ChartJS add tooltip to a grouped bar chart

This can be achieved using the following tooltips label callback function :

tooltips: {
   mode: 'label',
   callbacks: {
      label: function(t, d) {
         var dstLabel = d.datasets[t.datasetIndex].label;
         var yLabel = t.yLabel;
         return dstLabel + ': ' + yLabel + ' €';
      }
   }
}

^{FYI: This has nothing to do with scales. It would work perfectly fine along with scales}

ᴡᴏʀᴋɪɴɢ ᴇxᴀᴍᴘʟᴇ ⧩

var myChart = new Chart(ctx, {
   type: 'bar',
   data: {
      labels: ['Jan', 'Feb', 'Mar', 'Apr', 'May'],
      datasets: [{
         label: 'DST1',
         backgroundColor: '#3e95cd',
         data: [3, 2, 4, 5, 1]
      }, {
         label: 'DST2',
         backgroundColor: '#8e5ea2',
         data: [2, 4, 1, 2, 5]
      }]
   },
   options: {
      scales: {
         yAxes: [{
            ticks: {
               beginAtZero: true,
               stepSize: 1
            }
         }]
      },
      title: {
         display: true,
         text: 'Title'
      },
      tooltips: {
         mode: 'label',
         callbacks: {
            label: function(t, d) {
               var dstLabel = d.datasets[t.datasetIndex].label;
               var yLabel = t.yLabel;
               return dstLabel + ': ' + yLabel + ' €';
            }
         }
      }
   }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.1/Chart.js"></script>
<canvas id="ctx"></canvas>

A bit late to the party, but I have recently discovered JavaScript's built-in formatter for currencies, that saves you having to play about with strings and could be helpful here, and is reusable elsewhere in your code!:

const gbp = new Intl.NumberFormat('en-GB', {
    style: 'currency',
    currency: 'GBP',
    minimumFractionDigits: 2
});

Being English I have of course done it in GBP, but I found that changing the en-GB to de-DE and the 'GBP' to 'EUR' worked absolutely fine. Even formatting the decimal points and thousand separators correctly.

EDIT: including how to actually give the formatter a number to format would be useful wouldn't it!

gbp.format(10000); // Returns £10,000.00