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@jsvision/ui / Scroller

Class: Scroller ​

Documented in: Scroller

Defined in: ui/src/scroll/scroller.ts:68

A scrolling viewport: an oversized content child + auto-owned scroll bar(s) in the reserved edges.

Example ​

ts
import { Scroller, Group, Text, createEventLoop, signal } from '@jsvision/ui';
import { resolveCapabilities } from '@jsvision/core';

const caps = resolveCapabilities({ env: {}, platform: 'linux' }).profile;
const content = new Group();
for (let i = 0; i < 20; i += 1) {
  const line = new Text(`Line ${i + 1}`);
  line.layout = { position: 'absolute', rect: { x: 0, y: i, width: 30, height: 1 } };
  content.add(line);
}
const scroller = new Scroller({ content, extent: { width: 30, height: 20 }, scrollbars: 'vertical' });
scroller.layout = { position: 'absolute', rect: { x: 0, y: 0, width: 24, height: 8 } };

const root = new Group();
root.add(scroller);
const loop = createEventLoop({ width: 24, height: 8 }, { caps });
loop.mount(root);
loop.focusView(scroller);
loop.dispatch({ type: 'key', key: 'pagedown', ctrl: false, alt: false, shift: false }); // reveals lower lines

Extends ​

Constructors ​

Constructor ​

new Scroller(opts): Scroller

Defined in: ui/src/scroll/scroller.ts:95

Parameters ​

opts ​

ScrollerOptions

content + extent (size or thunk) + optional scrollbars mode.

Returns ​

Scroller

Overrides ​

Group.constructor

Properties ​

background? ​

optional background?: keyof Theme

Defined in: ui/src/view/group.ts:64

Optional background theme role filled before children compose, so overlap never leaks cells.

Inherited from ​

Group.background

bounds ​

bounds: Rect

Defined in: ui/src/view/view.ts:65

Parent-relative integer rect; written by the layout pass — read it in draw/hit-testing.

Inherited from ​

Group.bounds

castsShadow ​

castsShadow: boolean = false

Defined in: ui/src/view/view.ts:78

When true, the renderer paints a drop shadow on the cells just below and to the right of this view, in paint order (a later sibling's shadow falls over an earlier one). Default false. The Desktop sets it per window.

Inherited from ​

Group.castsShadow

centered ​

centered: boolean = false

Defined in: ui/src/view/view.ts:86

When true, the layout pass recentres this view within its parent after layout — origin = (parent - self) / 2 on both axes. Intended for absolutely-placed views (a modal dialog, a message box) whose size is fixed and whose origin would otherwise be placed by the caller. Default false; Dialog sets it when centered.

Inherited from ​

Group.centered

children ​

readonly children: View[] = []

Defined in: ui/src/view/group.ts:62

Ordered children; array order is paint order (back-to-front).

Inherited from ​

Group.children

content ​

protected readonly content: View

Defined in: ui/src/scroll/scroller.ts:71

The content view (clipped + offset by -delta).

corner? ​

protected readonly optional corner?: CornerCell

Defined in: ui/src/scroll/scroller.ts:83

The reserved bottom-right corner cell between both bars, present only in 'both' mode.

dx ​

protected readonly dx: Signal<number>

Defined in: ui/src/scroll/scroller.ts:75

Scroll offset on x, shared as the horizontal bar's value.

dy ​

protected readonly dy: Signal<number>

Defined in: ui/src/scroll/scroller.ts:77

Scroll offset on y, shared as the vertical bar's value.

extentOf ​

protected readonly extentOf: () => Size2D

Defined in: ui/src/scroll/scroller.ts:73

The content extent (scroll limit), resolved each draw().

Returns ​

Size2D

focusable ​

focusable: boolean = true

Defined in: ui/src/scroll/scroller.ts:69

Whether this view can receive keyboard focus. Effective focusability also requires the view to be visible and enabled with no hidden/disabled ancestor. Default false; the focus manager drives the state.focused flag.

Overrides ​

Group.focusable

hbar? ​

protected readonly optional hbar?: ScrollBar

Defined in: ui/src/scroll/scroller.ts:81

The owned horizontal bar (bottom row), when the mode includes it.

layout ​

layout: LayoutProps = {}

Defined in: ui/src/view/view.ts:69

Layout props for this view (direction, size, padding, absolute placement, …).

Inherited from ​

Group.layout

maxX ​

protected maxX: number = 0

Defined in: ui/src/scroll/scroller.ts:89

maxY ​

protected maxY: number = 0

Defined in: ui/src/scroll/scroller.ts:90

postProcess ​

postProcess: boolean = false

Defined in: ui/src/view/view.ts:98

Take part in the post-process sweep (after the focused view sees the event).

Inherited from ​

Group.postProcess

preProcess ​

preProcess: boolean = false

Defined in: ui/src/view/view.ts:96

Take part in the pre-process sweep (root→down, before the focused view sees the event).

Inherited from ​

Group.preProcess

state ​

readonly state: ViewState

Defined in: ui/src/view/view.ts:67

Draw-against flags. The object reference is fixed; individual fields mutate (e.g. focused).

Inherited from ​

Group.state

vbar? ​

protected readonly optional vbar?: ScrollBar

Defined in: ui/src/scroll/scroller.ts:79

The owned vertical bar (rightmost column), when the mode includes it.

vpH ​

protected vpH: number = 0

Defined in: ui/src/scroll/scroller.ts:88

vpW ​

protected vpW: number = 0

Defined in: ui/src/scroll/scroller.ts:87

Accessors ​

delta ​

Get Signature ​

get delta(): object

Defined in: ui/src/scroll/scroller.ts:131

The current scroll offset (read-only view of the shared dx/dy signals).

Returns ​

object

x ​

readonly x: number

y ​

readonly y: number

Methods ​

accelerators() ​

accelerators(): readonly string[]

Defined in: ui/src/view/view.ts:114

The Alt+hotkey accelerator characters (lowercase) this view claims in its focus scope, for duplicate-accelerator detection. The base returns none; accelerator-bearing widgets (Button/Label/CheckGroup/RadioGroup) override it to report their ~X~ hotkey(s).

Returns ​

readonly string[]

The claimed accelerator chars, or an empty list when the view claims none.

Inherited from ​

Group.accelerators

add() ​

add(child): void

Defined in: ui/src/view/group.ts:88

Add a child, appending it on top (later in the array draws in front). If this group is already mounted, the child mounts immediately — its scope nested under this group's — and a reflow is scheduled for the new layout; otherwise the child mounts when this group itself mounts.

Parameters ​

child ​

View

The view to append.

Returns ​

void

Inherited from ​

Group.add

addDynamic() ​

addDynamic(build): void

Defined in: ui/src/view/group.ts:135

Add children reactively from a Show/For accessor, so the set of children updates itself as signals change. When the group is mounted, an effect reads the accessor, mounts any newly produced views, unmounts any that disappeared (firing their onCleanup), and schedules a reflow on change. Pass a factory that builds the combinator inside itself, not an already-built accessor — this lets the group own and dispose the combinator's reactive nodes on unmount.

Parameters ​

build ​

DynamicBuilder

A factory that constructs the combinator, e.g. () => Show(cond, then) or () => For(each, key, render).

Returns ​

void

Example ​

ts
import { Group, signal, Show } from '@jsvision/ui';

const open = signal(false);
const group = new Group();
group.addDynamic(() => Show(() => open(), () => new Panel())); // Panel appears when `open` is true

Inherited from ​

Group.addDynamic

bind() ​

bind<T>(reader, apply?, opts?): void

Defined in: ui/src/view/view.ts:228

Bind a reactive value to a redraw. Creates an effect (owned by this view's scope) that reads reader() — subscribing to whatever signals it touches — runs the optional apply(value), then requests a frame: a repaint by default, or a reflow when { relayout: true }. It re-runs automatically whenever those signals change, and is disposed when the view unmounts.

Call it from onMount, not the constructor — the view's scope only exists once mounted, so a pre-mount bind throws rather than silently dropping the binding.

Type Parameters ​

T ​

T

Parameters ​

reader ​

() => T

Reads the reactive source; the signals it reads become dependencies.

apply? ​

(v) => void

Optional: apply the read value to the widget (e.g. store it in a field).

opts? ​

Pass { relayout: true } when the change affects layout, so it reflows instead of just repainting.

relayout? ​

boolean

Returns ​

void

Example ​

ts
import { signal } from '@jsvision/ui';

const count = signal(0);
// `status` is a View whose draw() reads count():
status.onMount(() => {
  status.bind(() => count()); // repaint the status line whenever `count` changes
});

Inherited from ​

Group.bind

derived() ​

protected derived<T>(fn): () => T

Defined in: ui/src/view/view.ts:261

Create a stable derived accessor owned by this view's scope. The returned () => T keeps the same identity for the life of the view, so it is safe to build in the constructor and hand to child views before this view mounts. The backing computed is created lazily under the view's own scope, so it is always owned and disposed at unmount — unlike a bare computed() in the constructor, which would run before any scope exists, leak, and warn.

Reads behave sensibly across the lifecycle:

  • Before mount: evaluates fn() directly (correct current value, nothing persisted). Good for a pre-mount natural-size measure.
  • After mount: builds and memoizes a computed(fn) under the view's scope.
  • After an unmount→remount: the memo is keyed to the scope it was built under, so a remounted view (which gets a fresh scope) re-derives under the new scope instead of returning the previous mount's disposed, now-frozen computed — keeping a Show/For-remounted widget reactive.

Type Parameters ​

T ​

T

Parameters ​

fn ​

() => T

The derivation (pure; the signals it reads become the computed's dependencies).

Returns ​

A stable accessor; call it to read the derived value.

() => T

Inherited from ​

Group.derived

desiredCaret() ​

desiredCaret(): Point | null

Defined in: ui/src/view/view.ts:192

Where this view wants the hardware text cursor, in view-local cells, or null for no cursor (the default — most views never show one). A focused text input overrides this to place the caret at the edit position; the event loop reads it after each frame, converts it to an absolute cell, and moves the terminal cursor there.

Returns ​

Point | null

The view-local caret point (0-based, relative to this view's origin), or null.

Inherited from ​

Group.desiredCaret

draw() ​

draw(ctx): void

Defined in: ui/src/scroll/scroller.ts:143

Position the content + owned bars for the live viewport. Runs on each compose, before the walker descends into the children, so the -delta content offset is applied here rather than through the layout rect (which would clamp negatives to 0). Also re-limits the bars from the current viewport vs extent, so a resize keeps the ranges correct.

Parameters ​

ctx ​

DrawContext

The clipped, view-local paint context (its size is the Scroller's viewport).

Returns ​

void

Overrides ​

Group.draw

focusSignal() ​

focusSignal(): Signal<void>

Defined in: ui/src/view/view.ts:136

Subscribe to this view's focus changes. Reading the returned signal inside a bind/effect re-runs that effect whenever this view gains or loses focus — including from another view (e.g. a Label repainting when the control it labels is focused). The signal notifies on every poke even without a value change. Lazy: the backing signal is created on first call.

Returns ​

Signal<void>

A signal that ticks whenever this view gains or loses focus.

Example ​

ts
// Inside a widget's onMount, repaint whenever `other` view's focus changes:
this.onMount(() => this.bind(() => other.focusSignal()()));

Inherited from ​

Group.focusSignal

handleKey() ​

protected handleKey(k): boolean

Defined in: ui/src/scroll/scroller.ts:187

Map a navigation key to a scroll delta; returns whether it was consumed.

Parameters ​

k ​

string

Returns ​

boolean

invalidate() ​

invalidate(): void

Defined in: ui/src/view/view.ts:197

Request a repaint of this view. A no-op before the view is mounted (the first frame paints everything).

Returns ​

void

Inherited from ​

Group.invalidate

invalidateLayout() ​

invalidateLayout(): void

Defined in: ui/src/view/view.ts:202

Request a reflow (re-run layout, then repaint). Use this when a change affects size/position, not just pixels.

Returns ​

void

Inherited from ​

Group.invalidateLayout

measure()? ​

optional measure(available): Size2D

Defined in: ui/src/view/view.ts:71

Optional intrinsic-size hook for auto sizing — return the size this view wants for available.

Parameters ​

available ​

Size2D

Returns ​

Size2D

Inherited from ​

Group.measure

onCleanup() ​

onCleanup(fn): void

Defined in: ui/src/view/view.ts:298

Register a teardown callback that runs once when this view unmounts. Requires a mounted view — so call it from within onMount. Use it to release anything the view acquired (a timer, an external subscription).

Parameters ​

fn ​

() => void

The teardown callback.

Returns ​

void

Inherited from ​

Group.onCleanup

onEvent() ​

onEvent(ev): void

Defined in: ui/src/scroll/scroller.ts:172

Drive the owned bars from the keyboard + wheel. Arrow = ±1, PgUp/PgDn = ±(viewport−1), Home/End = the extremes, wheel = ±3. All clamped to the viewport limits cached by the last draw().

Parameters ​

ev ​

DispatchEvent

The dispatch envelope.

Returns ​

void

Overrides ​

Group.onEvent

onMount() ​

onMount(fn): void

Defined in: ui/src/view/view.ts:283

Register a callback to run once when the view becomes live (after its first layout gives it bounds). This is where to call bind, since the view's reactive scope exists by then. Registering after the view is already live runs the callback immediately.

Parameters ​

fn ​

() => void

Post-mount setup.

Returns ​

void

Inherited from ​

Group.onMount

remove() ​

remove(child): void

Defined in: ui/src/view/group.ts:104

Remove a child: dispose its scope (recursively disposing its descendants and running their onCleanup), detach it, and schedule a reflow. Removing a non-child (or removing twice) is a safe no-op.

Parameters ​

child ​

View

The view to remove.

Returns ​

void

Inherited from ​

Group.remove

scrollByX() ​

protected scrollByX(d): void

Defined in: ui/src/scroll/scroller.ts:224

Scroll the x axis by d, clamped to [0, maxX].

Parameters ​

d ​

number

Returns ​

void

scrollByY() ​

protected scrollByY(d): void

Defined in: ui/src/scroll/scroller.ts:219

Scroll the y axis by d, clamped to [0, maxY].

Parameters ​

d ​

number

Returns ​

void

selectByClick()? ​

optional selectByClick(): void

Defined in: ui/src/view/view.ts:182

Optional "select + raise on click" hook. Left undefined on the base, so a plain view is not a select/raise target. A container that owns z-order (a Window) overrides it to select and raise itself. The hit-test invokes the first ancestor that defines this — before delivering the mouse-down — so a click always raises the window even if the interior also consumes the click.

Returns ​

void

Inherited from ​

Group.selectByClick