x-chart

A lightweight, zero-dependency SVG chart web component that renders line, bar, and area charts directly from data passed as a JSON attribute or a JS array property. All rendering is imperative SVG; no virtual DOM or framework runtime is involved.

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Tag

<x-chart></x-chart>

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Attributes

Attribute	Type	Default	Description
type	enum string	"line"	Chart type: "line" | "bar" | "area"
data	JSON string	—	Array of series objects (see Data Format section)
height	number	180	Chart height in pixels
padding	number	12	Plot area padding in pixels (applied to all four sides)
grid	boolean	true	Show horizontal grid lines behind the plot
axes	boolean	true	Show x-axis and y-axis tick labels
tooltip	boolean	false	Show a floating tooltip on pointer hover
cursor	enum string	"nearest"	Hit-test strategy: "nearest" | "x" | "none"
disabled	boolean	false	Dims the chart and disables all pointer/keyboard interaction
loading	boolean	false	Replaces chart content with an animated skeleton
selected	string	—	Currently highlighted data point in "seriesId:index" format

Boolean attributes follow the HTML boolean presence convention — the attribute being present (with any value, or empty) means true; absent means false.

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Properties

All properties reflect to their corresponding attributes. Setting a property updates the attribute and triggers a re-render.

Property	Type	Reflects attribute	Notes
type	string	yes	Normalised to one of the allowed enum values
height	number	yes
padding	number	yes
grid	boolean	yes
axes	boolean	yes
tooltip	boolean	yes
cursor	string	yes
disabled	boolean	yes
loading	boolean	yes
selected	string	yes
data	JS array	no	Alternative to the JSON data attribute. Setting this property directly accepts a plain JS array and bypasses JSON parsing. When both the attribute and the property are set, the property takes precedence.

x-format / y-format

The x-format and y-format attributes accept a format spec string that controls how axis tick labels and tooltip values are rendered:

Spec	Example output	Description
"raw"	42.5	Raw value, no transformation (default)
"int"	42	Integer, rounded
"fixed:2"	42.50	Fixed decimal places (N after the colon)
"pct"	42.5%	Percentage suffix
"abbr"	42.5K	Abbreviated with K/M/B suffix

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Data Format

The data attribute accepts a JSON string representing an array of series objects:

[
  {
    "id": "s1",
    "label": "Revenue",
    "color": "#0066cc",
    "data": [
      { "x": 1, "y": 10 },
      { "x": 2, "y": 25 },
      { "x": 3, "y": 18 }
    ]
  },
  {
    "id": "s2",
    "label": "Costs",
    "color": "#cc3300",
    "data": [
      { "x": 1, "y": 5 },
      { "x": 2, "y": 12 },
      { "x": 3, "y": 9 }
    ]
  }
]

Series object fields

Field	Type	Required	Description
id	string	no	Stable identifier used in selected attribute and events. Auto-generated if omitted.
label	string	no	Human-readable series name shown in tooltips and screen-reader announcements.
color	CSS color string	no	Stroke/fill color for this series. Falls back to --x-chart-series-N CSS custom properties in order.
data	{x, y}[]	yes	Array of data points. x may be a number or a category string. y must be numeric.

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Events

Event	Bubbles	Composed	Cancelable	Detail
x-chart-select	yes	yes	no	{ seriesId, index, x, y, value }
x-chart-hover	yes	yes	no	{ seriesId, index, x, y, value }

Event detail fields

Field	Type	Description
seriesId	string	The id of the series that was interacted with
index	number	Zero-based index of the data point within the series
x	number | string	The x value of the data point
y	number	The y value of the data point
value	{x, y}	Full data point object (convenience alias)

x-chart-select fires on pointer click or keyboard activation (Enter/Space) when cursor mode is not "none". It also updates the selected attribute on the element.

x-chart-hover fires on pointer move when tooltip mode is enabled and cursor mode is not "none".

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Parts

Part	Description
container	Outermost div wrapping the SVG. Has tabindex="0" for keyboard focus.
svg	The <svg> element that contains all chart drawing.
sr-only	Visually-hidden region with aria-live="polite" for screen-reader announcements.
tooltip	The floating tooltip card shown on hover when tooltip attribute is set.
tooltip-header	The x-axis label row at the top of the tooltip card.
tooltip-body	Container for the per-series rows.
tooltip-row	One row per series (up to 8 pre-built; hidden rows have data-hidden="true").
tooltip-swatch	Colored dot matching the series color.
tooltip-label	Series label text.
tooltip-value	Formatted y-value, shown right-aligned.

Tooltip behavior

• cursor="x" — tooltip shows one row per series sharing the nearest x position (multi-series mode).
• cursor="nearest" — tooltip shows one row for the single closest data point.
• cursor="none" — tooltip never appears even if the tooltip attribute is set.
• A vertical crosshair line appears at the hovered x position.
• A dot indicator (radius 4 SVG units) appears on each series line at the hovered x.

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CSS Custom Properties

Chart

Variable	Light default	Dark default
--x-chart-series-1	rgba(0,102,204,0.95)	rgba(120,190,255,0.95)
--x-chart-series-2	rgba(16,140,72,0.95)	rgba(80,230,150,0.92)
--x-chart-series-3	rgba(190,20,40,0.95)	rgba(255,100,110,0.93)
--x-chart-series-4	rgba(204,120,0,0.95)	rgba(255,190,60,0.93)
--x-chart-radius	0.75rem	same
--x-chart-border	rgba(0,0,0,0.1)	rgba(255,255,255,0.1)
--x-chart-grid	rgba(0,0,0,0.08)	rgba(255,255,255,0.08)
--x-chart-axis-label	rgba(0,0,0,0.5)	rgba(255,255,255,0.45)
--x-chart-focus-ring	rgba(0,102,204,0.55)	rgba(120,190,255,0.55)

Tooltip

Variable	Light default	Dark default
--x-chart-tooltip-bg	rgba(255,255,255,0.96)	rgba(30,30,35,0.97)
--x-chart-tooltip-border	rgba(0,0,0,0.12)	rgba(255,255,255,0.12)
--x-chart-tooltip-shadow	0 4px 16px …	0 4px 20px …
--x-chart-tooltip-radius	0.5rem	same
--x-chart-tooltip-padding	0.45rem 0.7rem	same
--x-chart-tooltip-font-size	0.8125rem	same
--x-chart-tooltip-header-color	rgba(0,0,0,0.5)	rgba(255,255,255,0.45)
--x-chart-tooltip-label-color	rgba(0,0,0,0.65)	rgba(255,255,255,0.6)
--x-chart-tooltip-value-color	rgba(0,0,0,0.9)	rgba(255,255,255,0.9)
--x-chart-tooltip-swatch-size	8px	same
--x-chart-tooltip-gap	0.35rem	same
--x-chart-crosshair-color	rgba(0,0,0,0.18)	rgba(255,255,255,0.2)
--x-chart-crosshair-width	1	same

Dark mode values are applied automatically via @media (prefers-color-scheme: dark) inside the component's shadow styles. Use these custom properties on the host element to override.

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Accessibility

• [part=container] is a <div> with tabindex="0", making the chart keyboard-focusable.
• When focused, arrow keys move the selection across data points within a series; Tab moves between series.
• The currently selected data point is announced via [part=sr-only] which has role="status" and aria-live="polite".
• Chart SVG elements use <title> and <desc> children for basic SVG accessibility.
• All animations respect @media (prefers-reduced-motion: reduce) — transitions and skeleton animations are disabled when the user has requested reduced motion.
• The disabled attribute sets aria-disabled="true" on the container and removes tabindex.

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Examples

HTML

<!-- Line chart with two series -->
<x-chart
  type="line"
  height="240"
  grid
  axes
  tooltip
  data='[
    {"id":"rev","label":"Revenue","color":"#0066cc","data":[
      {"x":"Jan","y":12},{"x":"Feb","y":19},{"x":"Mar","y":15},
      {"x":"Apr","y":28},{"x":"May","y":34}
    ]},
    {"id":"cost","label":"Costs","color":"#cc2200","data":[
      {"x":"Jan","y":8},{"x":"Feb","y":11},{"x":"Mar","y":9},
      {"x":"Apr","y":14},{"x":"May","y":17}
    ]}
  ]'
></x-chart>

<!-- Bar chart with category x-axis -->
<x-chart
  type="bar"
  height="200"
  grid
  axes
  data='[{"id":"s1","label":"Sales","data":[
    {"x":"Q1","y":42},{"x":"Q2","y":61},{"x":"Q3","y":55},{"x":"Q4","y":78}
  ]}]'
></x-chart>

<!-- Area chart, loading state -->
<x-chart type="area" loading></x-chart>

<!-- Disabled chart -->
<x-chart type="line" disabled data='[{"id":"s1","data":[{"x":1,"y":5}]}]'></x-chart>

Setting data via JS property

const chart = document.querySelector('x-chart');
chart.data = [
  {
    id: 'live',
    label: 'Live feed',
    color: '#0066cc',
    data: Array.from({ length: 20 }, (_, i) => ({ x: i, y: Math.random() * 100 }))
  }
];

Listening to events

const chart = document.querySelector('x-chart');

chart.addEventListener('x-chart-select', e => {
  const { seriesId, index, x, y } = e.detail;
  console.log(`Selected: series=${seriesId}, point=${index}, x=${x}, y=${y}`);
});

chart.addEventListener('x-chart-hover', e => {
  const { seriesId, x, y } = e.detail;
  console.log(`Hovering: series=${seriesId}, x=${x}, y=${y}`);
});

ClojureScript hiccup (reagent-style reference — component is a plain custom element)

[:x-chart
 {:type    "line"
  :height  "240"
  :grid    true
  :axes    true
  :tooltip true
  :data    (js/JSON.stringify
             (clj->js [{:id    "revenue"
                        :label "Revenue"
                        :color "#0066cc"
                        :data  [{:x "Jan" :y 12}
                                {:x "Feb" :y 19}
                                {:x "Mar" :y 15}]}]))}]

CSS custom property overrides

x-chart {
  --x-chart-series-1: #7c3aed;
  --x-chart-series-2: #db2777;
  --x-chart-radius: 6px;
  --x-chart-line-width: 3;
}