JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
    </tr>
    <tr>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
    </tr>
</table>

JavaScript

var l1 = $("tr").map(function() { return $(this).children().first(); }).length;
var l2 = $("tr").map(function() { return $(this).children(); }).length;

alert($("tr").children().length);

$("body").append("l1: " + l1).append("<br/> l2: " + l2);