Unable to get property 'appendChild' of undefined or null reference

I want to have a Loading Bar in a new window which has data coming from database and hence takes few while for the entire data to pop up, I have successfully managed to get the Loading Bar working in every other Browser other than IE (Chrome, Mozilla). I am testing it on IE 11 but get the following error.

Error:

SCRIPT5007: Unable to get property 'appendChild' of undefined or null reference

Code Snippet:

var brow_detls = navigator.userAgent.toLowerCase();
   //
//   if(!/.*msie.*|.*trident.*/i.test(brow_detls))
//   {
   var loading_bar_cont = newWindow.document.createElement("div");
   loading_bar_cont.id="container";
   loading_bar_cont.style.width="10%";loading_bar_cont.style.position="absolute"; loading_bar_cont.style.top="0px"; loading_bar_cont.style.right="150px";
   newWindow.document.body.appendChild(loading_bar_cont);

Kindly let me know the best approach to resolve this issue. As of now I am only able to by pass the Loading Bar working for IE which is not what I want.

Thanking You,

 Karthik R

 karthik.ramaswamy@gmail.com