JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.5/themes/cupertino/jquery-ui.css">
<div id="datepicker"></div>

JavaScript

var dates = [
    [2018, 12, 1],
    [2018, 12, 9],
    [2018, 11, 25]
];

$('#datepicker').datepicker({
    beforeShowDay: function (date){
        var year = date.getFullYear(), month = date.getMonth(), day = date.getDate();
        console.log(year + ' - ' + parseFloat(month+1) + ' - ' + day);
        for (var i=0; i < dates.length; ++i)
            if (year == dates[i][0] && month == dates[i][1] - 1 &&  day == dates[i][2])
                return [false, 'ui-state-highlight ui-state-active'];
        
        return [false];
    }
});