JSFiddle - React, Tailwind, and code Playground

HTML

<table id="data">
<thead>
    <tr><th>Hz</th></tr>
</thead>
    <tbody>
    <tr><td>1</td></tr>
    <tr><td>2</td></tr>
    <tr><td>3</td></tr>
    </tbody>
</table>

JavaScript

var rows1 = document.getElementById("data").rows.length;
var rows2 = document.getElementById("data").getElementsByTagName("tbody")[0].rows.length;

alert(rows1 + "|" + rows2);