Callout

const config = { type: 'line', data, options: { scales: { y: { beginAtZero: true, max: 140, min: 0 } }, plugins: { annotation: { annotations: { annotation } } } } };

const config = {
  type: 'line',
  data,
  options: {
    scales: {
      y: {
        beginAtZero: true,
        max: 140,
        min: 0
      }
    },
    plugins: {
      annotation: {
        annotations: {
          annotation
        }
      }
    }
  }
};

const annotation = { type: 'label', backgroundColor: 'rgba(245,245,245)', callout: { enabled: true, borderColor: (ctx) => ctx.chart.data.datasets[0].borderColor }, content: (ctx) => 'Maximum value is ' + maxValue(ctx).toFixed(2), font: { size: 16 }, position: { x: (ctx) => maxIndex(ctx) <= 3 ? 'start' : maxIndex(ctx) >= 10 ? 'end' : 'center', y: 'center' }, xAdjust: (ctx) => maxIndex(ctx) <= 3 ? 60 : maxIndex(ctx) >= 10 ? -60 : 0, xValue: (ctx) => maxLabel(ctx), yAdjust: -60, yValue: (ctx) => maxValue(ctx) };

const annotation = {
  type: 'label',
  backgroundColor: 'rgba(245,245,245)',
  callout: {
    enabled: true,
    borderColor: (ctx) => ctx.chart.data.datasets[0].borderColor
  },
  content: (ctx) => 'Maximum value is ' + maxValue(ctx).toFixed(2),
  font: {
    size: 16
  },
  position: {
    x: (ctx) => maxIndex(ctx) <= 3 ? 'start' : maxIndex(ctx) >= 10 ? 'end' : 'center',
    y: 'center'
  },
  xAdjust: (ctx) => maxIndex(ctx) <= 3 ? 60 : maxIndex(ctx) >= 10 ? -60 : 0,
  xValue: (ctx) => maxLabel(ctx),
  yAdjust: -60,
  yValue: (ctx) => maxValue(ctx)
};

const DATA_COUNT = 12; const MIN = 0; const MAX = 100; const numberCfg = {count: DATA_COUNT, min: MIN, max: MAX}; const data = { labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'], datasets: [{ data: Utils.numbers(numberCfg) }] };

const DATA_COUNT = 12;
const MIN = 0;
const MAX = 100;
const numberCfg = {count: DATA_COUNT, min: MIN, max: MAX};
const data = {
  labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'],
  datasets: [{
    data: Utils.numbers(numberCfg)
  }]
};

function maxValue(ctx) { const values = ctx.chart.data.datasets[0].data; return Math.max(...values); } function maxIndex(ctx) { const max = maxValue(ctx); const dataset = ctx.chart.data.datasets[0]; return dataset.data.indexOf(max); } function maxLabel(ctx) { return ctx.chart.data.labels[maxIndex(ctx)]; }

function maxValue(ctx) {
  const values = ctx.chart.data.datasets[0].data;
  return Math.max(...values);
}
function maxIndex(ctx) {
  const max = maxValue(ctx);
  const dataset = ctx.chart.data.datasets[0];
  return dataset.data.indexOf(max);
}
function maxLabel(ctx) {
  return ctx.chart.data.labels[maxIndex(ctx)];
}