JavaScript

I am trying to add theme on my web pages on button click, but i am unable to do it.
Would you please tell me how to do it?

//var videoName; the name of the video
var tPath = ... the URL to the XML
var var2 = ... the filename of an XML
  var xmlhttp = new XMLHttpRequest();
  xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      myFunction(this);
    }
  };
  xmlhttp.open("GET", tPath, true);
  xmlhttp.send();
function myFunction(xml) {
  var x, xmlDoc, videoName;
  xmlDoc = xml.responseXML;
  x = xmlDoc.getElementsByTagName("videoName")[0];
  videoName = (x.textContent);
  alert (videoName);
}
var playerURL = "http://" + getCookie("MediaServerGeneral") + "/IVP/demo.htm?XMLName=" + var2 + "&MediaFileName=" + videoName;

<?xml version="1.0" encoding="utf-8" ?>
<video>
	<videoName>videoName.mp4</videoName>
	<setting>
		<videoSize w="896" h="504"></videoSize>
	</setting>
</video>

In a web form 2010 application, I am creating letters that need to be sent to various customers that are generated in html and are sent to 2 or 3 customers at the at different addresses. However each letter needs to be the same. The only difference is the mailing address. Thus I need each letter to be generated on separate pages. Thus I would like to know what html command can be used to made certain each letter is printed on separate pages. Thus can you tell me what the command would be?

function js_add2Cart(_sku) {

    var $itemQty = $("#selectQty"),
        $itemType = $("#Type"),
        $spinner = $("#js-add2Cart > i"),
        $NavCart = $("#navCartCount"),
        _qty = parseInt($itemQty.val()),
        _type = $itemType.val();

    // Delay and queue the spinner for visual success<br />
    if (isNaN(_qty)) { _qty = 1; }
    $.ajax({
        type: "POST",
        cache: false,
        dataType: "json",
        url: '/Ajax/json_add2cart',
        data: { Sku: _sku, Qty: _qty, Type: _type },
        beforeSend: function () {
            $spinner.addClass('fa-cog fa-spin');
            $("#js-add2Cart").html('Add to Cart').removeClass('error').addClass('add2cart');
        },
        error: function (xhr, ajaxOptions, thrownError) {
            $("#js-add2Cart").removeClass('add2cart').addClass('error').html('Error has occured');
        },
        success: function (data) {
            // Update the Cart Qty in Store Layout<br />
            $NavCart.text(data);
        },
        complete: function () {
            $("#js-add2Cart").html('Item added');
            $spinner.removeClass('fa-cog fa-spin');
        }
    });

}