Hiding Iframe horizontal scroll via javascript?

I have a javascript program that creates an iframe lightbox. This is the section of the code that affects the iframe only.

mediaType = 'url';
            mediaWidth = mediaWidth || "640px";
            mediaHeight = mediaHeight || "360px";
            mediaId = "mediaId_"+new Date().getTime();  
            preload = new Element('iframe', {
                'src': URL,
                 'id': mediaId,
                 width: mediaWidth,
                 height: mediaHeight,
                 'frameborder': 0

I have no idea how to make the iframe not have an x scroll in this particular code. The css for the Js app only applies to the background, so I don't think I can alter it there.

Is there nothing in js that can achieve hiding a scroll, or is this program's line of code too hard to understand for most people (works in a specific way that only those associated with program would know)?

[Troy III]

you sohuld make the content fit the iFrame or
use CSS overflow: hidden;
or

overflow-x: hidden