I don't think you can expire another file, I would consider any ability
to do so a bug in the browser.  Someone with too much time on their
hands could possibly turn something like that into a security risk.

I would solve the changing javascript problem by subtly altering the
pages that use the javascript file.  A web browser will recognise
menu.js, menu.js?ver=1 and menu.js?ver=2 as different pages.  You can
use this for your application by including menu.js?ver=$ver in each of
your pages.  When the menu is modified and regenerated, increment $ver.
 Every client will refetch menu.js as it views it as a different file.


David

William Lovaton wrote:
> Hello everybody,
> 
> I write here to find out if this is possible:
> 
> I want to expire an static file in the web browser through an HTTP
> header (Expires, Cache-Control or something else) sent from a PHP
> program.  The usual thing is that those headers apply only to the
> program or file sending those headers, what I want is that a program
> sends those headers to affect a different file in the browser cache.
> 
> In more detail, My web app generates a JavaScript file from the
> information stored in the database, that file represents the user menu
> and it is what the user sees in the web browser.  Now, through an apache
> directive I set expiration times for several kinds of static resources
> so the web server doesn't get slash dotted with lots of unnecessary
> requests (this is a web app with lots of traffic).
> 
> Although the JavaScript files are generated from PHP, it is seen as
> static content from the web browser POV.  Right now I have set the
> expiration time for the menu files to 20 minutes.  But let's say an
> admin user change the permissions of a user and the affected user hits a
> link that says "Regenerate menu".  What will happen is that the
> JavaScript file will be regenerated on the web server but there is a
> chance that the browser won't see the change because the file is still
> valid in the cache.
> 
> I know I could reduce the expiration time to reduce this problem but
> most of the time those files do not change.  What can I do to notify the
> web browser that the file in the cache is no longer valid?
> 
> I hope there is enough information here and that somebody can give me a
> hint in the right direction.
> 
> Thanks,
> 
> -William
> 

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