Fountain (Jet d'Eau) API

One chart, two modes: apex height = value, blooming plume = uncertainty. Categorical x = snapshot/comparison; temporal or numeric x = trend - see the Fountain demo.

Import

Web Component

import "@michi-vz/wc/fountain-chart";
// <michi-vz-fountain-chart> is now defined

Vanilla JS

import { mountFountainChart } from "@michi-vz/core";

const chart = mountFountainChart(el, props);

Props

Prop	Type	Default	Description
timeline	boolean | TimelinePeriodConfig	-	Opt-in "play through years" (cumulative): the marks draw UP TO the active period and extend as the timeline steps; `interpolate` sweeps smoothly between years, `false` jump-cuts. Headless controller via `chart.timeline()` plus the built-in play button + scrubber. Off by default; wins over `progressiveDraw` when both are set.
progressiveDraw	boolean | ProgressiveDrawConfig	-	Opt-in reveal animation: wipes the marks in left to right on mount (a clip reveal; axes and titles stay put). `true` uses defaults (1200 ms, easeInOutCubic); a config tunes durationMs, easing, autoplay, and replayOnUpdate (`tipLabel` is LineChart-only and ignored here). Off by default; respects prefers-reduced-motion (renders fully drawn instantly) and `replay()` re-runs it.
dataSet*	FountainDataItem[]	-	Array of jets; each item renders one fountain
title	string	-	Optional chart title rendered above the plot
style	"jet" | "plume"	"jet"	Silhouette style: "jet" (default) is the faithful asymmetric Jet d'Eau (vertical column + wind-blown diagonal + a triangular droplet spray curtain); "plume" is the symmetric blooming column.
xAxisDataType	FountainXAxisType	-	How the x-axis is parsed: a temporal/numeric type renders TREND mode; "band" (or omitted) renders SNAPSHOT mode
yAxisDomain	[number, number]	-	Explicit [min, max] for the value (y) axis; overrides the auto domain from value + spread
xAxisFormat	(d: number | string) => string	-	Formats an x tick value into its display label
yAxisFormat	(d: number | string) => string	-	Formats a y tick value into its display label
ticks	number	5	Approximate number of axis ticks to generate
tickValues	Array<number | Date>	-	Explicit tick values, overriding the generated ones (trend mode)
frothLayers	number	14	Number of graduated-opacity froth layers per jet (default 14, max 20); a per-item density overrides it
bloomExponent	number	5	Exponent in the bloom easing w(h)=stemHalf+spread*(h/H)^p; larger = tighter column, sharper crown (default 5)
stemFraction	number	0.045	Stem half-width at the base as a fraction of the jet's slot width (default 0.045)
showDroplets	boolean	true	Draw ballistic droplet arcs above each apex (default true)
showMist	boolean	true	Draw the misty falling skirt around each nozzle (default true)
showTrendLine	boolean	true	Draw a connecting line through the apexes in trend mode (default true)
tooltipFormatter	(d: FountainDataItem) => string	-	Returns custom tooltip HTML for a hovered jet (sanitized before it is inserted)
onHighlightItem	(labels: string[]) => void	-	Called when the hovered/highlighted label(s) change

Common props - shared by every chart (14)

Prop	Type	Default	Description
width	number	900	Chart width in pixels
height	number	480	Chart height in pixels
margin	Margin	{ top: 50, right: 40, bottom: 50, left: 60 }	Inner margins (top/right/bottom/left, in px); default 8 (36 top with a title)
colors	string[]	-	Categorical palette for rings without an explicit colour or colorsMapping entry
colorsMapping	Record<string, string>	-	Explicit label -> colour map; takes precedence over the palette and per-item colours
highlightItems	string[]	-	Labels to emphasise (active styling); others keep their base opacity
disabledItems	string[]	-	Labels to hide entirely (ring + track removed; remaining rings keep their radii order)
renderer	"svg" | "canvas" | "webgpu"	"svg"	Render as inline SVG (default) or to a canvas / WebGPU layer; getContext() is identical either way
locale	string	-	BCP-47 locale used for number formatting
skipColorMappingDispatch	boolean	false	External-CSS mode: unmapped labels resolve to transparent and onColorMappingGenerated is not emitted, so arc colours come from your CSS via the data-label-safe contract
enableTransitions	boolean	true	Animate opacity/arc changes with CSS transitions (SVG renderer; default true)
onColorMappingGenerated	(mapping: Record<string, string>) => void	-	Called with the resolved label -> colour map after the chart assigns colours
onChartDataProcessed	(context: ChartContext) => void	-	Called with the renderer-agnostic ChartContext whenever the data is (re)processed
onDataWarning	(warnings: DataWarning[]) => void	-	Called with any non-fatal data warnings (out-of-range values, duplicate labels, ...)

Two modes, one data shape

Set xAxisDataType: "band" (or omit it) for Snapshot mode - each item gets its own x-band, side by side. Provide a temporal or numeric xAxisDataType plus a date on each item for Trend mode - the jets are placed along the time axis and a trend line threads their apexes. A predicted: true item renders dashed with a frothier crown.

Events

The web component dispatches these bubbling CustomEvents (the engine exposes the same via the on* callbacks in the table above):

Event	Detail	Fires when
michi-vz:highlight	string[]	hover highlight changes (jet label)
michi-vz:colormapping	Record<string, string>	a color mapping is generated
michi-vz:dataprocessed	ChartContext	data is (re)processed
michi-vz:datawarning	DataWarning[]	input warnings are detected (e.g. non-finite value or spread)

getContext()

mountFountainChart(el, props).getContext() returns a renderer-agnostic FountainChartContext:

• mode - "snapshot" for a categorical/band x, "trend" for a temporal/numeric x.
• jets - one entry per visible jet: { label, code?, color, value, spread, upperBound, spreadRatio, predicted, xPosition }. upperBound = value + spread; spreadRatio = spread / value (relative uncertainty); xPosition is the raw date/number in trend mode, or null in snapshot mode.
• stats - summary object:
  • jetCount - number of visible jets.
  • tallest - { label, value } of the highest jet, or null if empty.
  • frothiest - { label, spreadRatio } of the most uncertain jet, or null if empty.
  • trendSlope - slope of a linear regression through the jet values by index in trend mode; null in snapshot mode.
  • valueRange - [min, max] of the jet values, or null if empty.
  • predictedCount - number of forecast jets.

See LLM context for how to use the context in prompts and reports.

Source

Props are typed as FountainChartProps in @michi-vz/core.