chart.js 2.1

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.13.0/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.1.0/Chart.bundle.min.js"></script>
<canvas id="myChart"></canvas>

JavaScript

var d1 = new Date("1945-01-01T00:00:00");
var d2 = new Date("2000-01-01T00:00:00");
var d3 = new Date("2010-01-01T00:00:00");
var datmin = new Date("1940-01-01T00:00:00");
var datmax = Date.now();

var config = {
  type: 'line',
  data: {
    labels: [d1, d2, d3],
    datasets: [{
      label: "Evolution sur la commune",
      data: [200, 100, 90],
      backgroundColor: 'rgba(116, 196, 118, 0.2)',
      borderColor: 'rgba(116, 196, 118, 1)',
      borderWidth: 2
    },
    {
      label: "Moyenne des communes",
      data: [250, 110, 100],
      backgroundColor: 'rgba(200, 200, 200, 0.2)',
      borderColor: 'rgba(200, 200, 200, 1)',
      borderWidth: 2
    }]
  },
  options: {
    showAllTooltips : true,
    scales: {
      xAxes: [{
        type: 'time',
        time: 	{
        	unit: 'year',
          unitStepSize: 10,
          min: datmin,
          max: datmax,
          displayFormats: {'day':'YYYY', 'year': 'YYYY'}
        				}
      				}],
      yAxes: [{
            display: true,
            ticks: {
            		callback: function(label, index, labels) {
        									return label +' m/ha';},
                max: 300,
                min: 0,
                stepSize: 100
            }
        }]
    },
    tooltips: {
      callbacks: {
        label : function (tooltipItems, data) { 
          return tooltipItems.yLabel + ' m/ha';
        },
        title : function (tooltipItem, data) {
        	console.log(data);
        	return tooltipItem[0]["xLabel"].getFullYear();
        }
      }},
  },
};

Chart.pluginService.register({
    beforeRender: function (chart) {
        if (chart.config.options.showAllTooltips) {
            // create an array of tooltips
            // we can't use the chart tooltip because there is only one tooltip per chart
            chart.pluginTooltips = [];
            chart.config.data.datasets.forEach(function (dataset, i) {
                chart.getDatasetMeta(i).data.forEach(function (sector, j) {
            ...