Highcharts.stockChart('container', {
    tooltip: {
        formatter() {
            let s = '<b>' + Highcharts.dateFormat('%A, %b %e, %Y', this.x) + '</b>';

            this.points.forEach(point => {
                s += '<br/>1 USD = ' + point.y + ' EUR';
            });

            return s;
        }
    },

    rangeSelector: {
        selected: 1
    },

    series: [{
        name: 'USD to EUR',
        data: usdeur
    }]
});