[Chartjs]-ChartJS Version 3 – common legend for multiple line charts

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
          charts.forEach((chartItem) => {
            chartItem.toggleDataVisibility(item.index);
            chartItem.update();
          })
        } else {
          charts.forEach((chartItem) => {
            chartItem.setDatasetVisibility(item.datasetIndex, !chartItem.isDatasetVisible(item.datasetIndex));
            chartItem.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);
    });
  }
};

const options = {
  type: 'line',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets: [{
        label: '# of Votes',
        data: [12, 19, 3, 5, 2, 3],
        borderColor: 'pink',
        backgroundColor: 'pink',
      },
      {
        label: '# of Points',
        data: [7, 11, 5, 8, 3, 7],
        borderColor: 'yellow',
        backgroundColor: 'yellow',
      }
    ]
  },
  options: {
    plugins: {
      legend: {
        display: false,
      },
      htmlLegend: {
        // ID of the container to put the legend in
        containerID: 'chartLegend',
      }
    }
  },
  plugins: [htmlLegendPlugin]
}

const options2 = {
  type: 'line',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets: [{
        label: '# of Votes',
        data: [4, 9, 13, 15, 12, 6],
        borderColor: 'pink',
        backgroundColor: 'pink',
      },
      {
        label: '# of Points',
        data: [17, 1, 15, 18, 9, 3],
        borderColor: 'yellow',
        backgroundColor: 'yellow',
      }
    ]
  },
  options: {
    plugins: {
      legend: {
        display: false
      }
    }
  }
}

const ctx = document.getElementById('chartJSContainer').getContext('2d');
const ctx2 = document.getElementById('chartJSContainer2').getContext('2d');

const chart = new Chart(ctx, options);
const chart2 = new Chart(ctx2, options2);

const charts = [chart, chart2];

<body>
  <div id="chartLegend">

  </div>
  <canvas id="chartJSContainer" width="600" height="400"></canvas>
  <canvas id="chartJSContainer2" width="600" height="400"></canvas>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.5.0/chart.js"></script>
</body>