Is My Page Being Loaded from the Browser Cache?

Question

I have a "new items" badge on a page that I want to update immediately the page is loaded from the cache (i.e. when hitting "Back" or "Forward" to return to this page). What is the best way to accomplish this?

The setup is pretty simple. The layout for the app looks for new items every 8 seconds, and updates the badge + list of items accordingly.

$(function() {
    setInterval( App.pollForNewItems, 8000 );
});

When someone navigates away from this page to look at the details of an item, a lot can happen. Things are "new" until any user has viewed them, and the app will likely have several user using it simultaneously (the kind of workflow used for a call center or support tickets).

To make sure that the badges are always up to date, I have:

$(window).bind('focus load', function ( event ) {
    App.pollForNewItems();
});

..And though this works, polling for new items on 'load' is only useful when the page is loaded from the cache. Is there a reliable cross-browser way to tell if a page is being loaded from the cache?

Answer 1

Navigation Timing is in most browsers now(ie9+) http://www.w3.org/TR/navigation-timing/#sec-navigation-info-interface

 if (!!window.performance && window.performance.navigation.type === 2) {
   // page has been hit using back or forward buttons
 } else {
   // regular page hit
 }

Answer 2

You can ask the web browser to not cache the page. Try these HTTP headers:

Cache-control: no-cache
Cache-control: no-store
Pragma: no-cache
Expires: 0

Particularly, Cache-control: no-store is interesting because it tells the browser to not store the page in memory at all which prevents a stale page being loaded when you hit the back/forward button.

If you do this instead, you don't have to poll for data on page load.