Svelte

@mochart/svelte wraps @mochart/core in Svelte 5 components. 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/svelte @mochart/core svelte

Svelte 5 is required (svelte and @mochart/core are peer dependencies); the components are written with runes.

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 dataset — an array of objects or an object of arrays:

<script>
  import { DefaultChart } from '@mochart/svelte';

  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 }
  ];
</script>

<DefaultChart {config} {data} width={640} height={400} />

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

<script>
  import { enhanceConfig, ArrayOfObjectsDataProvider } from '@mochart/core';
  import { Chart } from '@mochart/svelte';

  const mochartConfig = enhanceConfig(config);
  const dataProvider = new ArrayOfObjectsDataProvider(data);
</script>

<Chart {mochartConfig} {dataProvider} width={640} height={400} />

Chart accepts null for mochartConfig and dataProvider while the host is still loading them; pair it with the loading prop to show the loading state until they arrive.

Sizing and the container

width and height are optional. The component renders a container div the chart mounts into; whichever dimension you omit tracks that div's size via ResizeObserver. Size the div with the class/style props and the chart follows it:

<Chart {mochartConfig} {dataProvider} style="width: 100%; height: 400px" />

Explicit width/height props win over conflicting style values.

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 props it receives, not their contents. $state's deep reactivity updates your own markup after an in-place push, but the chart still sees the same array — reassign instead of mutate:

let data = $state(initialData);

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

// ✗ invisible to the chart — same array identity
data.push({ month: 'Mar', revenue: 30 });

The same rule applies to config on DefaultChart and to mochartConfig/dataProvider on Chart — pass a new object (or provider) to change them. A prop change made before the component's first effect run (in a parent's onMount, say) is applied too.

For hosts that do mutate data in place, bind:this exposes a ChartRef handle with the core refresh() escape hatch — it re-reads the current data (the built-in providers read live, so any in-place change is seen):

<script lang="ts">
  import type { DataObject } from '@mochart/core';
  import type { ChartRef } from '@mochart/svelte';

  let chart: ChartRef | undefined = $state();

  function addRow(row: DataObject) {
    data.push(row);
    chart?.refresh();
  }
</script>

<DefaultChart bind:this={chart} {config} {data} />

Callbacks and states

Both components accept the chart callbacks under their core names (onChartClick, onFocus, onSeriesFilter, onSeriesClick, onSliceClick, onTitleClick, …) with the core payloads. Only the callbacks you pass are wired into the chart, which matters where the core switches behavior on a callback's presence — an onTitleClick makes the title a button, for instance.

Both components also accept loading and error to force the loading or error state, and a placeholder prop per state: loadingComponent, errorComponent, noDataComponent, noSizeComponent, noSeriesComponent, and configErrorComponent. Each takes a Svelte component that receives the chart state context (width, height, error, …) as props and is rendered while the chart is in that state; leave a prop off to keep the built-in placeholder.

A placeholder is mounted with a copy of the chart component's contexts, taken when the chart initialises, so getContext inside a placeholder reaches anything an ancestor set with setContext. Contexts are the only thing it inherits: it is mounted as its own component root rather than as a child of the chart. Vue and Angular reach less than this; see Vue and Angular.

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.

TypeScript

The package ships its own declarations. It exports the prop interfaces ChartProps, DefaultChartProps, BaseChartProps (everything except the config/data props) and ChartCallbackProps, the ChartRef handle, and PlaceholderProps/PlaceholderComponent for typing placeholder components. Config, data, and callback payload types (MochartInputConfig, DataObject, ChartFocus, ChartEventPayload, …) come from @mochart/core; see Callbacks and payloads.

Server-side rendering

The chart mounts in onMount, which Svelte does not run on the server: SSR emits only the container div, and the chart is created in the browser after hydration. No browser guards are needed in your own code. Nothing of the chart itself is server-rendered — the page shows an empty container until the client mounts — so a chart contributes no SEO or first-paint content, and a size measured from the container is only known in the browser. See Browser support for what the core itself needs.

See it in action

The Svelte demo gallery is a full application built on @mochart/svelte (with a small history router built on Svelte 5 runes); its source lives in packages/mochart-demo-svelte.