We\'re facing a fairly scary issue in JavaScript that none of us seems to be quite capable of resolving:
How do we get the width and height of a DOM element, including
The problem here is you can't get the element size before you add this element on the page.
On your method "constructElement", you adding the element to a root element, but just on onload you adding to the page. Your property "rootElement" not have the size properties setted.
Rethink the structure of your object/method if you want to manipulate these properties.
Look my update of your fiddle
$(function ()
{
var ex = new exampleElement("Hello", "Here's text");
ex.constructElement();
document.body.appendChild(ex.rootElement);
$("")
.text(" => Width is " + $("div").width() + ", and Height is " + $("div").height())
.appendTo($("div p"));
});