Year label center alignment with Chart.js

chart_init.js

// Initialization of the Chart using the defined scale type

var labels = [
    '2015-01-01',
    '2015-02-01',
    '2015-03-01',
    '2015-04-01',
    '2015-05-01',
    '2015-06-01',
    // ...continue for 60 months in total for 5 years
];
var data = [
    100,
    110,
    120,
    150,
    130,
    100,
    // ...continue for 60 months in total for 5 years
];
var datasets = [{
    label: 'Data',
    data: data,
    fill: false,
    lineTension: 0,
    pointRadius: 0
}];


var ctx = document.getElementById('#chart').getContext('2d');
var myChart = new Chart(ctx, {
    type: 'line',
    data: {
        labels: labels,
        datasets: datasets
    },
    options: {
        responsive: true,
        maintainAspectRatio: false,
        legend: {
            position: 'top'
        },
        scales: {
            xAxes: [{
                type: 'timecenter',
                time: {
                    unit: 'year',
                    stepSize: 1
                },
                gridLines: {
                    offsetGridLines: true
                },
                maxTicksLimit: 4
            }]
        }
    }
});

scale.timecenter.js

// Relevant part
// Override the getPixelForTick() from the original time scale.
var TimeCenterScale = Chart.scaleService.getScaleConstructor('time').extend({
    getPixelForTick: function(index) {
        var ticks = this.getTicks();
        if (index < 0 || index >= ticks.length) {
            return null;
        }
        // Get the pixel value for the current tick.
        var px = this.getPixelForOffset(ticks[index].value);

        // Get the next tick's pixel value.
        var nextPx = this.right;
        var nextTick = ticks[index + 1];
        if (nextTick) {
            nextPx = this.getPixelForOffset(nextTick.value);
        }

        // Align the labels in the middle of the current and next tick.
        return px + (nextPx - px) / 2;
    },
});
// Register the scale type
var defaults = Chart.scaleService.getScaleDefaults('time');
Chart.scaleService.registerScaleType('timecenter', TimeCenterScale, defaults);