<html>
<body>
<p id="demo">Click the button to display the doctype name.</p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction()
{
var x=document.getElementById("demo");
x.innerHTML=document.doctype.name;
}
</script>
<p><strong>Note:</strong> In Internet Explorer 8 and earlier, the doctype property returns <em>null</em> for HTML and XHTML documents, and will only work for XML documents.</p>
</body>
</html>