Matthew Haines-Young

Minification & concatenation of JS and CSS files can reduce the file size of your assets, and reduce the number of HTTP requests, helping improve page load times.
The plugin takes a manually defined list of script/style handles, and minifies and concatenates them into a single file which is then cached for future use.
Features.
<ul>
<li>Minifies & concatenates scripts and styles loaded using the WordPress dependency enqueueing system.</li>
<li>Handles scripts loaded in the header & footer.</li>
<li>Complete control – only a manually defined list of files is processed.</li>
<li>Multiple, independently processed files.</li>
<li>Minified files are only loaded if at least one component file should be loaded.</li>
<li>Compatable with localized scripts.</li>
<li>Helper tool – displays a list of scripts and styles enqueued on each page on the front end of the site.</li>
</ul>

MinQueue

Minify & Concatenate Enqueued Scripts & Styles.

Weston Ruter

Nashwan D

Frankie Jarrett

Shadi Sharaf

Dzikri Aziz

Chris Olbekson

lkraav

This plugin takes all scripts and stylesheets that have been added via <code>wp_enqueue_script</code> and <code>wp_enqueue_style</code> 
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. <code>print</code>) 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 <a href="https://wordpress.org/plugins/optimize-scripts/" rel="ugc">Optimize Scripts</a> plugin, 
which this plugin now supersedes.
Features:
<ul>
<li>Minified sources are stored in the WP Options table so no special filesystem access is required.</li>
<li>Endpoint for minified requests is at <code>/_minified</code>, which can be configured.</li>
<li>Admin page for taking inventory of minified scripts and stylesheets, with methods for expiring or purging the cached data.</li>
<li>Dependencies which must not be minified may be excluded via the <code>dependency_minification_excluded</code> filter.</li>
<li>Dependencies hosted on other domains are by default excluded, but this behavior can be changed by filtering the <code>default_exclude_remote_dependencies</code> option via the <code>dependency_minification_options</code> filter, or on a case-by-case basis via the filter previously mentioned.</li>
<li>By default excludes external scripts from being concatenated and minified, but they can be opted in via the <code>dependency_minification_excluded</code> filter.</li>
<li>The length of time that a minified source is cached defaults to 1 month, but can be configured via the <code>cache_control_max_age_cache</code> option.</li>
<li>If a minified source is not available yet, the page source will note that the dependency minification process is pending.</li>
<li>Any errors that occur during minification will be shown on the frontend in comments if the <code>show_error_messages</code> option is enabled; such errors are enabled by default if <code>WP_DEBUG</code>.</li>
<li>If the minification process errors out, the original unminified sources are served and the error is cached for 1 hour (by default, configured via <code>cache_control_max_age_error</code>) to prevent back-to-back crons from continually attempting to minify in perpetuity.</li>
<li>Cached minified sources are served with <code>Last-Modified</code> and <code>ETag</code> responses headers and requests will honor <code>If-None-Match</code> and <code>If-Modified-Since</code> to return <code>304 Not Modified</code> responses (configurable via the <code>allow_not_modified_responses</code> option).</li>
<li>Data attached to scripts (e.g. via <code>wp_localize_script</code>) is also concatenated together and attached to the newly-minified script.</li>
<li>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.</li>
<li>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.</li>
<li>Can serve compressed responses with <code>gzip</code> or <code>deflate</code>.</li>
<li>Transforms relatives paths in stylesheets (e.g. background-images) to absolute ones, so that they don’t 404.</li>
</ul>
Development of this plugin is done <a href="https://github.com/x-team/wp-dependency-minification" rel="nofollow ugc">on GitHub</a>. Pull requests welcome. Please see <a href="https://github.com/x-team/wp-dependency-minification/issues" rel="nofollow ugc">issues</a> 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 <code>css|js</code> from this rule in <code>nginx-wp-common.conf</code> (or remove the rule altogether):
<pre><code># 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;
}
</code></pre>

Dependency Minification

Automatically concatenates and minifies any scripts and stylesheets enqueued using the standard dependency system.

MinQueue vs Dependency Minification