JSFiddle - React, Tailwind, and code Playground

HTML

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.12/jquery-ui.min.js"></script>
<link type="text/css" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.12/themes/redmond/jquery-ui.css" rel="stylesheet" />


<div id="showDatepicker"> </div>

<select id="inputdates" name="inputdates" multiple="mulitple"> </select>

CSS

#inputdates
{
    width : 100px;
    height : 150px;
}

JavaScript

$('#showDatepicker').datepicker({
    onSelect: function(dateText, inst) {
        $('#inputdates').append($('<option value=\"' + dateText + '\"></option>').text(dateText));
    },
    beforeShowDay: disableDates
});    


function disableDates(date) {
    var days = daysToDisable();
    for (i = 0; i < days.length; i++) {  
        if ($.inArray(date.toString(), days) != -1) {
            return [false];
        }  
    }
    return [true];  
}

function daysToDisable() {
    var dates = [];
    for (i = 0; i < $('#inputdates option').length; i++) {
        dates[i] = new Date($('#inputdates option').eq(i).val()).toString();
    }
    return dates;
}