JSFiddle - React, Tailwind, and code Playground

HTML

<table id="data">
    <tr><th>a</th></tr>
    <tr><td>a</td></tr>
    <tr><td>a</td></tr>  
    <tr><td>a</td></tr>  
 </table>

JavaScript

var rows = document.getElementById("data").rows
var count = 0;
for (var i=0; i< rows.length; i++) {
    if (rows[i].cells[0].tagName != 'TH') count++
}
console.log(count)