JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.23/jquery-ui.min.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.7.2/themes/base/jquery-ui.css">
<input type="text" name="foo" />

JavaScript

$(function(){
    $("input").datepicker(
        {
        beforeShowDay: function (date) {
        //getDate() returns the day (0-31)
        if (date.getDate() == 15 || date.getDate() == 1) {
            return [true, ''];
        }
        return [false, ''];
        }
        }
    
    );
});