@surstromming/scroll-area

@surstromming/scroll-area

A scroll container that hides the native scrollbar and paints its own: a step arrow at each end, a draggable thumb, and a track you can page on.

It behaves like a browser's, not like a phone's overlay bar — present whenever there's something to scroll, and then it stays. When the content fits, there's no bar and no gutter: the space comes back.

autoHide swaps that for the overlay behaviour — the bar floats over the content and fades out when idle, appearing on hover, drag or scroll.

Only the painting is ours. The element is a real scroll container, so the wheel, trackpad, keyboard, scrollIntoView and anchor links keep working untouched.

Both axes by default, one bar each, and each bar is there only while its own axis overflows. orientation narrows that — vertical or horizontal forbids the other axis outright — so you reach for it to stop something scrolling, not to ask for a bar.

Dependency graph

graph LR
  scroll_area["@surstromming/scroll-area"]
  design["@surstromming/design"]
  util["@surstromming/util"]
  scroll_area --> design
  scroll_area --> util

Usage

The component brings no height of its own — give it one (or a max-height) and it scrolls what overflows.

<template>
  <ScrollArea :class="$style.box">
    <p v-for="line in lines" :key="line">{{ line }}</p>
  </ScrollArea>
</template>

<script setup lang="ts">
import { ScrollArea } from '@surstromming/scroll-area'

const lines = Array.from({ length: 60 }, (_, index) => `Line ${index + 1}`)
</script>

<style module lang="scss">
.box {
  height: 240px;
}
</style>

Sideways is the same component with no height given to it — the content's own width is what overflows, and the bar's row is all the height it adds:

<ScrollArea>
  <div :class="$style.row">
    <article v-for="card in cards" :key="card.id" :class="$style.card">…</article>
  </div>
</ScrollArea>

The children have to be laid out so they can't wrap — a flex row of flex: 0 0 auto items, or a grid of fixed columns. Nothing here forces that, and content that wraps has nothing to scroll sideways.

orientation only comes up when an axis must be shut off rather than scrolled:

<!-- Long lines are cut, never scrolled; the list still scrolls down. -->
<ScrollArea orientation="vertical" :class="$style.box">…</ScrollArea>

Props

orientation is what the viewport's overflow is set from, both axes always stated: leaving one visible makes the browser promote it to auto, and an axis that scrolls without a bar of ours scrolls behind the hidden native one instead. So vertical really does clip sideways, and horizontal clips vertically — that's the whole reason to pass either. On the default, whichever axes overflow get a bar, and two bars stop short of the corner the other takes.

autoHide also drops the gutter — a bar that comes and goes can't reserve space without the layout jumping — and gives the bar a background wash at 85%, since it now paints over whatever it covers.

Slots

Fallthrough

class, style and listeners land on the root — that's where you set the height. The scrolling element is a private inner div.

Leave display alone, though: the root's grid is what places the bars.

Where it's used

The app's pages are <ScrollArea as="main">, so the whole shell scrolls through it rather than the browser's bar (the .page styles move to an inner div, so padding and max-width stay inside the scroller).

Three components scroll through it too — always, not behind a prop. A boolean every consumer would set to true is noise, and one scrollbar everywhere is the point of having one. Only the consumer's content is wrapped, never their chrome:

Each drops its own overflow and puts its class straight on the ScrollArea root — that root is already the column those classes used to create, so a max-height on it still bounds what scrolls.

The escape hatch isn't a prop either: under forced-colors (Windows high contrast) the painted bar hides itself and the native one comes back. Forced colors replaces the tokens the bar is drawn from, and the OS scrollbar is what the user asked for — so that decision lives here, once, instead of at every call site.

Anatomy

root (grid: 1fr auto / 1fr auto)   ← your height goes here
├── viewport (1/1, overflow per orientation, native bar hidden)
│   └── slot
├── ScrollBar vertical (1/2)       ┐ a track of the grid each — the space one
│   ├── arrow ▲  press and hold to repeat
│   ├── track    click past the thumb to page
│   │   └── thumb  drag to scroll
│   └── arrow ▼                    │ takes *is* its gutter, and the corner cell
└── ScrollBar horizontal (2/1)     ┘ stays empty on its own

A bar that has nothing to scroll collapses to zero across the bar (width: 0 / height: 0) rather than leaving: the grid gives the space straight back, and the track stays measurable, which is what the numbers below are read from. An autoHide bar leaves the grid entirely (position: absolute) and floats.

The gutter is a track and not padding on the viewport, because padding sits at the end of the content: it keeps the last row clear of a bottom bar but lets every row before it scroll underneath. A track shortens the viewport itself.

Each bar is drawn from four measured numbers along its own axis — scroll offset, viewport length, content length, track length. A ResizeObserver watches the viewport, its first child (which is what reports the content's size) and the track, so content that grows re-sizes the thumb.

Tokens

Parked, the bar itself paints nothing — no track fill, no wash. It sits in a track of its own beside the content, so whatever surface it's on shows through and it reads correctly in the sidebar, a popover and a dialog alike. Only autoHide adds the wash, because only then does it cover content.

The carets are a 12×9 inline <svg> triangle, not an icon: a stroked lucide chevron reads as a link affordance at this size and there's no solid caret in the set, so the package doesn't depend on @surstromming/icon. The corners are rounded by stroking the path in its own colour with stroke-linejoin: round — which is also why that colour is opaque, since fill and stroke overlap and a translucent one would draw a darker rim along the edge.

Behaviour

Accessibility

The bar is aria-hidden and its arrows are tabindex="-1": it duplicates scrolling that the viewport already offers to the keyboard, so exposing it twice would only add noise. Screen readers and keyboard users get the native behaviour.