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HTML Legend

This example shows how to create a custom HTML legend using a plugin and connect it to the chart in lieu of the default on-canvas legend.

// <block:plugin:0>
const getOrCreateLegendList = (chart, id) => {
  const legendContainer = document.getElementById(id);
  let listContainer = legendContainer.querySelector('ul');

  if (!listContainer) {
    listContainer = document.createElement('ul');
    listContainer.style.display = 'flex';
    listContainer.style.flexDirection = 'row';
    listContainer.style.margin = 0;
    listContainer.style.padding = 0;

    legendContainer.appendChild(listContainer);
  }

  return listContainer;
};

const htmlLegendPlugin = {
  id: 'htmlLegend',
  afterUpdate(chart, args, options) {
    const ul = getOrCreateLegendList(chart, options.containerID);

    // Remove old legend items
    while (ul.firstChild) {
      ul.firstChild.remove();
    }

    // Reuse the built-in legendItems generator
    const items = chart.options.plugins.legend.labels.generateLabels(chart);

    items.forEach(item => {
      const li = document.createElement('li');
      li.style.alignItems = 'center';
      li.style.cursor = 'pointer';
      li.style.display = 'flex';
      li.style.flexDirection = 'row';
      li.style.marginLeft = '10px';

      li.onclick = () => {
        const {type} = chart.config;
        if (type === 'pie' || type === 'doughnut') {
          // Pie and doughnut charts only have a single dataset and visibility is per item
          chart.toggleDataVisibility(item.index);
        } else {
          chart.setDatasetVisibility(item.datasetIndex, !chart.isDatasetVisible(item.datasetIndex));
        }
        chart.update();
      };

      // Color box
      const boxSpan = document.createElement('span');
      boxSpan.style.background = item.fillStyle;
      boxSpan.style.borderColor = item.strokeStyle;
      boxSpan.style.borderWidth = item.lineWidth + 'px';
      boxSpan.style.display = 'inline-block';
      boxSpan.style.height = '20px';
      boxSpan.style.marginRight = '10px';
      boxSpan.style.width = '20px';

      // Text
      const textContainer = document.createElement('p');
      textContainer.style.color = item.fontColor;
      textContainer.style.margin = 0;
      textContainer.style.padding = 0;
      textContainer.style.textDecoration = item.hidden ? 'line-through' : '';

      const text = document.createTextNode(item.text);
      textContainer.appendChild(text);

      li.appendChild(boxSpan);
      li.appendChild(textContainer);
      ul.appendChild(li);
    });
  }
};
// </block:plugin>

// <block:data:1>
const NUM_DATA = 7;
const NUM_CFG = {count: NUM_DATA, min: 0, max: 100};
const data = {
  labels: Utils.months({count: NUM_DATA}),
  datasets: [
    {
      label: 'Dataset: 1',
      data: Utils.numbers(NUM_CFG),
      borderColor: Utils.CHART_COLORS.red,
      backgroundColor: Utils.transparentize(Utils.CHART_COLORS.red, 0.5),
      fill: false,
    },
    {
      label: 'Dataset: 1',
      data: Utils.numbers(NUM_CFG),
      borderColor: Utils.CHART_COLORS.blue,
      backgroundColor: Utils.transparentize(Utils.CHART_COLORS.blue, 0.5),
      fill: false,
    },
  ],
};
// </block:data>

// <block:setup:2>
const config = {
  type: 'line',
  data: data,
  options: {
    plugins: {
      htmlLegend: {
        // ID of the container to put the legend in
        containerID: 'legend-container',
      },
      legend: {
        display: false,
      }
    }
  },
  plugins: [htmlLegendPlugin],
};
// </block:setup>

module.exports = {
  actions: [],
  config: config,
};

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