Preact-chartjs-2

Preact wrapper for Chart.js 2 based on the awesome implementation of react-chartjs-2 created by @jerairrest

Open for PRs and contributions!

Demo & Examples

Live demo: bonitasoft.github.io/preact-chartjs-2

To build the examples locally, run:

yarn install
yarn start

Then open localhost:8000 in a browser.

Installation via NPM

yarn add preact-chartjs-2 chart.js

Web Components Compatible

All chart components are exported using skatejs and follow the Custom Elements v1 specs.

Future work:

• Map data and option properties
• Export the full set of components

Usage

Check example/src/components/* for usage.

import {Pie} from 'preact-chartjs-2';

<Pie data={...} />

Properties

• data: (PropTypes.object | PropTypes.func).isRequired,
• width: PropTypes.number,
• height: PropTypes.number,
• legend: PropTypes.object,
• options: PropTypes.object,
• redraw: PropTypes.bool,
• getDatasetAtEvent: PropTypes.func,
• getElementAtEvent: PropTypes.func,
• getElementsAtEvent: PropTypes.func
• onElementsClick: PropTypes.func, // alias for getElementsAtEvent (backward compatibility)

Custom size

In order for Chart.js to obey the custom size you need to set maintainAspectRatio to false, example:

<Bar
  data={data}
  width={100}
  height={50}
  options={{
    maintainAspectRatio: false
  }}
/>

Chart.js instance

Chart.js instance can be accessed by placing a ref to the element as:

render() {
  componentDidMount() {
    console.log(this.refs.chart.chart_instance); // returns a Chart.js instance reference
  }
  return (
    <Doughnut ref='chart' data={data} />
  )
}

Getting context for data generation

Canvas node and hence context, that can be used to create CanvasGradient background, is passed as argument to data if given as function:

This approach is useful when you want to keep your components pure.

render() {
  const data = (canvas) => {
    const ctx = canvas.getContext("2d")
    const gradient = ctx.createLinearGradient(0,0,100,0);
	...
	return {
	  ...
	  backgroundColor: gradient
	  ...
	}
  }

  return (
    <Line data={data} />
  )
}

Chart.js Defaults

Chart.js defaults can be set by importing the defaults object:

import { defaults } from 'preact-chartjs-2';

// Disable animating charts by default.
defaults.global.animation = false;

If you want to bulk set properties, try using the lodash.merge function. This function will do a deep recursive merge preserving previously set values that you don't want to update.

import { defaults } from 'preact-chartjs-2';
import merge from 'lodash.merge';
// or
// import { merge } from 'lodash';

merge(defaults, {
  global: {
      animation: false,
    line: {
      borderColor: '#F85F73',
    },
  },
});

Chart.js object

You can access the internal Chart.js object to register plugins or extend charts like this:

import { Chart } from 'preact-chartjs-2';

componentWillMount() {
  Chart.pluginService.register({
    afterDraw: function (chart, easing) {
      // Plugin code.
    }
  });
}

Scatter Charts

If you're using Chart.js 2.6 and below, add the showLines: false property to your chart options. This was later added in the default config, so users of later versions would not need to do this extra step.

Events

onElementsClick || getElementsAtEvent (function)

A function to be called when mouse clicked on chart elememts, will return all element at that point as an array. Check

{
  onElementsClick: (elems) => {},
  getElementsAtEvent: (elems) => {},
  // `elems` is an array of chartElements
}

getElementAtEvent (function)

Calling getElementAtEvent(event) on your Chart instance passing an argument of an event, or jQuery event, will return the single element at the event position. If there are multiple items within range, only the first is returned Check

{
  getElementAtEvent: (elems) => {},
  // => returns the first element at the event point.
}

getDatasetAtEvent (function)

Looks for the element under the event point, then returns all elements from that dataset. This is used internally for 'dataset' mode highlighting Check

{
  getDatasetAtEvent: (dataset) => {}
  // `dataset` is an array of chartElements
}

Working with Multiple Datasets

You will find that any event which causes the chart to re-render, such as hover tooltips, etc., will cause the first dataset to be copied over to other datasets, causing your lines and bars to merge together. This is because to track changes in the dataset series, the library needs a key to be specified - if none is found, it can't tell the difference between the datasets while updating. To get around this issue, you can take these two approaches:

1. Add a label property on each dataset. By default, this library uses the label property as the key to distinguish datasets.
2. Specify a different property to be used as a key by passing a datasetKeyProvider prop to your chart component, which would return a unique string value for each dataset.

Development (src, lib and the build process)

NOTE: The source code for the component is in src. A transpiled CommonJS version (generated with Babel) is available in lib for use with node.js, browserify and webpack. A UMD bundle is also built to dist, which can be included without the need for any build system.

To build, watch and serve the examples (which will also watch the component source), run npm start. If you just want to watch changes to src and rebuild lib, run npm run watch (this is useful if you are working with npm link).

License

MIT Licensed Copyright (c) Bonitasoft