Create XML in Javascript

Disclaimer: The following answer assumes that you are using the JavaScript environment of a web browser.

JavaScript handles XML with 'XML DOM objects'. You can obtain such an object in three ways:

1. Creating a new XML DOM object

var xmlDoc = document.implementation.createDocument(null, "books");

The first argument can contain the namespace URI of the document to be created, if the document belongs to one.

Source: https://developer.mozilla.org/en-US/docs/Web/API/DOMImplementation/createDocument

2. Fetching an XML file with XMLHttpRequest

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (xhttp.readyState == 4 && xhttp.status == 200) {

    var xmlDoc = xhttp.responseXML; //important to use responseXML here
}
xhttp.open("GET", "books.xml", true);
xhttp.send();

3. Parsing a string containing serialized XML

var xmlString = "<root></root>";
var parser = new DOMParser();
var xmlDoc = parser.parseFromString(xmlString, "text/xml"); //important to use "text/xml"

When you have obtained an XML DOM object, you can use methods to manipulate it like

var node = xmlDoc.createElement("heyHo");
var elements = xmlDoc.getElementsByTagName("root");
elements[0].appendChild(node);

For a full reference, see http://www.w3schools.com/xml/dom_intro.asp

Note: It is important, that you don't use the methods provided by the document namespace, i. e.

var node = document.createElement("Item");

This will create HTML nodes instead of XML nodes and will result in a node with lower-case tag names. XML tag names are case-sensitive in contrast to HTML tag names.

You can serialize XML DOM objects like this:

var serializer = new XMLSerializer();
var xmlString = serializer.serializeToString(xmlDoc);

Consider that we need to create the following XML document:

<?xml version="1.0"?>
<people>
  <person first-name="eric" middle-initial="H" last-name="jung">
    <address street="321 south st" city="denver" state="co" country="usa"/>
    <address street="123 main st" city="arlington" state="ma" country="usa"/>
  </person>

  <person first-name="jed" last-name="brown">
    <address street="321 north st" city="atlanta" state="ga" country="usa"/>
    <address street="123 west st" city="seattle" state="wa" country="usa"/>
    <address street="321 south avenue" city="denver" state="co" country="usa"/>
  </person>
</people>

we can write the following code to generate the above XML

var doc = document.implementation.createDocument("", "", null);
var peopleElem = doc.createElement("people");

var personElem1 = doc.createElement("person");
personElem1.setAttribute("first-name", "eric");
personElem1.setAttribute("middle-initial", "h");
personElem1.setAttribute("last-name", "jung");

var addressElem1 = doc.createElement("address");
addressElem1.setAttribute("street", "321 south st");
addressElem1.setAttribute("city", "denver");
addressElem1.setAttribute("state", "co");
addressElem1.setAttribute("country", "usa");
personElem1.appendChild(addressElem1);

var addressElem2 = doc.createElement("address");
addressElem2.setAttribute("street", "123 main st");
addressElem2.setAttribute("city", "arlington");
addressElem2.setAttribute("state", "ma");
addressElem2.setAttribute("country", "usa");
personElem1.appendChild(addressElem2);

var personElem2 = doc.createElement("person");
personElem2.setAttribute("first-name", "jed");
personElem2.setAttribute("last-name", "brown");

var addressElem3 = doc.createElement("address");
addressElem3.setAttribute("street", "321 north st");
addressElem3.setAttribute("city", "atlanta");
addressElem3.setAttribute("state", "ga");
addressElem3.setAttribute("country", "usa");
personElem2.appendChild(addressElem3);

var addressElem4 = doc.createElement("address");
addressElem4.setAttribute("street", "123 west st");
addressElem4.setAttribute("city", "seattle");
addressElem4.setAttribute("state", "wa");
addressElem4.setAttribute("country", "usa");
personElem2.appendChild(addressElem4);

var addressElem5 = doc.createElement("address");
addressElem5.setAttribute("street", "321 south avenue");
addressElem5.setAttribute("city", "denver");
addressElem5.setAttribute("state", "co");
addressElem5.setAttribute("country", "usa");
personElem2.appendChild(addressElem5);

peopleElem.appendChild(personElem1);
peopleElem.appendChild(personElem2);
doc.appendChild(peopleElem);

If any text need to be written between a tag we can use innerHTML property to achieve it.

Example

elem = doc.createElement("Gender")
elem.innerHTML = "Male"
parent_elem.appendChild(elem)

For more details please follow the below link. The above example has been explained there in more details.

https://developer.mozilla.org/en-US/docs/Web/API/Document_object_model/How_to_create_a_DOM_tree