<!DOCTYPE html>
<html>
<head>
<script>
function changeBorder(id) {
document.getElementById(id).style.border = "5px solid";
}
</script>
</head>
<body>
<table style="border:1px solid black" id="myTable">
<tr>
<td>100</td>
<td>200</td>
</tr>
<tr>
<td>300</td>
<td>400</td>
</tr>
</table>
<p>
<input type="button" onclick="changeBorder('myTable')" value="Change Border">
</p>
</body>
</html>