How to get row index and cellindex together in javascript

JavaScript
<html>
<head>
    <title>Read Data from HTML Table uisng JavaScript</title>
    <style>
        th, td, p, input {
            font:14px Verdana;
        }
        table, th, td 
        {
            border: solid 1px #DDD;
            border-collapse: collapse;
            padding: 2px 3px;
            text-align: center;
        }
        th {
            font-weight:bold;
        }
    </style>
</head>

<body>
    <table id="empTable">
        <tr>    
            <th id="id">ID</th>
                <th id="emp">Employee Name</th>
                    <th id="age">Age</th>
        </tr>
        <tr><td>01</td><td>Alpha</td><td>37</td></tr>
        <tr><td>02</td><td>Bravo</td><td>29</td></tr>
        <tr><td>03</td><td>Charlie</td><td>32</td></tr>
    </table>

    <p><select name="select" id="opt">
        <option value="">--Select a Value--</option>
        <option value="id">ID</option>
        <option value="emp">Employee Name</option>
        <option value="age">Age</option></select>
    </p>

    <input type="button" id="bt" value="Show Data" onclick="showTableData()" />
    <p id="info" style="font-style:italic;"></p>
</body>

<script>    
    function showTableData() { 
        document.getElementById('info').innerHTML = ""; 
        var myTab = document.getElementById('empTable'); 
        var opt = document.getElementById("opt").value; 
        var index = document.getElementById(opt).cellIndex; 
        
        for (i = 1; i < myTab.rows.length; i++) { 
            var objCells = myTab.rows.item(i).cells; 
            
            for (var j = index; j <= index; j++) { 
                info.innerHTML = info.innerHTML + ' ' + objCells.item(j).innerHTML; 
            } 
            
            info.innerHTML = info.innerHTML + '<br />'; 
        } 
    }
</script>
</html>
Source

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