Determining a page is outdated on github pages

To have a better control of the caching of your website you can use the HTML5 cache manifest. See:

• A Beginner's Guide to Using the Application Cache on HTML5 Rocks
• Using the application cache on Mozilla Developer Network
• Cache manifest in HTML5 on Wikipedia
• Offline Web Applications W3C Working Group Note
• Offline Web applications at WHATWG

You can use the window.applicationCache.swapCache() to update the cached version of your website without the need for manually reloading the page.

This is a code example from HTML5 Rocks explaining how to update users to the newest version of your site:

// Check if a new cache is available on page load.
window.addEventListener('load', function(e) {

  window.applicationCache.addEventListener('updateready', function(e) {
    if (window.applicationCache.status == window.applicationCache.UPDATEREADY) {
      // Browser downloaded a new app cache.
      // Swap it in and reload the page to get the new hotness.
      window.applicationCache.swapCache();
      if (confirm('A new version of this site is available. Load it?')) {
        window.location.reload();
      }
    } else {
      // Manifest didn't changed. Nothing new to server.
    }
  }, false);

}, false);

To avoid some confusion I'll add that GitHub sets the correct HTTP headers for cache.manifest files:

Content-Type: text/cache-manifest
Cache-Control: max-age=0
Expires: [CURRENT TIME]

so your browser knows that it's a cache manifest and that it should always be checked for new versions.