JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1/themes/smoothness/jquery-ui.css">
               <div id="tabs">
                    <ul>
                        <li class="tab" id="li1"><a href="#tab-9">tab 9</a></li>
                        <li class="tab" id="li2"><a href="#tab-10">tab 10</a></li>
                        <li class="tab" id="li3"><a href="#tab-21">tab 21</a></li>
                    </ul>
                    <div id="tab-9">
                        tab 9
                    </div>
                   <div id="tab-10">
                        tab 10
                    </div>
                   <div id="tab-21">
                        tab 21
                    </div>
                </div>
            </div>

<br /><br />

<input type="button" id="button" value="get selected" />

JavaScript

$("#tabs").tabs();

$("#button").click(function() {
    var $tabs = $('#tabs').tabs();
    var id = $("li.tab.ui-tabs-selected").attr("id");
    //var id = $("li.tab:not(.ui-tabs-selected)").first().attr("id"); //if you want to fetch an unselected tab         
    alert(id);
});