JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="datepicker">

JavaScript

var _allowedDates = [
    new Date(2018, 8, 21).getTime(),
    new Date(2018, 8, 22).getTime(),
    new Date(2018, 8, 23).getTime(),
];

function allowedDates(date) {
    date = date.getTime();
    
    for (i in _allowedDates)
        if (date == _allowedDates[i])
            return [true, ""];
    
    return [false, ""];
}

$('#datepicker').datepicker({
    beforeShowDay: allowedDates
});