JSFiddle - React, Tailwind, and code Playground

HTML

<table id="myTable">
    <thead>
        <tr>
            <th class='fc-id1 ui-widget-header'>09:00</th>
        </tr>
        <tr>
            <th class='fc-id2 ui-widget-header'>09:30</th>
        </tr>
        <tr>
            <th class='fc-id3 ui-widget-header'>10:00</th>
        </tr>
    </thead>
    <tbody>
        <tr id='res1'>
            <td class='fc-id4 ui-widget-content fc-resource1'>
                <div class='day-content '></div>
            </td>
        </tr>
        <tr id='res2 '>
            <td class='fc-id5 ui-widget-content fc-resource2 '>
                <div class='day-content'></div>
            </td>
        </tr>
        <tr id='res3'>
            <td class='fc-id6 ui-widget-content fc-resource3'>
                <div class='day-content'></div>
            </td>
        </tr>
    </tbody>
</table>

JavaScript

var id = 3; //from AJAX
var th = $('#myTable th').eq($('.fc-resource'+id).index()).html();
alert(th);