JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://amsul.ca/pickadate.js/vendor/pickadate/lib/picker.js"></script>
<script src="http://amsul.ca/pickadate.js/vendor/pickadate/lib/picker.date.js"></script>
<script src="http://amsul.ca/pickadate.js/vendor/pickadate/lib/picker.time.js"></script>
<link rel="stylesheet" href="http://amsul.ca/pickadate.js/vendor/pickadate/lib/themes/default.css">
<link rel="stylesheet" href="http://amsul.ca/pickadate.js/vendor/pickadate/lib/themes/default.date.css">
<link rel="stylesheet" href="http://amsul.ca/pickadate.js/vendor/pickadate/lib/themes/default.time.css">
<link rel="stylesheet" href="http://amsul.ca/pickadate.js/vendor/pickadate/lib/themes/default.time.css">
Original example:<br/>
<input id="inputDatetime" class="datepicker" type="text" />
<input type="button" id="btn" name="btn" value="disable sundays" />
<input type="button" id="btn2" name="btn2" value="disable mon, tue, sat" />
<br/><br/>
"By the book" example:<br/>
<input id="inputDatetime2" class="datepicker" type="text" />
<input type="button" id="btn3" name="btn3" value="disable fridays" />

JavaScript

$('#inputDatetime').pickadate({
    format: 'dd. mmmm yyyy',
    formatSubmit: 'yyyy-mm-dd',
    selectYears: 2,
    selectMonths: true
});

$('#btn').click(function () {
    disableDates([1]); //sundays
});

$('#btn2').click(function () {
    disableDates([2, 3, 7]); //mondays, tuesdays, saturdays
});

function disableDates(tempValues) {

    var disabledDays = [];

    $.ajax({
        url: '/echo/json/',
        dataType: 'json',
        async: false,
        success: function (data) {
            $.each(tempValues, function (i, d) {
                disabledDays.push(parseInt(tempValues[i]));
            });
        }
    });
    
    console.log(disabledDays);

    var $input = $('#inputDatetime').pickadate();
    var picker = $input.pickadate('picker');

    picker.set({
        disable: disabledDays
    });
}

//-------------- Example 2 ----------------------------------------------------
var myvar = $('#inputDatetime2').pickadate({
    format: 'dd. mmmm yyyy',
    formatSubmit: 'yyyy-mm-dd',
    selectYears: 2,
    selectMonths: true
});

$('#btn3').click(function () {
    disableDates2([6]); //fridays
});

function disableDates2(tempValues) {

    var disabledDays2 = [];

    $.ajax({
        url: '/echo/json/',
        dataType: 'json',
        async: false,
        success: function (data) {
            $.each(tempValues, function (i, d) {
                disabledDays2.push(parseInt(tempValues[i]));
            });
        }
    });
    
    console.log(disabledDays2);

    var picker2 = myvar.pickadate('picker');
    picker2.set('disable', disabledDays2);
}