical
`withPage()` + `withScrollbar()`	❌ Conflicting scroll ownership
`reverse: true` + `orientation: 'horizontal'`	❌ Reverse requires vertical

The builder throws at runtime if you combine incompatible features.

Complex Example #

File browser with grouped grid, multi-select, and custom scrollbar:

import {
  vlist,
  withGrid,
  withGroups,
  withSelection,
  withScrollbar,
} from '@floor/vlist';

const browser = vlist({
  container: '#browser',
  items: files,
  item: {
    height: 200,
    template: (file, index, { selected }) => `
      <div class="file-card ${selected ? 'file-card--selected' : ''}">
        <img src="${file.thumbnail}" />
        <span>${file.name}</span>
      </div>
    `,
  },
})
  .use(withGrid({ columns: 6, gap: 12 }))
  .use(withGroups({
    getGroupForIndex: (i) => files[i].category,
    headerHeight: 40,
    headerTemplate: (cat) => `<h2 class="category-header">${cat}</h2>`,
    sticky: true,
  }))
  .use(withSelection({ mode: 'multiple' }))
  .use(withScrollbar({ autoHide: true }))
  .build();

// Bundle: ~15.3 KB gzipped

browser.on('selection:change', ({ selectedIds }) => {
  toolbar.setCount(selectedIds.length);
});

Conditional Features #

Features can be added conditionally before calling .build():

import { vlist, withGrid, withSelection } from '@floor/vlist';

let builder = vlist({
  container: '#list',
  items: data,
  item: { height: 200, template: renderItem },
});

if (config.showGrid) {
  builder = builder.use(withGrid({ columns: 4, gap: 16 }));
}
if (config.allowSelection) {
  builder = builder.use(withSelection({ mode: 'multiple' }));
}

const list = builder.build();