<!DOCTYPE html>
<html>
<head>
<style>
table, th, td {
border: 1px solid black;
}
</style>
</head>
<body>
<h3>A demonstration of how to access a COLGROUP element</h3>
<table>
<colgroup id="myColgroup" span="2" style="background:red"></colgroup>
<tr>
<th>ISBN</th>
<th>Title</th>
<th>Price</th>
</tr>
<tr>
<td>3476896</td>
<td>My first HTML</td>
<td>$53</td>
</tr>
<tr>
<td>5869207</td>
<td>My first CSS</td>
<td>$49</td>
</tr>
</table>
<p>Click the button to get the number of columns a COLGROUP element should span.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var x = document.getElementById("myColgroup").span;
document.getElementById("demo").innerHTML = x;
}
</script>
</body>
</html>