Chart.js V2: Add prefix or suffix to tooltip label

Question

In Chart.js V1.0, I would add tooltipTemplate: \"<%if (label){%><%=label %>: <%}%><%= \'€\' + value %>\" to add a euro symbol as prefix

Answer 1

If you have a stacked bar chart (and I assume a stacked line chart) and you want to format all the data points included in a single bar with a currency symbol, you can do something like this:

    tooltips: {
        mode: 'label',
        callbacks: {
            label: function (tooltipItems, data) {
                return '$' + tooltipItems.yLabel;
            }
        }
    },

Note the value of mode.

If you want to have finer control of the tool tip, for example include the labels as they appear the chart's legend, you can do something like this:

    tooltips: {
        mode: 'single',  // this is the Chart.js default, no need to set
        callbacks: {
            label: function (tooltipItems, data) {
                var i, label = [], l = data.datasets.length;
                for (i = 0; i < l; i += 1) {
                    label[i] = data.datasets[i].label + ' : ' + '$' + data.datasets[i].data[tooltipItems.index];
                }
                return label;
            }
        }
    },