[Chartjs]-How to change ChartJS font size with javascript?

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In ChartJS version 2.7.0 or later, changing (dynamically) the font-size of chart axis’ ticks by just setting the fontSize property of ticks won’t actually apply to the chart. It will only add empty spaces for newly set font-size to the axis’.

In order to change the font-size of chart axis’ ticks properly (which would apply to the chart), you will need to set fontSize property for the minor object (under ticks) , like so :

for (var x in charts) {
   // set/change the actual font-size
   charts[x].options.scales.xAxes[0].ticks.minor.fontSize = 20;
   charts[x].options.scales.yAxes[0].ticks.minor.fontSize = 20;

   // set proper spacing for resized font
   charts[x].options.scales.xAxes[0].ticks.fontSize = 20;
   charts[x].options.scales.yAxes[0].ticks.fontSize = 20;

   // update chart to apply new font-size
   charts[x].update();
}

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var myChart1 = new Chart(ctx1, {
   type: 'line',
   data: {
      labels: ['Jan', 'Feb', 'Mar', 'Apr', 'May'],
      datasets: [{
         label: 'Profit',
         data: [30, 10, 40, 20, 50],
         backgroundColor: 'rgba(61, 208, 239, 0.2)',
         borderColor: 'rgba(61, 208, 239, 0.6)'
      }]
   },
   options: {
      scales: {
         yAxes: [{
            ticks: {
               beginAtZero: true
            }
         }]
      }
   }
});

var myChart2 = new Chart(ctx2, {
   type: 'line',
   data: {
      labels: ['Jan', 'Feb', 'Mar', 'Apr', 'May'],
      datasets: [{
         label: 'Loss',
         data: [50, 20, 40, 10, 30],
         backgroundColor: 'rgba(239, 92, 61, 0.2)',
         borderColor: 'rgba(239, 92, 61, 0.6)'
      }]
   },
   options: {
      scales: {
         yAxes: [{
            ticks: {
               beginAtZero: true
            }
         }]
      }
   }
});

var charts = [myChart1, myChart2];

function changeFontSize() {
   for (var x in charts) {
      // set/change the font-size
      charts[x].options.scales.xAxes[0].ticks.minor.fontSize = 20;
      charts[x].options.scales.yAxes[0].ticks.minor.fontSize = 20;

      // set proper spacing for resized font
      charts[x].options.scales.xAxes[0].ticks.fontSize = 20;
      charts[x].options.scales.yAxes[0].ticks.fontSize = 20;

      // update chart to apply new font-size
      charts[x].update();
   }
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.0/Chart.min.js"></script>

<button onclick="changeFontSize();">Change Font Size</button>
<canvas id="ctx1"></canvas>
<canvas id="ctx2"></canvas>

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