A great writeup from Jake Archibald about the downfalls and downfalls to Application Cache. Having just attempted to building a mobile site using application cache, I remember hitting almost all of these gotchas and realizing that Application Cache wasn't all it made itself to seem. I resorted to actually making a mobile app rather than deal with the manifest file and it's counter-intuitive caching. This article would have helped immensely and I can't tell you how entertaining it is to read anything by Jake.
This magic button is almost always forgotten, but 90% of the time when you don’t see what you think you should be seeing on a webpage, the culprit is the same: cache.
Imagine: a few hours after discussing some edits to your site with your trusted designer. Your designer says he just updated the graphics or layout of your website and you’re excited to see it. You go to your favorite browser (which I hope is not IE), and type in your url. “Hm, that’s funny, I thought they said it was updated, do they think every day is April Fools or something?!” Then after an email and a phone call they confirm that they did update the page, you go back to it once again and still don’t see anything different! By this time you are wishing you could reach through the phone and smack somebody. You look on a different computer and see the update, and are beyond confused when you go to your computer and still don’t see the update.
Eventually, the designer tells you to try refreshing or clearing your cache. That sounds like a good plan, but what the heck is he talking about? Cache is one way smart guys have determined the internet can work better and faster. Essentially when your browser (for example Firefox, Safari or Internet Explorer) views a webpage it copies it from the internet to your computer. Then if you view that page again your browser remembers that it’s seen it recently, so it displays your local copy rather than connect with the server and download a new copy every single time. Especially with linked images and files such as style sheets and scripts. This helps you see the internet and websites faster. This is a good thing except when you want to see the most updated version in your browser.
There are however a couple ways you may tell the browser to forget the cached version of the page and load it all fresh from the server. The standard shortcuts are (windows) ‘ctrl + F5’ and (mac) ‘cmd + R’. You can also go to your browser options and delete browser history, but that will clear all your cache and not just the page you are on. This is almost always the case when you’re not seeing what you should be seeing on a site. So next time it happens, take a moment and hit F5 to save a headache.