With a single page app, where I change the hash and load and change only the content of the page, I'm trying to decide on how to manage the JavaScript that each "page" might need.

I've already got a History module monitoring the location hash which could look like domain.com/#/company/about, and a Page class that will use XHR to get the content and insert it into the content area.

function onHashChange(hash) {
    var skipCache = false;
    if(hash in noCacheList) {
        skipCache = true;
    } 
    new Page(hash, skipCache).insert();
}


// Page.js
var _pageCache = {};
function Page(url, skipCache) {

    if(!skipCache && (url in _pageCache)) {
        return _pageCache[url];
    }
    this.url = url;
    this.load();

}

The cache should let pages that have already been loaded skip the XHR. I also am storing the content into a documentFragment, and then pulling the current content out of the document when I insert the new Page, so I the browser will only have to build the DOM for the fragment once.

Skipping the cache could be desired if the page has time sensitive data.

Here's what I need help deciding on: It's very likely that any of the pages that get loaded will have some of their own JavaScript to control the page. Like if the page will use Tabs, needs a slide show, has some sort of animation, has an ajax form, or what-have-you.

What exactly is the best way to go around loading that JavaScript into the page? Include the script tags in the documentFragment I get back from the XHR? What if I need to skip the cache, and re-download the fragment. I feel the exact same JavaScript being called a second time might cause conflicts, like redeclaring the same variables.

Would the better way be to attach the scripts to the head when grabbing the new Page? That would require the original page know all the assets that every other page might need.

And besides knowing the best way to include everything, won't I need to worry about memory management, and possible leaks of loading so many different JavaScript bits into a single page instance?