Lit

@mochart/lit provides lit-html directives for @mochart/core. They work in standalone lit-html templates and inside LitElement render methods alike. Config and data changes get mochart's staged animations for free — axis expansion, value change, axis contraction, and gapless stacked transitions — no extra wiring needed.

Install

npm install @mochart/lit @mochart/core lit-html

The optional stylesheet

If your app uses a global CSS reset (Tailwind's preflight, a normalize.css-style reset), also import the core package's optional stylesheet — it re-asserts the browser defaults the chart's tooltip and message overlays rely on, and never overrides the chart's own styling:

import '@mochart/core/mochart.css';

Quick start

defaultChart is the simplest entry point — give it a raw config and a plain array-of-objects dataset:

import { html, render } from 'lit-html';
import { defaultChart } from '@mochart/lit';

const config = {
  title: { text: 'Revenue' },
  categoryAxis: { property: 'month', type: 'string', scale: 'ordinal' },
  seriesDefaults: { renderer: 'bar' },
  series: [{ property: 'revenue', title: 'Revenue' }]
};

const data = [
  { month: 'Jan', revenue: 10 },
  { month: 'Feb', revenue: 20 }
];

render(html`${defaultChart({ config, data, width: 640, height: 400 })}`, document.body);

chart is the lower-level directive for hosts that manage config enhancement and data providers themselves:

import { enhanceConfig, ArrayOfObjectsDataProvider } from '@mochart/core';
import { chart } from '@mochart/lit';

const mochartConfig = enhanceConfig(config);
const dataProvider = new ArrayOfObjectsDataProvider(data, 'month');

render(html`${chart({ mochartConfig, dataProvider, width: 640, height: 400 })}`, document.body);

Sizing

width and height are optional. The directive renders a container div the chart mounts into; whichever dimension you omit tracks that div's size via ResizeObserver, so you can size the div from surrounding layout and the chart follows it:

html`<div style="width: 100%; height: 400px">${chart({ mochartConfig, dataProvider })}</div>`

The optional className and style props land on the container div itself — the directive equivalent of the class/style fallthrough the component wrappers get (explicit width/height props still win over style):

html`${chart({ mochartConfig, dataProvider, style: 'flex: 1 1 auto; min-width: 0;' })}`

The optional dataTestId prop sets a data-testid attribute on the same container div, for test selectors.

When the data changes

Config and data changes are detected by reference identity: the chart compares the values it receives, not their contents. That matches Lit's own change detection (hasChanged is identity-based too), so the familiar Lit rule applies doubly here — reassign instead of mutate:

// ✓ a new array — Lit re-renders and the chart animates to it
this.data = [...this.data, { month: 'Mar', revenue: 30 }];

// ✗ invisible — same reference: neither Lit nor the chart sees it
this.data.push({ month: 'Mar', revenue: 30 });

The same rule applies to config and to mochartConfig/dataProvider — pass a new object (or provider) to change them.

For hosts that do mutate data in place, the chartRef prop — a callback ref, like Lit's own ref() directive — receives a ChartRef handle with the core refresh() escape hatch. It re-reads the current config/data, re-indexing the built-in providers:

import type { DataRow } from '@mochart/core';
import type { ChartRef } from '@mochart/lit';

private chart: ChartRef | null = null;

render() {
  return html`${defaultChart({
    config,
    data: this.data,
    chartRef: (chart) => { this.chart = chart; }
  })}`;
}

addRow(row: DataRow) {
  this.data.push(row);
  this.chart?.refresh();
}

Callbacks and states

Both directives accept the chart callbacks under their core names (onChartClick, onFocus, onSliceClick, …) and a placeholder prop per state — named *Template rather than *Component, since each takes a lit-html template function rather than a component class. It receives the chart state context (width, height, error, …) and is rendered while the chart is in that state:

const loadingTemplate = ({ width, height }) => html`<div>Loading ${width}x${height}…</div>`;

html`${chart({ mochartConfig, dataProvider, loading, loadingTemplate })}`

Both directives also accept loading and error to force the loading or error state.

Every prop, with its type and its core counterpart, is listed in Framework props.

Controlled state

Focus and legend filtering are chart-managed by default, but each piece of that state has a matching prop that takes over while it is set (not undefined): focusedCategoryIndex (-1 = none), focusedSeriesId and focusedValueAxisId (null = none), and filteredSeriesIds (a map of series id → true = filtered out). Pass back what onFocus and onSeriesFilter report to keep focus and filtering in sync across several charts (the round-trip is shown in Controlled focus and filtering); leave a prop undefined to let the chart keep managing that piece itself.

See it in action

The Lit demo gallery is a full LitElement application built on @mochart/lit; its source lives in packages/mochart-demo-lit.