Chart.js

# 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.
For an html legend to work you need to place an empty div at your web page with the ID you provide in the options to bind to like so: <div id="legend-container"></div>.

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.flexShrink = 0;
      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);
    });
  }
};

# Docs

Last Updated: 2/28/2024, 4:43:58 PM

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