JavaScript控制表格单元格垂直对齐

<!DOCTYPE html>
<html>
<head>
<script>
function valignCell()
{
var x=document.getElementById('myTable').rows[0].cells;
x[0].vAlign="bottom";
}
</script>
</head>
<body>
<table id="myTable" border="1" height="70%">
<tr>
<td>First cell</td>
<td>Second cell</td>
</tr>
<tr>
<td>Third cell</td>
<td>Fourth cell</td>
</tr>
</table>
<form>
<input type="button" onclick="valignCell()"
value="Vertical align cell content">
</form>
</body>
</html>