JSFiddle - React, Tailwind, and code Playground

by jfriend00

HTML

<table border="0" cellspacing="5" cellpadding="5" id="tbl">
        <tr><th>Header</th></tr>
        <tr><td>Data 1</td></tr>
        <tr><td>Data 2</td></tr>
        <tr><td>Data 3</td></tr>
        <tr id="start"><td>Data 4</td></tr>
    </table>

JavaScript

function numberRows(table) {
    var rows = table.getElementsByTagName("tr");
    for (var i = 0; i < rows.length; i++) {
        rows[i].dataIndex = i;
    }
}    

numberRows(document.getElementById("tbl"));

var elem = document.getElementById("start");
alert(elem.dataIndex);