Chrome refuses to cache Javascript

Question

I am reasonably new to browser caching. I am attempting to get Chrome to permanently cache any static file with a query parameter (for cache busting purposes). I have set Cache-Control and Expires headers way into the future, which should be adequate to say "cache this forever". The resulting response headers:

HTTP/1.1 200 OK
Cache-Control: public, max-age=315360000
Connection: keep-alive
Content-Encoding: gzip
Content-Type: application/x-javascript
Date: Wed, 16 Jul 2014 09:29:54 GMT
Last-Modified: Wed, 16 Jul 2014 03:44:14 GMT
Server: nginx/1.6.0
Transfer-Encoding: chunked
Vary: Accept-Encoding

Firefox and Safari seem to respect this for all cachebusted (?v= query parameter) files. Chrome mostly follows the directives, except for Javascript. Most of the time it does a request with an If-Modified-Since header rather than loading from cache. Sometimes one of them will load from cache and the other will yield a request resulting in a 304. Usually when loading the page from a new tab it will load from cache, but not if you hit enter in the address bar.

I've observed other websites using what I think are the exact same headers, and the files are always loaded from cache. Some of them load from cache even if you do a refresh.

I understand cache behaviour is somewhat unpredictable, but I want to make sure I'm not overseeing something that's making Chrome do that?

Answer 1

I had the same issue with chrome and after some hours of trial and error I figuered out, that chrome seems to have a problem with the Vary Header

I've got this snippet in my Apache / .htaccess config and as soon as I comment the line "Header append Vary Accept-Encoding" Chrome starts caching .js and .css files

  <FilesMatch "(\.js\.gz|\.css\.gz)$">
  # Serve correct encoding type.
  Header set Content-Encoding gzip
  # Force proxies to cache gzipped & non-gzipped css/js files separately.
  #Header append Vary Accept-Encoding
</FilesMatch>

It still does not work while running the request via our nignx server, because it is adding the Vary: Accept-Encoding header too, when delivering gzip compressed.

So far I can guess this is a problem that only happens with chrome and as a workaround I would change the configuration to append the header only if chrome (haven't checked for safari) is not the client until there is a better fix:

<FilesMatch "(\.js\.gz|\.css\.gz)$">
  # Serve correct encoding type.
  Header set Content-Encoding gzip
  # Force proxies to cache gzipped & non-gzipped css/js files separately.
  BrowserMatch "Chrome" ChromeFound
  Header append Vary Accept-Encoding env=!ChromeFound
</FilesMatch>