Compress matomo.js via Closure Compiler instead of YUI Compressor

[rr-it]

Summary

The use of Closure Compiler (CC) has some benefits over YUI Compressor (YUI).

Sligtly smaller file size

• piwik.js minified: CC 51.8 KB vs. YUI 66.3 KB
• piwik.js minified and gzipped: CC 18.9 KB vs. YUI 21.5 KB

Sligtly better performance of generated JS-code

CC optimises the generated JS-code with multiple performance tweaks:

• runs faster in browser
• is better compressable by gzip (e.g. CC implements optimisations to achieve gains on the Huffman encoding)

Error and Warning reports on JS code smells and errors

CC gives feedback on JS code smells and errors. See all the annotations that are suppressable.

CC can enforce ECMAScript: ECMA-262, edition 3 and thereby ensures Browser Compatibility:
java -jar closure-compiler-v20230502.jar --language_in ECMASCRIPT3 --language_out ECMASCRIPT3

Munging of private object property names

CC also munges object property names.

E.g. findContentNodesWithinNode is only used internaly inside the closure function.

var content = {
    findContentNodesWithinNode: function (node) {…}
}

The call content.findContentNodesWithinNode(domNode) becomes:

• CC: a.Bb(z)
• YUI: a.findContentNodesWithinNode(z)

Munging of all function names (PRO & CON)

By default CC munges really all function names - and thereby also the public Tracking API names.

The munging of public function names is prevented by an extra JS-file containing an @externs annotation and the function definitions.

• CON: externs-definitions must be created and maintained.
• PRO: externs-definitions are created and maintained. Thereby we get a technical approach to define the public API.

See Closure Compiler: Externs and Exports

Munging of all property names in data-objects (CON)

CC munges all property names. All call-parameters that must not be changed, must be in proper quotes.

callback({request: request, trackerUrl: configTrackerUrl, success: false, xhr: this});

/* CC minified: property names changed. */
a({Ba: Cu, Bb: Cv, Bc: !1, Bd: this});

callback({'request': request, 'trackerUrl': configTrackerUrl, 'success': false, 'xhr': this});

/* CC minified: property names unchanged. */
a({request: Cu, trackerUrl: Cv, success: !1, xhr: this});

See Closure Compiler: Restrictions for ADVANCED_OPTIMIZATIONS

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Related to

• Use maintained JS minifier #15412
• QA: run Javascript tests on both the original and minified JS #5165