<!DOCTYPE html>
<html>
<head>
<script>
function insRow(id) {
var x = document.getElementById(id).insertRow(0);
var y = x.insertCell(0);
var z = x.insertCell(1);
y.innerHTML = z.innerHTML = "New";
}
</script>
</head>
<body>
<table id="myTable" style="border: 1px solid black">
<tr>
<td>Row1 cell1</td>
<td>Row1 cell2</td>
</tr>
<tr>
<td>Row2 cell1</td>
<td>Row2 cell2</td>
</tr>
<tr>
<td>Row3 cell1</td>
<td>Row3 cell2</td>
</tr>
</table>
<p>
<input type="button" onclick="insRow('myTable')" value="Insert row">
</p>
</body>
</html>