​x
 
<html>
<head>
<script type="text/javascript">
function leftAlign()
  {
  document.getElementById('header').align="left";
  }
</script>
</head>
<body>
​
<table width="100%" border="1">
<tr id="header">
<th>名</th>
<th>姓</th>
</tr>
<tr>
<td>John</td>
<td>Adams</td>
</tr>
</table>
<br />
<input type="button" onclick="leftAlign()" value="左对齐表格行" />
​
</body>
</html>
​