JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://code.jquery.com/ui/1.8.19/themes/base/jquery-ui.css">
<div id="calendar"></div>

JavaScript

jQuery(function($) {
    var holidays = {
        4: [1, 2, 3, 4]
    };
    var holidayDetails = {
        4: ["", "May day", "Reason 2", "Another reason","fsdhj"]
    };

    $("#calendar").datepicker({
        defaultDate: "12-05-18",
        dateFormat: 'yy-mm-dd',
        beforeShowDay: checkHoliday
    });

    function checkHoliday(date) {
        day = date.getDate();
        month = date.getMonth();
        isHoliday = $.inArray(day, holidays[month]);
        if (isHoliday >= 0) {
            return [false, '', holidayDetails[month][day]];
        }

        return [true, ''];
    }
});