15
If you can use jQuery it could be something like this
$("yourtdselector").closest("tr").attr("class","classname");
For your code
<tr>
<td onclick="changeClass(this,'classname')">My TD</td>
</tr>
function changeClass(elem, class)
{
elem.parentNode.className = class;
}
Without any extra framework:
document.getElementById("theTableName").rows[1].cells[1].className = "someclassname";