Slider selects values along a continuum—volumes, zoom levels, time windows, thresholds—where relative position communicates magnitude. Pair a numeric input when precision matters; sliders alone suit exploratory adjustment, not exact compliance thresholds. The mental model is "more or less, and I can feel it by dragging"—not "enter 42".
- Operators benefit from gestural adjustment with immediate feedback (media volume, map zoom proxies, UI density).
- Ranges (
RangeSlider) express min/max filters (time slice, radius, value window) when the bounds are meaningful.
- A value where "about here" is the task, not a specific number.
- Exact legal, contractual, or compliance thresholds—prefer a validated numeric
Input.
- Categorical choices—use
Select or SegmentedControl.
- Values operators commonly paste from spreadsheets—text entry first, slider second.
- Labels include units ("Radius (mi)", "Zoom level"). Localize with
formatMessage. Show min/max anchors when operators need a reference.
- Show the current value near the thumb or in an adjacent field. Precision matters even when dragging.
- Step size. Match the domain's granularity (integer people counts vs. fractional opacity).
- Clamping. Validate text-field edits against the slider's bounds; the two controls should stay in sync.
- Drag side effects. Debounce expensive operations that fire on every drag event. Commit on release when the cost of transient values is high.
- Disabled. Surface the dependency on another setting when it applies.
Do
- Default to safe or neutral values. Show live preview when changing affects media, maps, or layouts.
- Size tracks for touch; thumbs should not be microscopic on tablets.
- Pair the slider with a numeric input when both gesture and precision are needed.
Don't
- Use a slider for binary settings—
Switch communicates on/off clearly.
- Hide the current numeric value when precision matters. Show the number or its input companion.
- Animate value changes so slowly that the operator can't tell if the drag registered.
Thumbs are keyboard operable; announcements for value changes should not spam during drag (consider commit-on-release patterns when noisy); labels and current values are exposed to assistive technology. See Accessibility for the full contract.
