website update cache - php

Question

If you have a live website (using PHP,MySQL,JS,CSS) and say you change some functionality. What is the best way to make sure, that when a user visits the site, the changed pages are updated and not loaded from cache?

Answer 1

For that reson there is file loaders made for. When you load css, js or any other file, you must set cache control header. You can do it by editing .htaccess or with php.
.htaccess demo
<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault A300
ExpiresByType image/x-icon A2592000
ExpiresByType application/x-javascript A3600
ExpiresByType text/css A3600
ExpiresByType image/gif A604800
ExpiresByType image/png A604800
ExpiresByType image/jpeg A604800
ExpiresByType text/plain A300
ExpiresByType application/x-shockwave-flash A604800
ExpiresByType video/x-flv A604800
ExpiresByType application/pdf A604800
ExpiresByType text/html A300
</IfModule>
PHP demo:
$offset = 3600 * 24;
$expire = "Expires: " . gmdate("D, d M Y H:i:s", time() + $offset) . " GMT";
header($expire);

Answer 2

Via HTML, in the Head section put...
<META HTTP-EQUIV="CACHE-CONTROL" CONTENT="NO-CACHE">
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Expires" CONTENT="-1">

Answer 3

You can't really control the policy each browser, if it complies to the standards, but what commonly happens is the browser does download the header from each HTML before deciding whether or not it should be loaded from cache or re-downloaded.
Check RFC HTTP 1.1 Header Field for more details (under cache control in particular)

Answer 4

Unless you have some form of caching the user will be requesting data and checking if it has been updated. Usually your PHP is not cached unless you have active caching.
Your JS and CSS would have to be set via HEADERS under say Apache (or whatever web server you utilize).

Answer 5

You can use the window.applicationCache.swapCache(); and window.location.reload(); to force reload the page once javascript confirms that there's an updated version of the site.
A better option may be to prompt the user in some way, letting them know that the site updated. That way, the page doesn't just suddenly reload.
function updateCache(){
window.applicationCache.swapCache();
window.location.reload();
}
window.applicationCache.addEventListener("updateready", updateCache, false);