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@jsvision/ui / Slider

Class: Slider ​

Documented in: Slider

Defined in: ui/src/controls/slider.ts:83

A focusable value slider bound two-way to a numeric Signal (see the module docs for glyphs and interaction).

Example ​

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

const caps = resolveCapabilities({ env: {}, platform: 'linux' }).profile;
const green = signal(170);
const slider = at(
  new Slider({
    value: green,
    min: 0,
    max: 255,
    orientation: 'horizontal',
    onInput: (v) => console.log('previewing', v), // live: drag / arrow / wheel
    onChange: (v) => console.log('committed', v), // commit: key step, wheel, pointer-up
  }),
  0,
  0,
  16,
  1,
);

const root = new Group();
root.add(slider);
const loop = createEventLoop({ width: 16, height: 1 }, { caps });
loop.mount(root);
green.set(255); // move externally — the thumb jumps to the far end

Extends ​

Constructors ​

Constructor ​

new Slider(opts): Slider

Defined in: ui/src/controls/slider.ts:103

Parameters ​

opts ​

SliderOptions

The two-way value plus optional min/max/step/pageStep/orientation and the onInput (live) / onChange (commit) callbacks.

Returns ​

Slider

Overrides ​

View.constructor

Properties ​

bounds ​

bounds: Rect

Defined in: ui/src/view/view.ts:66

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

Inherited from ​

View.bounds

castsShadow ​

castsShadow: boolean = false

Defined in: ui/src/view/view.ts:97

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 ​

View.castsShadow

centered ​

centered: boolean = false

Defined in: ui/src/view/view.ts:105

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 ​

View.centered

dragging ​

protected dragging: boolean = false

Defined in: ui/src/controls/slider.ts:97

True while a thumb-drag gesture holds the pointer capture.

focusable ​

focusable: boolean = true

Defined in: ui/src/controls/slider.ts:85

The slider takes focus so its arrow-key stepping is scoped to it.

Overrides ​

View.focusable

grabsFocus ​

grabsFocus: boolean = true

Defined in: ui/src/view/view.ts:122

Whether a mouse-down that hits this view moves keyboard focus to it. Default true — the usual click-to-focus. Set false for a control that should act on a click without stealing focus from whatever is focused (e.g. a dialog Cancel button, or a toolbar/stepper button): the click still dispatches, but the previously-focused view keeps focus, so it never fires a focus-leave side effect such as a field's blur-validation. Independent of focusable — a grabsFocus: false view can still be reached by Tab and activated by Space.

Inherited from ​

View.grabsFocus

layout ​

readonly layout: Readonly<LayoutProps> = {}

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

Layout props for this view (direction, size, padding, absolute placement, …) — read-only.

Change them with setLayout, which is the only writer. The field and every prop on it are closed, so neither view.layout = {…} nor view.layout.rect = {…} compiles, and neither does editing a solved rect a field at a time (view.layout.rect.x = 5). That is deliberate: a wholesale assignment silently drops every prop it omits and never reflows, and an in-place prop write reflows only if you remember to ask.

Read it freely — this is where a view's solved intent lives, and layout.rect is how an absolutely-placed view reports where it was put.

Inherited from ​

View.layout

max ​

protected readonly max: number

Defined in: ui/src/controls/slider.ts:90

min ​

protected readonly min: number

Defined in: ui/src/controls/slider.ts:89

onChange? ​

protected readonly optional onChange?: (v) => void

Defined in: ui/src/controls/slider.ts:95

Parameters ​

v ​

number

Returns ​

void

onInput? ​

protected readonly optional onInput?: (v) => void

Defined in: ui/src/controls/slider.ts:94

Parameters ​

v ​

number

Returns ​

void

pageStepVal ​

protected readonly pageStepVal: number

Defined in: ui/src/controls/slider.ts:92

postProcess ​

postProcess: boolean = false

Defined in: ui/src/view/view.ts:126

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

Inherited from ​

View.postProcess

preProcess ​

preProcess: boolean = false

Defined in: ui/src/view/view.ts:124

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

Inherited from ​

View.preProcess

state ​

readonly state: ViewState

Defined in: ui/src/view/view.ts:75

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

Writing visible or disabled changes only what the next paint would draw — it does not ask for that paint. Follow such a write with invalidate (or invalidateLayout, which a visibility flip needs, since layout omits hidden views). A development build warns when a write goes unaccounted for.

Inherited from ​

View.state

step ​

protected readonly step: number

Defined in: ui/src/controls/slider.ts:91

value ​

protected readonly value: Signal<number>

Defined in: ui/src/controls/slider.ts:88

Two-way numeric value (source of truth).

vertical ​

protected readonly vertical: boolean

Defined in: ui/src/controls/slider.ts:93

Methods ​

accelerators() ​

accelerators(): readonly string[]

Defined in: ui/src/view/view.ts:142

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 ​

View.accelerators

axisLen() ​

protected axisLen(): number

Defined in: ui/src/controls/slider.ts:138

The groove length in cells along the long axis.

Returns ​

number

bind() ​

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

Defined in: ui/src/view/view.ts:326

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 { View, signal, type DrawContext } from '@jsvision/ui';

const count = signal(0);

class StatusLine extends View {
  draw(ctx: DrawContext): void {
    ctx.text(0, 0, `${count()} pending`, ctx.color('statusBar'));
  }
}

const status = new StatusLine();
// In onMount, not the constructor: bind() needs the view's scope, which only exists once mounted.
status.onMount(() => {
  status.bind(() => count()); // repaint the status line whenever `count` changes
});

Inherited from ​

View.bind

commit() ​

protected commit(next): void

Defined in: ui/src/controls/slider.ts:163

Commit a discrete step (key/wheel/select): clamp, and if it changed, fire both onInput and onChange.

Parameters ​

next ​

number

Returns ​

void

derived() ​

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

Defined in: ui/src/view/view.ts:359

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 ​

View.derived

desiredCaret() ​

desiredCaret(): Point | null

Defined in: ui/src/view/view.ts:239

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 ​

View.desiredCaret

draw() ​

draw(ctx): void

Defined in: ui/src/controls/slider.ts:143

Paint the groove, then the thumb cell at the value's mapped offset.

Parameters ​

ctx ​

DrawContext

Returns ​

void

Overrides ​

View.draw

focusSignal() ​

focusSignal(): Signal<void>

Defined in: ui/src/view/view.ts:183

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
import { View, Button, type DrawContext } from '@jsvision/ui';

// A caption that highlights while the control it labels holds focus.
class Caption extends View {
  constructor(
    private readonly text: string,
    private readonly target: View,
  ) {
    super();
    // Reading the target's focus signal inside bind() ties this view's repaint to the target's
    // focus flips — a view can observe focus it does not own.
    this.onMount(() => this.bind(() => this.target.focusSignal()()));
  }

  draw(ctx: DrawContext): void {
    ctx.text(0, 0, this.text, ctx.color(this.target.state.focused ? 'labelSelected' : 'label'));
  }
}

const ok = new Button('~O~K');
const caption = new Caption('Confirm:', ok);

Inherited from ​

View.focusSignal

handleMouse() ​

protected handleMouse(ev): void

Defined in: ui/src/controls/slider.ts:226

Mouse: down positions the thumb (live) and captures the pointer; a drag tracks the pointer live; up commits once and releases the capture — so one drag gesture fires exactly one onChange.

Parameters ​

ev ​

DispatchEvent

The dispatch envelope (carries local plus the pointer-capture seams).

Returns ​

void

invalidate() ​

invalidate(): void

Defined in: ui/src/view/view.ts:244

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

Returns ​

void

Inherited from ​

View.invalidate

invalidateLayout() ​

invalidateLayout(): void

Defined in: ui/src/view/view.ts:250

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

Returns ​

void

Inherited from ​

View.invalidateLayout

live() ​

protected live(next): void

Defined in: ui/src/controls/slider.ts:155

Set the value live (drag/press): clamp, and if it changed, write it and fire onInput only.

Parameters ​

next ​

number

Returns ​

void

measure() ​

measure(): Size2D

Defined in: ui/src/controls/slider.ts:123

Advertise a 1-cell cross axis and a sensible along-axis default for auto sizing.

Returns ​

Size2D

Overrides ​

View.measure

onCleanup() ​

onCleanup(fn): void

Defined in: ui/src/view/view.ts:396

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 ​

View.onCleanup

onEvent() ​

onEvent(ev): void

Defined in: ui/src/controls/slider.ts:177

Route keyboard (along-axis arrows / Home / End / PgUp / PgDn), mouse (click + captured drag), and wheel (step) input. Plain along-axis arrows are consumed so stepping never leaves the slider.

Parameters ​

ev ​

DispatchEvent

The dispatch envelope (carries local plus the pointer-capture seams).

Returns ​

void

Overrides ​

View.onEvent

onMount() ​

onMount(fn): void

Defined in: ui/src/view/view.ts:381

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 ​

View.onMount

readValue() ​

protected readValue(): number

Defined in: ui/src/controls/slider.ts:133

The current value, clamped into [min, max] (a stray external write can't render out of range).

Returns ​

number

select() ​

select(value): void

Defined in: ui/src/controls/slider.ts:128

Programmatically set the value: clamps, then (if it changed) fires both onInput and onChange.

Parameters ​

value ​

number

Returns ​

void

selectByClick()? ​

optional selectByClick(): void

Defined in: ui/src/view/view.ts:229

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 ​

View.selectByClick

setLayout() ​

setLayout(patch): void

Defined in: ui/src/view/view.ts:285

Change some of this view's layout props and request a reflow — the only way to write layout. Props the patch does not name are kept, and the reflow happens for you.

The merge is shallow, deliberately: size and rect are replaced whole rather than merged field-by-field. That is what makes a variant swap correct — going from {kind:'fixed',cells:1} to {kind:'fr',weight:1} must not leave a stale cells behind. The cost is that per-side padding cannot be patched one side at a time; pass the whole padding value.

Two behaviours worth knowing:

  • An explicit undefined resets that prop to its layout default. setLayout({ size: undefined }) makes the view auto-sized again, and setLayout({ position: 'flow' }) puts an absolutely-placed view back in the flow (its now-unused rect is simply ignored).
  • Do not call it in a constructor of a class that subclasses may extend. A base constructor body runs before a subclass's override readonly layout = {…} field initializer, and that initializer installs a fresh object, so the call would be erased. Call it after construction, or from onMount.

Reflowing an unmounted view is a no-op, so calling it before mount is safe.

Parameters ​

patch ​

Partial<LayoutProps>

The layout props to change; anything omitted is preserved.

Returns ​

void

Example ​

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

const panel = new Group();
panel.setLayout({ direction: 'col', padding: 1 });
// Later — `direction` and `padding` survive; once `panel` is mounted this also reflows:
panel.setLayout({ size: { kind: 'fr', weight: 1 } });

Inherited from ​

View.setLayout

valueAt() ​

protected valueAt(localX, localY): number

Defined in: ui/src/controls/slider.ts:249

Map a view-local pointer to the value under it (the along-axis cell → offsetToValue).

Parameters ​

localX ​

number

localY ​

number

Returns ​

number