​x
 
<html>
<head>
<script type="text/javascript">
function insCell()
  {
  var x=document.getElementById('tr2').insertCell(0)
  x.innerHTML="John"
  }
</script>
</head>
<body>
​
<table border="1">
<tr id="tr1">
<th>Firstname</th>
<th>Lastname</th>
</tr>
<tr id="tr2">
<td>Peter</td>
<td>Griffin</td>
</tr>
</table>
<br />
<input type="button" onclick="insCell()" value="插入单元">
​
</body>
</html>
​