<table>
    <th id="h1">Header 1</td>
    <td id="c1">Cell 1</td>
    <script></script>
    <td id="c2">Cell 2</td>
</table>

<script>
function outputIndex(name) {
    node = document.getElementById(name);
    document.writeln(name + " has index " + node.cellIndex + "<br>");
}

outputIndex("h1");
outputIndex("c1");
outputIndex("c2");
</script>