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Charts

Free

Step Line Chart

A stepped line that holds each month's value flat, then jumps: for counts, prices and plans that change in steps, in Svelte with TanStack Charts.

Framework
Charting library

Preview

Preview width

About

Use it for values that stay put until something changes them: a seat count, a price, a stock level, a status. A sloped line would show a gradual change that never happened; a step shows the jump. For a filled version of the same idea, see the Step Area Chart.

Six monthly values drawn as flat runs joined by vertical jumps, each change halfway between two months. Grid lines sit behind it, the months below, and the tooltip shows the value alone.

Installation

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Usage

<script lang="ts">
import ChartLineStep from "@/components/charts/chart-line-step.svelte";
</script>
<ChartLineStep />

Customize

  • curve: d3Curve(curveStep) draws the steps, changing value halfway between two points. curveStepAfter (from d3-shape) holds a value until the next month and curveStepBefore jumps right after the current one.
  • The rows are { month, desktop }; the stroke is var(--color-desktop), from chartConfig.desktop.
  • Focus and the tooltip snap to each month's point, not to the vertical jumps, so every stop is a real value.
  • Steps read best with few points. With daily data the runs get short; aggregate to weeks or months first.
  • ChartContainer's tooltip passes { hideLabel: true }, so a step shows its value without the month.

FAQ

Where exactly does the line change value?

With curveStep, halfway between two months. Import curveStepAfter from d3-shape (the kit installs it) and pass d3Curve(curveStepAfter) to hold each value until the next month's point, which suits prices and plans that change on a date, or curveStepBefore to jump to the next value right after the current month.

When is a step line better than a sloped one?

When the value can't be in between. A price is $10 until it's $12, a team has 8 seats until it has 10. A sloped line would claim $11 halfway through the month. Keep sloped or curved lines for things that do change gradually, like traffic.

Can I fill the area under the steps?

Use areaY with the same step curve, as the Step Area Chart does. The fill makes the level over time read as an amount.

Why does the tooltip land on the months and not the jumps?

Focus points come from the rows, one per month, at the month's position. The step curve only shapes the path between them, so hovering or pressing the arrow keys always lands on a real reading.

Does it work with daily data?

It works, but the runs get short and the steps blur into a jagged line. Aggregate to weeks or months first, or use the interactive line chart, which is built for ninety days of values.

How does the line's color change in dark mode?

The stroke reads var(--color-desktop), set from chartConfig.desktop, and var(--chart-1) already has a dark value in your theme. For a pair of your own, write theme: { light: "…", dark: "…" } in that entry in place of color.

API Reference

ChartContainer

<div> data-slot="chart"

PropType
configChartConfig

Each series' label, icon and color, read by the tooltip and the legend.

definitionChartDefinition

The chart: defineChart(spec, chartTooltip()), its data, marks, scales and axes, and the tooltip's focus.

ariaLabelstring

The chart's accessible name: the card's title.

ariaDescription?string

The chart's accessible description.

class?string

The container's size: aspect-auto h-[250px] w-full, mx-auto aspect-square max-h-[250px]. It's aspect-video by default.

children?Snippet

What sits under the chart inside the container: a ChartLegend.

tooltip?(ChartTooltipContentOptions & { class?: string }) | false

ChartTooltipContent's options (indicator, hideLabel, labelFormatter…) for the default body, or false for TanStack's own tooltip body.

Type
(ChartTooltipContentOptions & { class?: string }) | false
renderTooltip?Snippet<[ChartTooltipBodySnippetContext]>

A whole tooltip body of your own, in place of ChartTooltipContent: it gets the focused points (each with its datum, group and color). A snippet.

Type
Snippet<[ChartTooltipBodySnippetContext]>
defaultIndex?number

The category whose tooltip shows before any pointer, as Recharts' defaultIndex.

height?number

A fixed height in pixels for the chart, in place of the container's.

aspectRatio?number

A width-to-height ratio for the chart, in place of the container's height.

initialWidth?number

The width the chart renders at before it's measured.

onFocusChange?(point: ChartPoint | null) => void

Called as the focused point changes: a pointer, a key or a tap.

Type
(point: ChartPoint | null) => void
onFocusGroupChange?(points: readonly ChartPoint[]) => void

Called with every point at the focused category (a stacked or grouped chart's).

Type
(points: readonly ChartPoint[]) => void
onSelect?(point: ChartPoint | null) => void

Called when a point is clicked or picked with Enter.

Type
(point: ChartPoint | null) => void
CSS variableType
--color-<key>?color

Each config key's color (its theme color in light and dark), set on the container: the marks paint with var(--color-<key>).

ChartTooltipContent

<div>

PropType
pointsreadonly ChartPoint[]

The focused points, from the tooltip's context. ChartContainer passes them to its default body; a body of your own passes its context's.

indicator?"dot" | "line" | "dashed"

The indicator's shape beside each row.

Type
"dot" | "line" | "dashed"
Default
"dot"
hideLabel?boolean

Hides the label above the rows (the focused category).

Default
false
hideIndicator?boolean

Hides each row's color indicator.

Default
false
label?string

The label's text in place of the focused category, looked up in config.

labelKey?string

The datum field (or config key) the label is read from, looked up in config.

nameKey?string

The datum field (or config key) each row's series is read from: a pie's browser.

valueKey?string

The datum field each row's value is read from, for points that carry geometry rather than values (a pie's, from pie()).

color?string

One indicator color for every row, in place of each series' own.

labelFormatter?(label: string, points: readonly ChartPoint[]) => string

Formats the label (the config's label or the category), with the rows' points: a date written out, a unit.

Type
(label: string, points: readonly ChartPoint[]) => string
formatter?Snippet<[{ index, item, name, value }]>

A row's content in place of its indicator, name and value, as shadcn's formatter: a unit, a currency, a total row. A snippet.

Type
Snippet<[{ index, item, name, value }]>
class?string

Classes for the tooltip's card.

ChartLegend

<div>

PropType
config?ChartConfig

The series to list: the container's config by default.

keys?readonly string[]

The series keys to list, in order: every key with a color by default.

hideIcon?boolean

Hides each series' icon (from config), leaving its color swatch.

Default
false
verticalAlign?"top" | "bottom"

Above the chart or under it.

Type
"top" | "bottom"
Default
"bottom"
class?string

Classes for the legend's row.

ChartConfig

KeyType
label?string

The series' name in the tooltip and the legend.

icon?Component

An icon beside its name in the legend and the tooltip (a lucide-svelte icon).

color?string

Its color in both themes: a token (var(--chart-1)) or any CSS color.

theme?{ light: string; dark: string }

A color for each theme, in place of color.

Helpers

ExportType
chartTooltip?(settings?: ChartTooltipSettings) => ChartDefinitionOptions

defineChart's second argument for a chart with a tooltip: what a pointer or a key focuses (group-x, each category's series, by default), the focus ring, and the host ChartContainer draws its body in.

Type
(settings?: ChartTooltipSettings) => ChartDefinitionOptions
chartTheme?ChartTheme

defineChart's theme in the site's tokens: the text, the grid and the palette (--chart-1 to --chart-5).

chartColors?(config: ChartConfig, keys?: readonly string[]) => { domain: string[]; range: string[] }

defineChart's color: each series key (in config order, or keys') painted var(--color-<key>), for marks with a color channel.

Type
(config: ChartConfig, keys?: readonly string[]) => { domain: string[]; range: string[] }
chartLinearScale?() => LinearScale

A value axis drawn as Recharts draws its default one: zero in the domain, five nice ticks. Pass it as a factory: y: { scale: chartLinearScale }.

Type
() => LinearScale
curveNatural?CurveFactory

D3's natural curve, for a smooth line or area: curve: d3Curve(curveNatural).

curveStep?CurveFactory

D3's step curve, for a line or area that holds each value: curve: d3Curve(curveStep).

curveMonotoneX?CurveFactory

D3's monotone curve, smooth without overshooting a point: curve: d3Curve(curveMonotoneX).

curveLinearClosed?CurveFactory

D3's closed linear curve: a radar's polygon (curve: curveLinearClosed on radialLine and radialArea).

useChart?() => { config: ChartConfig }

The config of the ChartContainer around a component of your own (a custom tooltip body or legend).

Type
() => { config: ChartConfig }
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