Chartjs-How to add an extra tick on top of the highest bar in Chart.js v2.9.4 (grace)?

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You can use a custom plugin to achieve this:

const options = {
  type: 'bar',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
    datasets: [{
        label: '# of Votes',
        data: [12, 20, 3, 5, 2, 3],
        borderWidth: 1
      },
      {
        label: '# of Points',
        data: [7, 11, 5, 8, 3, 7],
        borderWidth: 1
      }
    ]
  },
  options: {
    plugins: {
      customScale: {
        grace: '100%', // Percentage of max value
        // grace: 40 // Flatout extra value to add
      }
    }
  },
  plugins: [{
    id: "customScale",
    beforeLayout: (chart, options, c) => {
      let max = Number.MIN_VALUE;
      let min = Number.MAX_VALUE
      let grace = options.grace || 0

      chart.data.datasets.forEach((dataset) => {
        max = Math.max(max, Math.max(...dataset.data));
        min = Math.min(min, Math.min(...dataset.data))
      })

      if (typeof grace === 'string' && grace.includes('%')) {
        grace = Number(grace.replace('%', '')) / 100

        chart.options.scales.yAxes[0].ticks.suggestedMax = max + (max * grace)
        chart.options.scales.yAxes[0].ticks.suggestedMin = min - (min * grace)

      } else if (typeof grace === 'number') {

        chart.options.scales.yAxes[0].ticks.suggestedMax = max + grace
        chart.options.scales.yAxes[0].ticks.suggestedMin = min - grace

      }

    }
  }]
}

const ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);
<body>
  <canvas id="chartJSContainer" width="600" height="400"></canvas>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.js"></script>
</body>

EDIT:

I assume the ‘BarChart’ is a wrapper component from an external lib in which case you need to pass the plugin to it. I guess it has to be done like so but you might need to check the documentation of the specific wrapper you are using:

<BarChart :data="barChartData" :options="barChartOptions" :plugins="[plugin]" :height="200"/>

const plugin = {
  id: "customScale",
  beforeLayout: (chart, options, c) => {
    let max = Number.MIN_VALUE;
    let min = Number.MAX_VALUE
    let grace = options.grace || 0

    chart.data.datasets.forEach((dataset) => {
      max = Math.max(max, Math.max(...dataset.data));
      min = Math.min(min, Math.min(...dataset.data))
    })

    if (typeof grace === 'string' && grace.includes('%')) {
      grace = Number(grace.replace('%', '')) / 100

      chart.options.scales.yAxes[0].ticks.suggestedMax = max + (max * grace)
      chart.options.scales.yAxes[0].ticks.suggestedMin = min - (min * grace)

    } else if (typeof grace === 'number') {

      chart.options.scales.yAxes[0].ticks.suggestedMax = max + grace
      chart.options.scales.yAxes[0].ticks.suggestedMin = min - grace

    }

  }
}

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