Dependency Minification

This plugin takes all scripts and stylesheets that have been added via wp_enqueue_script and wp_enqueue_style
and automatically concatenates and minifies them into logical groups. For example, scripts in the footer get grouped
together and styles with the same media (e.g. print) get minified together. Minification is done via WP-Cron in order
to prevent race conditions and to ensure that the minification process does not slow down page responses.

This is a reincarnation and rewrite of the Optimize Scripts plugin,
which this plugin now supersedes.

Features:

• Minified sources are stored in the WP Options table so no special filesystem access is required.
• Endpoint for minified requests is at /_minified, which can be configured.
• Admin page for taking inventory of minified scripts and stylesheets, with methods for expiring or purging the cached data.
• Dependencies which must not be minified may be excluded via the dependency_minification_excluded filter.
• Dependencies hosted on other domains are by default excluded, but this behavior can be changed by filtering the default_exclude_remote_dependencies option via the dependency_minification_options filter, or on a case-by-case basis via the filter previously mentioned.
• By default excludes external scripts from being concatenated and minified, but they can be opted in via the dependency_minification_excluded filter.
• The length of time that a minified source is cached defaults to 1 month, but can be configured via the cache_control_max_age_cache option.
• If a minified source is not available yet, the page source will note that the dependency minification process is pending.
• Any errors that occur during minification will be shown on the frontend in comments if the show_error_messages option is enabled; such errors are enabled by default if WP_DEBUG.
• If the minification process errors out, the original unminified sources are served and the error is cached for 1 hour (by default, configured via cache_control_max_age_error) to prevent back-to-back crons from continually attempting to minify in perpetuity.
• Cached minified sources are served with Last-Modified and ETag responses headers and requests will honor If-None-Match and If-Modified-Since to return 304 Not Modified responses (configurable via the allow_not_modified_responses option).
• Data attached to scripts (e.g. via wp_localize_script) is also concatenated together and attached to the newly-minified script.
• WP-Cron is utilized to initiate the minification process in order to prevent race conditions, and to ensure that page responses aren’t slowed down.
• Stale minified scripts and stylesheets remain until replaced by refreshed ones; this ensures that full-page caches which reference stale minified sources won’t result in any 404s.
• Can serve compressed responses with gzip or deflate.
• Transforms relatives paths in stylesheets (e.g. background-images) to absolute ones, so that they don’t 404.

Development of this plugin is done on GitHub. Pull requests welcome. Please see issues reported there before going to the plugin forum.

If you are using Nginx with the default Varying Vagrant Vagrants config, you’ll want to remove css|js from this rule in nginx-wp-common.conf (or remove the rule altogether):

# Handle all static assets by serving the file directly. Add directives 
# to send expires headers and turn off 404 error logging.
location ~* \.(js|css|png|jpg|jpeg|gif|ico)$ {
    expires 24h;
    log_not_found off;
}