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Thread: DEFLATE-ing popular Javascript libraries

  1. #1
    Join Date
    Mar 2013
    Thanked 79 Times in 33 Posts

    DEFLATE-ing popular Javascript libraries

    About two out of three major websites are based on the jQuery Javascript library. jQuery 2.1.4 weights about 250kb and code minification brings it down to 82kb. GZIP compression reduces the number of bytes to be transferred to 34418 bytes (official download at

    I was surprised to find that a simple gzip -9 produced a significantly smaller file (29539 bytes). Since jQuery is pretty much a textbook example of "compress once, decompress a gazillion times", I started to play around with various DEFLATE encoders. My intention was to spend tons of CPU cycles while compressing in order to save every byte possible.

    Google's Zopfli, especially Krzymod's fork, produces the best results, which can be found here: kzip and 7zip are included in my tests as well.

    These promising numbers gave me a push to include older jQuery versions as well as other popular Javascript libraries, such as AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, Knockout, React and UnderscoreJS. Go to to get more details.

    Moreover, I downloaded these libraries from their original websites and from major public content delivery networks like Google, Microsoft, cdnJS, jsdelivr, Yandex and Boot. With a few exceptions they all fail to be even comparable to gzip -9. I have no idea why because smaller files would directly lead to reduced network costs.

    For those who feel the urgent need to take a peek inside these compressed files, I wrote a simple DEFLATE decompressor in Javascript which visualized the Huffman tables and LZ77 matches of the smallest GZIPped files (scroll down to the bottom of the page to the "Detailled Analysis" and press the button "Load and Parse Data").

  2. Thanks (3):

    Cyan (31st January 2016),Jyrki Alakuijala (31st January 2016),Mr_KrzYch00 (30th January 2016)

  3. #2
    Member Mr_KrzYch00's Avatar
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    Apr 2015
    Thanked 40 Times in 24 Posts
    I'm amazed with Your work. :)

    I noticed that Zopfli resumed developing process, however, those changes are not yet up in KrzYmod fork as I have no time to manually merge so many changes at the moment, neither to even compile original project.

    I wonder if those latest changes improve compression with original zopfli. hmm.

    * KrzYmod is the name for the fork I have chosen to use, so for the sake of correctness, it should be called Mr_KrzYch00's Zopfli fork, aka. Zopfli "KrzYmod" :)

    EDIT: Ah yes, I forgot to mention. You could still get better results with Zopfli "KrzYmod" fork when using --cbs command to finetune block splitting point(s). That would certainly give different results. Back when I was doing my tests, sometimes using kzip split points with zopfli compression algorithm provided better results than using other various Zopfli settings alone.
    Last edited by Mr_KrzYch00; 30th January 2016 at 22:24.

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