<!DOCTYPE html>
<html>
<head>
<style>
table, td {
    border: 1px solid black;
}

</style>
</head>
<body>

<p>Click the button to return the text inside the caption element.</p>

<table id="myTable">
<caption>This is a table caption</caption>
  <tr>
    <td>cell 1</td>
    <td>cell 2</td>
  </tr>
  <tr>
    <td>cell 3</td>
    <td>cell 4</td>
  </tr>
</table><br>

<button onclick="myFunction()">Try it</button>

<script>
function myFunction() {
    alert(document.getElementById("myTable").caption.innerHTML);
}
</script>

</body>
</html>