<html>
<head>
<script type="text/javascript">
function changeWidth()
{
document.getElementById("td1").width="200px";
}
</script>
</head>
<body>
<table border="1">
<tr>
<th>Firstname</th>
<th>Lastname</th>
</tr>
<td id="td1">Peter</td>
<td id="td2">Griffin</td>
</table>
<br />
<input type="button" onclick=changeWidth() value="Change width" />
</body>
</html>