Admin Forum:Why does preview page take off all java effects?

We all know that page preview is slightly different from what we have on real page. First of all, it takes off every javascript effect, and it has different width than real page (preview is smaller), so the page layout is not exactly the same. I started asking myself "why". Is there a reason for this mismatch?
 * The preview is the same width as a page with the rail showing, give or take a few pixels. I don't know for sure, but it's probably because javascript is either executed on page load or when you trigger another event eg. clicking a button, hovering over something. If the preview loaded on a completely new page, it would probably be affected by javascript, but it doesn't. When you preview a page, the text in the edit box is passed to the server and the response is injected dynamically into the page -- it doesn't actually load a new page. Javascript doesn't just listen for changes to the page. It isn't that flexible. — Matthew2602 (talk) 11:25, June 22, 2012 (UTC)
 * I think Wikia could keep their previous function: reloading the page completely instead of adding a new layer (this is the way Wikipedia is still using) which allows me to see how my coding works by just a simple click on preview. I'm pretty liking Wikia's own preview function, but saving my edit every time and polluting page history to verify js work is not that funny.
 * Well, one upside is that you don't have to load the page again every time, so you don't have to go through all the HTTP requests again. That would be particularly useful on slower connections, especially if you were proofing something and were previewing it multiple times. You could always create a sandbox in your userspace on the wiki, or if your code isn't specific-wiki dependent, you could even create a completely separate test wiki. It might sound a bit elaborate, but it can be a good idea when you're making forward of tens to hundreds of revisions to a piece of code. — Matthew2602 (talk) 12:18, June 22, 2012 (UTC)