XML DOM replaceChild() Method

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

function myFunction(xml) {
    var x, y, z, i, newNode, newTitle, newText, xmlDoc, txt;
    xmlDoc = xml.responseXML;
    txt = "";
    x = xmlDoc.documentElement;

    // Create a book element, title element and a text node
    newNode = xmlDoc.createElement("book");
    newTitle = xmlDoc.createElement("title");
    newText = xmlDoc.createTextNode("A Notebook");

    // Add a text node to the title node
    newTitle.appendChild(newText);

    // Add the title node to the book node
    newNode.appendChild(newTitle);

    y = xmlDoc.getElementsByTagName("book")[0];

    // Replace the first book node with the new book node
    x.replaceChild(newNode, y);

    z = xmlDoc.getElementsByTagName("title");
    // Output all titles
    for (i = 0; i < z.length; i++) {
        txt += z[i].childNodes[0].nodeValue + "<br>";
    }
    document.getElementById("demo").innerHTML = txt;
}

elementNode.replaceChild(new_node,old_node)