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<!DOCTYPE html>
<html>
<head>
<style>
table, th, td {
  border: 1px solid black;
}
</style>
</head>
<body>
<p>Click the button to return the value of the colspan attribute of th with id "myTh".</p>
<table>
  <tr>
    <th id="myTh" colspan="2">Month</th>
    <th>Savings</th>
  </tr>
  <tr>
    <td>January</td>
    <td>$100</td>
  </tr>
  <tr>
    <td>February</td>
    <td>$100</td>
  </tr>
</table>
<br> 
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction(x) {
  var x = document.getElementById("myTh").colSpan;
  document.getElementById("demo").innerHTML = "The value of colspan is: " + x;
}
</script>
</body>
</html>