Slider: stop the track from resizing while you drag#4050
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The text value label sits in the same flex row as the flex-growing track, so a label changing width while dragging resized the track and shifted the thumb under the pointer, retriggering value recalculation. Reserve the width of the widest formatted candidate (min/max/±step, doubled plus separator in range mode) in ch units with tabular-nums so the track size never moves. Also snap decimal steps to the precision of step/min so 0.2 + 0.1 emits 0.3 — not 0.30000000000000004 — in the visible label, aria-valuenow, and onChange. Fixes facebook#4033
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AKnassa
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July 18, 2026 04:28
AKnassa
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July 18, 2026 04:28
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PR Analysis ReportNo new or modified components detected. Bundle Size Summary
Accessibility AuditStatus: No accessibility violations detected. Generated by PR Enrichment workflow | View full report |
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What this does
Fixes the Slider so the bar stays the same size while you drag the knob, and makes the numbers it shows clean (no more
0.30000000000000004).Screen.Recording.2026-07-18.at.12.27.39.AM.mov
Why
The value label next to the slider changed width as the number changed (like "9" becoming "10"), which squeezed the bar, which moved the knob under your mouse, which changed the number again — so the whole thing jittered while dragging. And with decimal steps, the label could show long floating-point garbage.
What changed
aria-valuenow), and in the value given to your code (onChange).How to see it
Open the Slider story in Storybook (
pnpm -F storybook dev, then Core → Slider) and drag the knob back and forth without releasing — the track stays perfectly still and the numbers stay tidy. Six new tests cover the width reservation and the decimal-step precision.Fixes #4033