JSFiddle - React, Tailwind, and code Playground

HTML

<table>
  <tbody>
    <tr id="row">
      <td>1</td>
      <td>2</td>
      <td>3</td>
      <td>4</td>
    </tr>
    <tr>
      <td>1</td>
      <td>2</td>
      <td>3</td>
      <td>4</td>
    </tr>
  </tbody>
</table>

JavaScript

$('#row td:nth-child(1)').after('<td>a</td>');