title: Detecting if a browser's cache is full
body: <p>We've identified that full browser caches are the cause of a problem on our extranet. It only affects a small number of our users, but we'd like to alert them to the problem and give them some guidance on how to fix the problem for themselves.</p>
  
  <p>We'd like to use a similar system to the one which GMail uses. When it detects that your browser's cache <strike>is full</strike> is not behaving as it should, it shows a warning message telling users that their cache is full and that it may cause problems with GMail, along with a link to a <a href="http://mail.google.com/support/bin/answer.py?answer=8840#" rel="nofollow noreferrer">Gmail Help page on clearing your browser's cache</a>.</p>
  
  <p>Does anyone know if there any resources out there, or examples of how to use JavaScript to detect that the browser's cache is <strike>full</strike> behaving badly?</p>
  
  <p>Thanks.</p>
  
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  <p><strong>Clarification:</strong> What we're actually trying to detect, I suppose, is not whether or not the cache is full, but rather whether a script, which we have configured server-side to be stored in the cache, is being re-requested from the server - in such a way that the browser is behaving strangely, or as if its cache is not behaving as it should.</p>
  
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  <p><strong>Further Clarification:</strong> Thank you all for the updates on caching. Our scripts are being sent with the correct headers, and we're only seeing this problem in IE6 and IE7 - Mozilla and WebKit browsers seem to be unaffected - but I'm still not sure on how exactly we'd go about using JavaScript and/or XmlHttpRequest to check to see whether or not an object was retrieved from the cache, thus letting us check whether the cache is behaving badly.</p>