Change the minification engine for client libraries in AEM

AEM 6.2, 6.3 and later versions

In AEM6.2 and later versions, you can set properties on cq:ClientLibraryFolder nodes that let you swap out yui engine with GCC (Google Clojure Compiler https://github.com/google/closure-compiler-js). 

For example, see these client library nodes that use GCC for js:
/libs/granite/contexthub/dependencies/coralui
/etc/clientlibs/granite/coralui3
/etc/clientlibs/granite/coralui2
/libs/dam/gui/coral/components/admin/adhocassetshare/clientlibs/adhocassetshare
/libs/dam/gui/components/admin/adhocassetshare/clientlibs/shareembedded
/etc/clientlibs/screens/player/shared
/etc/clientlibs/screens/player/firmware
/libs/dam/gui/components/admin/adhocassetshare/clientlibs/shareembeddedpreview
/apps/geometrixx-instore/clientlibs

In addition, if you want to implement your own custom script processor, then you would implement this java interface:
com.adobe.granite.ui.clientlibs.script.ScriptProcessor

https://docs.adobe.com/docs/en/aem/6-2/develop/ref/diff-previous/changes/pkg_com.adobe.granite.ui.clientlibs.script.html

This allows you to define ScriptProcessors that can modify script sources:

• the processors are configurable with options
• the processor can be used for minification, but also for non-minified cases
• a property on the cq:ClientLibraryFolder node allows you to define which processor to use

• These extra multivalue properties can be set on the cq:ClientLibraryFolder node: cssProcessor and jsProcessor.
• The default ScriptProcessors options can be set via the HTML Library Manager OSGi configuration (in the /system/console/configMgr UI).

For example, to use YUI compressor for css minification and Google Closure Compiler for JS set these properties on the cq:ClientLibraryFolder node: 

cssProcessor: ["default:none", "min:yui"]
jsProcessor: ["default:none", "min:gcc;compilationLevel=advanced"]
use typescript to preprocess, then gcc to minify and obfuscate:
jsProcessor: [
   "default:typescript",
   "min:typescript", 
   "min:gcc;obfuscate=true"
]

the format is: 

config:= mode ":" processorName options*;
mode:= "default" | "min";
processorName := "none" | ;
options := ";" option;
option := name "=" value;

• failOnWarning (defaults to "false")
• languageIn (defaults to "ECMASCRIPT5")
• languageOut (defaults to "ECMASCRIPT5")
• compilationLevel (defaults to "simple") (can be "whitespace", "simple", "advanced")