JSFiddle - React, Tailwind, and code Playground

HTML

<table>
<tbody>
   <tr><td class="classone">1234</td></tr>
   <tr><td class="classtwo">1234</td></tr>
   <tr><td class="classthree">1234</td></tr>
</tbody>
</table>


<table>
<tbody>
   <tr><td class="classone">1234</td></tr>
   <tr><td class="classtwo">1234</td></tr>
   <tr><td class="classthree">1234</td></tr>
</tbody>
</table>

JavaScript

function addByClass(classname) {
    var sum = 0;
    $.each($(' ' + classname).replace(/ +/g, '.'), function(i, item) {
        sum += parseInt($(item).html());
    });
    return sum;
}