Getting Undefined Error while printing iframe through Ctrl+P

Getting Undefined Error while printing iframe through Ctrl+P

I have a document which pops up on the site within a JQuery Modal Box. The document has a print button at the end which just prints the document in the Pop-Up Box.

I wanted to print the document, only within the iframe, through Ctrl+P. That required preventing default behavior of printing all the page including the background. 
This is the JQuery Code for the printing:-

  1. $(document).keydown(function(event) {
  2.             if ( ( (event.ctrlKey == true) || (event.metaKey == true) ) && (event.which == '80')) { //Ctrl+P or Cmd + P
  3.                 event.preventDefault();
  4.                 printAssessment();
  5.             }
  6.            
  7.         });
  8.     
  9.         function printAssessment() {
  10.             if ($('#frameContainer').length) {
  11.                 $('#lightboxFrame')[0].contentWindow.print();    
  12.             }

  14.         }

The HTML for my page with the iframe is below:-

  1.     <div id="frameContainer">
  2.           <iframe id="lightboxFrame" width="950px" scrolling="auto" height="500px">
  3.              <!DOCTYPE html>
  4.                <html>
  5.                  <head>
  6.                     <body> (Whole Document in a Div) </body>
  7.                  ...

Now, the problem is that when I open up my modal box and press Ctrl+P, it prints if I don't scroll the modal, in the way I want it to be. But if I scroll the modal, and then press Ctrl+P, it gives me the following error:-

  1.     Uncaught TypeError: Cannot read property 'contentWindow' of undefined 

Strangely, even though when iframe is open, it still finds it undefined, but only when I scroll the modal iframe. If I just open the modal and press Ctrl+P, it prints fine.


Any help please?

Thanks.