JSFiddle - React, Tailwind, and code Playground

HTML

<table id="myTable">
    <thead>
        <tr>
            <th class="myHeader">Cat 1</th>
            <th>Vol 1</th>
            <th class="myHeader">Cat 2</th>
            <th>Vol 2</th>
            <th class="myHeader">Cat 3</th>
            <th>Vol 3</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td class="myClass">item1</td>
            <td>8</td>
            <td class="myClass">item2</td>
            <td>7</td>
            <td class="myClass">item1</td>
            <td>2</td>
        </tr>
        <tr>
            <td class="myClass">item3</td>
            <td>5</td>
            <td class="myClass">item2</td>
            <td>7</td>
            <td class="myClass">item2</td>
            <td>4</td>
        </tr>
        <tr>
            <td class="myClass">item3</td>
            <td>1</td>
            <td class="myClass">item1</td>
            <td>5</td>
            <td class="myClass">item3</td>
            <td>3</td>
        </tr>
    </tbody>
</table>

JavaScript

var result = [];

$('#myTable').find('td.myClass').each(function () {
    if ($.inArray($(this).text(), result) == -1) {
        result.push($.trim($(this).text()));
    }
});
console.log(result);