What requests do browsers' "F5" and "Ctrl + F5" refreshes generate?

Posted by Morgan Cheng on Stack Overflow See other posts from Stack Overflow or by Morgan Cheng
Published on 2008-12-22T02:00:08Z Indexed on 2011/01/06 20:54 UTC
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browser

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caching

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cross-browser

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refresh

Is there a standard for what actions F5 and Ctrl+F5 trigger in web browsers?

I once did experiment in IE6 and Firefox 2.x. The "F5" refresh would trigger a HTTP request sent to the server with an "If-Modified-Since" header, while "Ctrl+F5" would not have such a header. In my understanding, F5 will try to utilize cached content as much as possible, while "Ctrl+F5" is intended to abandon all cached content and just retrieve all content from the servers again.

But today, I noticed that in some of the latest browsers (Chrome, IE8) it doesn't work in this way anymore. Both "F5" and "Ctrl+F5" send the "If-Modified-Since" header.

So how is this supposed to work, or (if there is no standard) how do the major browsers differ in how they implement these refresh features?

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