chartjs-plugin-dragdata.js

A plugin for Chart.js that makes data points draggable. Supports touch events & arbitrary Chart.js interaction modes.

Compatible with Chart.js v4, v3 & v2.4+ 🎉

Table of contents

• chartjs-plugin-dragdata.js
  • Table of contents
  • Chart.js version compatibility
  • Online demos
  • Installation
  • npm
  • yarn
  • CDN
  • Getting started
  • Configuration
    • Per-chart configuration
    • Per-scale configuration
    • Per-dataset configuration
    • Per-data-point configuration
  • Example configuration
  • Applying a 'magnet'
  • React integration example
  • Touch devices
  • Gotchas
  • Contributing
  • Additional scripts
  • License

Chart.js version compatibility

Online demos

Click here to learn how to use this plugin in an Observable notebook.

Installation

npm

npm install chartjs-plugin-dragdata

yarn

yarn add chartjs-plugin-dragdata

CDN

In browsers, you may simply add the following script tag:

<script src="https://cdn.jsdelivr.net/npm/chartjs-plugin-dragdata@latest/dist/chartjs-plugin-dragdata.min.js"></script>

Or, download a release archive file from releases.

Getting started

After you install the plugin, it should work out-of-the-box since it features automatic global registration, i.e., automatically calls Chart.register(ChartJSDragDataPlugin) and is therefore applied to all charts. If you want to disable it in a specific chart, please refer to the Configuration section below.

[!NOTE] The automatic registration behaviour is deprecated and is planned to be removed in the nearest major release (v3.0.0). After the change, it will be necessary to perform the registration manually as described in chart.js documentation.

Configuration

The plugin can be configured in multiple ways:

• per-chart (inside plugins section in chart configuration)
• per-scale (inside a scale's configuration)
• per-dataset (inside a dataset's configuration)
• per-data-point (inside a data point's object, for object data points only)

Applying a configuration to disable dragging at any of the above levels will cause the successive (lower on the list) levels to be overridden. For instance, disabling dragging for a dataset will cause all data points inside it to be disabled. This is to achieve compatibility with the previous versions of the library.

[!NOTE] The above is about to change in the nearest major release (v3.0.0). After the change, the configuration of the lower levels will override the higher levels.

Per-chart configuration

Per-chart configuration can be applied to a single chart by adding to chart.options.plugins a property dragData of type PluginConfiguration | boolean.

By default, the plugin is enabled, which is equivalent to setting the property to true. Note that the default behaviour, however, is allowing for dragging only on the y-axis, and not on the x-axis. To enable dragging on the x-axis, you must apply other configuration options. To disable the plugin for a chart, the property must be set to false (which applies just to the given chart).

new Chart(ctx, {
  options: {
    plugins:{
      dragData: ... // PluginConfiguration goes here
    }
  }
})

The PluginConfiguration object can contain the following properties:

Per-scale configuration

Per-scale configuration can be applied to a single chart's scale by adding to chart.options.scales[scaleID] a property dragData of type boolean. This property can be set to true to enable dragging for the entire scale, or to false to disable it.

Per-dataset configuration

Per-dataset configuration can be applied to a single chart's dataset by adding to chart.data.datasets[datasetIndex] a property dragData of type boolean. This property can be set to true to enable dragging for the entire dataset, or to false to disable it.

Per-data-point configuration

Per-data-point configuration can be applied to a single data point by adding to chart.data.datasets[datasetIndex].data[index] a property dragData of type boolean. This property can be set to true to enable dragging for the entire dataset, or to false to disable it.

Example configuration

The following Chart.js sample configuration displays most of the available configuration options of the dragdata plugin. For all of the options, see the Configuration section.

const draggableChart = new Chart(ctx, {
    type: "line",
    data: {
        labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
        datasets: [
            {
                label: "# of Votes",
                data: [12, 19, 3, 5, 2, 3],
                fill: true,
                tension: 0.4,
                borderWidth: 1,
                pointHitRadius: 25, // for improved touch support
                // dragData: false // prohibit dragging this dataset
                // same as returning `false` in the onDragStart callback
                // for this datsets index position
            },
        ],
    },
    options: {
        plugins: {
            dragData: {
                round: 1, // rounds the values to n decimal places
                // in this case 1, e.g 0.1234 => 0.1)
                showTooltip: true, // show the tooltip while dragging [default = true]
                // dragX: true // also enable dragging along the x-axis.
                // this solely works for continous, numerical x-axis scales (no categories or dates)!
                onDragStart: function (event, datasetIndex, index, value) {
                    // you may use this callback to prohibit dragging certain datapoints
                    // by returning false in this callback
                    if (element.datasetIndex === 0 && element.index === 0) {
                        // this would prohibit dragging the first datapoint in the first
                        //dataset entirely
                        return false;
                    }
                },
                onDrag: function (event, datasetIndex, index, value) {
                    // you may control the range in which datapoints are allowed to be
                    // dragged by returning `false` in this callback
                    if (value < 0) return false; // this only allows positive values
                    if (datasetIndex === 0 && index === 0 && value > 20) return false;
                },
                onDragEnd: function (event, datasetIndex, index, value) {
                    // you may use this callback to store the final datapoint value
                    // (after dragging) in a database, or update other UI elements that
                    // dependent on it
                },
            },
        },
        scales: {
            y: {
                dragData: false, // disables datapoint dragging for the entire axis
            },
        },
    },
});

Minimum and maximum allowed data values can also be specified through the min and max ticks settings in the scales options. By setting these values accordingly, unexpected (fast) changes to the scales, that may occur when dragging data points towards the outer boundaries of the y-axis, can be prohibited.

const myChartOptions = {
  type: 'line', // or radar, bar, horizontalBar, bubble
  data: {...},
  options: {
    plugins: {dragData: true},
    scales: {
      y: {
        max: 25,
        min: 0
      }
    }
  }
}

Applying a 'magnet'

In some scenarios, one might want to stop dragging at the closest (rounded) value, or even at a fixed value. This may be achieved by specifying a magnet callback function in the plugins settings:

const myChartOptions = {
  type: 'line', // or radar, bar, bubble
  data: {...},
  options: {
    plugins: {
      dragData: {
        magnet: {
          to: Math.round // to: (value) => value + 5
        }
      }
    }
  }
}

React integration example

You can find a full React example featuring react-chartjs-2 in the repository: chartjs-plugin-dragdata-react-example.

Touch devices

In order to support touch events, the pointHitRadius option should be set to a value greater than 25. You can find working example configurations in the pages/dist-demos/*.html files. Also note, that mobile devices (and thus touch events) can be simulated with the device mode in the Chrome DevTools.

Gotchas

When working with a module bundler (e.g. Rollup/Webpack) and a framework (e.g. Vue.js/React/Angular), you still need to import the plugin library after installing. Here's a small example for a Vue.js component

<template>
  <div>
    <canvas id="chart"></canvas>
  </div>
</template>

<script>
  import { Chart, registerables } from 'chart.js'
  // Load the options file externally for better readability of the component.
  // In the chartOptions object, make sure to add "dragData: true" etc.
  import chartOptions from '~/assets/js/labour.js'
  import 'chartjs-plugin-dragdata'

  export default {
    data() {
      return {
        chartOptions
      }
    },
    mounted() {
      Chart.register(...registerables)
      this.createChart('chart', this.chartOptions)
    },
    methods: {
      createChart(chartId, chartData) {
        const ctx = document.getElementById(chartId)
        const myChart = new Chart(ctx, {
          type: chartData.type,
          data: chartData.data,
          options: chartData.options,
        })
      }
    }
  }
</script>

Contributing

Please feel free to submit an issue or a pull request! If you make changes to the source files, don't forget to:

• npm run build to build the library (outputs will be written to dist/) or npm run build:watch to run the rollup packager in watch mode and build the library each time the source files change
• npm run build:pages or npm run build:pages:watch to build the demo & E2E test pages files; outputs will be written to pages/dist-demos/ for demos, and to /pages/dist-e2e for E2E tests (the latter ones containing eval-using code for injecting data from Playwright)
• run unit, integration & E2E tests with npm run test (or separately with npm run test:unit, npm run test:integration, npm run test:e2e)
• if your changes do change the chart's appearance after performing some interaction, update snapshots by running the command npm run test:e2e:updateSnapshots
• manually test your changes to ensure that they do work and don't break existing features
• when committing, please remember that the commit message must match the conventional commits convention; lefthook will check that for you automatically
• create a PR

Additional scripts

The build command comes in four variants:

• build which builds bundles for all targets:
  • chartjs-plugin-dragdata.esm.js- ESM production, minified (tersed) bundle
  • chartjs-plugin-dragdata.js- UMD production, non-minified bundle
  • chartjs-plugin-dragdata.min.js - UMD production, minified (tersed) bundle
  • chartjs-plugin-dragdata-test.js - bundle for Jest unit tests with coverage instrumentation code injected by rollup-istanbul-plugin
  • chartjs-plugin-dragdata-test-browser.js - bundle for E2E test with additional test-only exports used for automatic tests, allows for injection of urlencoded configuration for Playwright and with coverage instrumentation code injected by rollup-istanbul-plugin
• build:no-coverage which works like build, but does not include the rollup-istanbul-plugin, which may sometimes be helpful when you alter the code and encounter an error when running tests, making the result bundle not contain rubbish code injected by Istanbul
• build:watch which works as build, but watches source files for changes and triggers a rebuild whenever they change
• build:watch:no-coverage which works like a mix of build:watch and build:no-coverage

Scripts for linting are also provided:

• lint which runs ESLint on the project
• lint:fix which runs ESLint on the project in fix mode

License

chartjs-plugin-dragdata.js is available under the MIT license.