JSFiddle - React, Tailwind, and code Playground

HTML

Select dates to unavaiable
<div id="unvailable"></div>

JavaScript

var unavailableDates = ["19-8-2014","14-8-2014"];

function unavailable(date) {
    dmy = date.getDate() + "-" + (date.getMonth()+1) + "-" +date.getFullYear();
    if ($.inArray(dmy, unavailableDates) < 0) {
        return [true,"","Book Now"];
    } else {
        return [false,"","Booked Out"];
    }
}

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