How to form this xml in javascript?

To form xml dynamically :

<script>
// Simple helper function creates a new element from a name, so you don't have to add the brackets etc.
$.createElement = function (name) {
    return $('<' + name + ' />');
};

// JQ plugin appends a new element created from 'name' to each matched element.
$.fn.appendNewElement = function (name) {
    this.each(function (i) {
        $(this).append('<' + name + ' />');
    });
    return this;
}

/* xml root element - because html() does not include the root element and we want to 
 * include <Employee /> in the output. There may be a better way to do this.
 */
var $root = $('<XMLDocument />');

$root.append
(
    // one method of adding a basic structure
    $('<Employee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>').append
    (

            $('<empNum />').text('1') //pass employee no

    )

);

// get a reference to Employee
var $Employee = $root.find('Employee');

// get a reference to itemlist

// or find itemlist from the $root like this: $root.find('Employee>itemlist');
var list = { id1: 'transactiondttm1', id2: 'transactiondttm2', id3: 'transactiondttm3', id4: 'transactiondttm4' }; // array with values
$.each(list, function (a, b) {
    // create 'Alice'
    var $newitemlist = $.createElement('itemlist');
    // add 'orderid' element using standard jQuery
    $newitemlist.append($('<orderid />').text(a));
    // add 'transactiondttm' element using our helper
    $newitemlist.append($.createElement('transactiondttm').text(b));

    // add 'Alice' to <itemlist />
    $Employee.append($newitemlist);
}            
);


// display the markup as text
alert($root.html());
document.write($root.html());
</script>

This is how you can generate xml in javascript/jquery Please try this and you will see output as

<?xml version="1.0" encoding="UTF-8"?>
<employee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<empnum>1</empnum>
<itemlist>
  <orderid>id1</orderid>
  <transactiondttm>transactiondttm1</transactiondttm>
</itemlist>
<itemlist>
  <orderid>id2</orderid>
  <transactiondttm>transactiondttm2</transactiondttm>
</itemlist>
<itemlist>
  <orderid>id3</orderid>
  <transactiondttm>transactiondttm3</transactiondttm>
</itemlist>
<itemlist>
  <orderid>id4</orderid>
  <transactiondttm>transactiondttm4</transactiondttm>
</itemlist>
</employee>

Hope this helps you, if Any queries feel free to ask questions :)

Reed this documentation about manipulating dom