const chart = Highcharts.chart('container', {
    xAxis: {
        categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
        id: 'x-axis'
    },
    subtitle: {
        floating: true,
        align: 'left',
        x: 100,
        y: 70
    },
    series: [{
        data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 54.4]
    }]
});

document.getElementById('button').addEventListener('click', () => {
    chart.setTitle(null, {
        text: 'The axis object: ' + chart.get('x-axis')
    });
});
