[Chartjs]-ChartJS Custom text on certain xAxis and yAxis linesS

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You can use the Plugin Core API. It offers different hooks that may be used for executing custom code. In below code snippet, I use the afterDraw hook to draw custom text on the canvas.

For positioning your text on x and y, you may use hard coded number of pixels or compute them using the Scale Interface (i.e. function getPixelForValue).

new Chart(document.getElementById('myChart'), {
  type: 'bar',
  plugins: {
    afterDraw: chart => {
      var ctx = chart.chart.ctx;
      var xAxis = chart.scales['x-axis-0'];
      var yAxis = chart.scales['y-axis-0'];
      ctx.save();
      ctx.font = "18px Arial";
      ctx.fillStyle = "red";
      var x = (xAxis.getPixelForValue('May') + xAxis.getPixelForValue('June')) / 2;
      ctx.fillText('My custom text here', x, yAxis.getPixelForValue(65));
      ctx.fillText('Another custom text here', 30, 15);
      ctx.restore();      
    }
  },
  data: {
    labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
    datasets: [{
      label: "My First Dataset",
      data: [65, 59, 80, 81, 56, 55, 40],
      fill: false,
      backgroundColor: ['rgba(255, 99, 132, 0.2)', 'rgba(255, 159, 64, 0.2)', 'rgba(255, 205, 86, 0.2)', 'rgba(75, 192, 192, 0.2)', 'rgba(54, 162, 235, 0.2)', 'rgba(153, 102, 255, 0.2)', 'rgba(201, 203, 207, 0.2)'],
      borderColor: ['rgb(255, 99, 132)', 'rgb(255, 159, 64)', 'rgb(255, 205, 86)', 'rgb(75, 192, 192)', 'rgb(54, 162, 235)', 'rgb(153, 102, 255)', 'rgb(201, 203, 207)'],
      borderWidth: 1
    }]
  },
  options: {
    scales: {
      yAxes: [{
        ticks: {
          beginAtZero: true
        }
      }]
    }
  }
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.3/Chart.min.js"></script>
<canvas id="myChart" height="110"></canvas>

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