Try it Yourself - XML dom

<!DOCTYPE html>
<html>
<body>

<p id="demo"></p>

<script>
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
   if (xhttp.readyState == 4 && xhttp.status == 200) {
   myFunction(xhttp);
   }
};
xhttp.open("GET", "books.xml", true);
xhttp.send();

function myFunction(xml) {
   var x, newComment, xmlDoc;
   xmlDoc = xml.responseXML;
   newComment = xmlDoc.createComment("Revised April 2015");
   x = xmlDoc.getElementsByTagName("book")[0];
   x.appendChild(newComment);
   document.getElementById("demo").innerHTML = x.lastChild.nodeValue;
}
</script>

</body>
</html>