Q:

document.write Not working when loading external Javascript source

I'm trying to load an external JavaScript file dynamically into an HTML element to preview an ad tag. The script loads and executes but the script contains "document.write" which has an issue executing properly but there are no errors. 
<html>
    <head>
        <script src="//ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
        <script type="text/javascript">
        $(function() {
            source = 'http://ib.adnxs.com/ttj?id=555281';

            // DOM Insert Approach
            // -----------------------------------
            var script = document.createElement('script');
                script.setAttribute('type', 'text/javascript');
                script.setAttribute('src', source);

            document.body.appendChild(script);
        });
        </script>
    </head>

<body>
</body>
</html>

I can get it to work if

If i move the the source to the same domain for testing
If the script was modified to use document.createElement and appendChild instead of document.write like the code above. 

I don't have the ability to modify the script since it being generated and hosted by a 3rd party.
Does anyone know why the document.write will not work correctly? And is there a way to get around this?
Thanks for the help!

A:

Another solution is to create an iframe, then load the script inside that iframe when the ajax call is ready:
var iframe = document.createElement('iframe');
document.body.appendChild(iframe);
var doc = iframe.contentWindow.document;

// do this whenever you want (f.ex after ajax is made):
doc.open();
doc.write('<script src="http://ib.adnxs.com/ttj?id=555281">\x3C/script>');
doc.close();

That way, the document.write in the end script will not affect your site, just the iframe. You will need to style the iframe to fit the ad.

