Chartjs: how to show only max and min values on y-axis

Question

Using Chart.js, I'd like to display only two labels (or ticks) on the y-axis: the max and min of the values. The values are all floating point numbers.

I'm not sure if the callback function yAxis.ticks.callback is the place to do it.

Answer 1

You can use the following callback function for y-axis ticks to achieve that :

callback: function(value, index, values) {
   if (index === values.length - 1) return Math.min.apply(this, dataArr);
   else if (index === 0) return Math.max.apply(this, dataArr);
   else return '';
}

note: you must use a separate array for data values (here it's dataArr), instead of an in-line one.

EDIT :

add the following in your y-axis ticks config to make the data-points perfectly aligned with the ticks :

min: Math.min.apply(this, dataArr),
max: Math.max.apply(this, dataArr)

---

ᴡᴏʀᴋɪɴɢ ᴇxᴀᴍᴘʟᴇ

var dataArr = [154.23, 203.21, 429.01, 637.41];
var chart = new Chart(ctx, {
   type: 'line',
   data: {
      labels: ['Jan', 'Feb', 'Mar', 'Apr'],
      datasets: [{
         label: 'LINE',
         data: dataArr,
         backgroundColor: 'rgba(0, 119, 290, 0.2)',
         borderColor: 'rgba(0, 119, 290, 0.6)',
         fill: false,
         tension: 0
      }]
   },
   options: {
      scales: {
         yAxes: [{
            ticks: {
               min: Math.min.apply(this, dataArr),
               max: Math.max.apply(this, dataArr),
               callback: function(value, index, values) {
                  if (index === values.length - 1) return Math.min.apply(this, dataArr);
                  else if (index === 0) return Math.max.apply(this, dataArr);
                  else return '';
               }
            }
         }]
      }
   }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script>
<canvas id="ctx"></canvas>