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JavaScript Minification in DXP

This article describes DXP infrastructure to minify JavaScript source files. It is related to Resource Serving in DXP.

MinifierUtil, JavaScriptMinifier and frontend-js-minifier

These three pieces form the basic infrastructure available in DXP to minify JavaScript code.

  • JavaScriptMinifier: describes the interface that services to minify JavaScript must implement.

  • MinifierUtil: provides a way to retrieve the JavaScriptMinifier with highest service ranking currently deployed to DXP. Note that you can also obtain a reference to a JavaScriptMinifier (or all of them) using standard OSGi mechanisms (for example: @Component or ServiceTracker).

  • frontend-js-minifier: this project contains the two default minifiers that DXP ships out-of-the-box (Google and Yahoo). See the two following sections for more details.

Note that, even though, JavaScriptMinifier and MinifierUtil are inside portal-impl to maintain backward compatibility, the implementation of the minifiers has been extracted to an OSGi module (frontend-js-minifier) for modularity.

GoogleJavaScriptMinifier

This is the default DXP minifier (because it is deployed with a higher service ranking than the other ones available).

It uses Google Closure Compiler under the hood. Because this is an internal library from Google (thus unsupported and subject to big breaking changes) updating it usually has a significant cost so it is not done very often.

YahooJavaScriptMinifier

This uses YUI Compressor from Yahoo!, which is still active but unmaintained (except for some PRs that get merged from time to time). The last commit at the time of this writing (Sep 2020) is from May 2019.

Unless someone has a very good reason to use it, this shouldn't be the choice for any production site but it is still shipped for compatibility reasons.

Components of DXP using the minifier

Currently, the following components in DXP use the minifier services.

StripFilter

This is a filter used to minify inline JavaScript code contained in <script> tags and embedded in the HTML code.

It also does transformations for <input>, <textarea>, <pre> and <style> but that's out of the scope of this document.

It filters any resource with its URL starting with (as specified in liferay-web.xml):

  • /c/...
  • /group/...
  • /user/...
  • /web/...

And it can be configured with:

  • portal.properties:
    • minifier.inline.content.cache.enabled: set to true to make the filter minify <script> tags content (by default, true).
    • minifier.inline.content.cache.skip.javascript: this defines a comma separated list of tokens to look for in the <script> content so that, if any is found, the minified response is not cached. By default, any <script> containing getSessionId or encryptedUserId is not cached.
    • strip.ignore.paths: list of paths to ignore (by default, /document_library/get_file).
    • strip.mime.types in portal.properties: defines the MIME types of responses that should be processed by the filter (by default, text/html* and text/xml*). Note that you can put a * at the end of the config values to catch all MIME types starting with the string to the left of the *.
  • Request parameters:

If all the rules match and a <script> is minified, the filter simply invokes MinifierUtil.minifyJavaScript() to do its duty.

AggregateFilter

This filter is already described in Resource Serving in DXP.

ComboServlet

This servlet aggregates several .js or .css files and serves them as a single request to ease caching and reduce connection count. It also caches its responses.

It honors the work.dir.override.enabled portal property so if it is set to true it diverts requests to development project folders when using fast deployments.

The way to invalidate this servlet's cache is to check if any of the aggregated files has changed. If the portal property combo.check.timestamp is set to false (and by default, it is, in production systems) the check is not performed and the cache is never invalidated. Otherwise files are tested for changes every combo.check.timestamp.interval milliseconds (where combo.check.timestamp.interval is a configuration value of portal.properties).

Finally, each .js file aggregated by the servlet has its name tested for the -min.js or .min.js suffixes and, if they are NOT found, its content is minified using MinifierUtil.minifyJavaScript().

JSLoaderConfigServlet

This servlet services request to the /js_loader_config URL, which returns the AMD Loader configuration so that the browser side can access it.

For example, it sets the following loader properties: explainResolutions, logLevel, resolvePath and waitTimeout.

It also controls the value of Liferay.EXPLOSE_GLOBAL which causes Liferay.Loader.define() method to be published under window.define (this is for compatiblity reasons, but its use is strongly discouraged as it can cause issues with third party libraries).

Even though it is small, this servlet minifies its response with MinifierUtil.minifyJavaScript() and also caches it for efficiency.

JSBundleConfigServlet

This servlet services request to the /js_bundle_config URL, which is the configurator of the legacy AUI loader.

This servlet does not cache its response but minifies it leveraging MinifierUtil.minifyJavaScript().