UnderscoreJS 1.8.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 52374 bytes (51.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 16523 bytes (16.1k, 32%).

After GZIP compression these minified files vary in size:

Boot	6561 bytes (6.4k)	CDN
jsdelivr	6561 bytes (6.4k)	CDN
cdnjs	5850 bytes (5.7k)	CDN
gzip -6 (default)	5846 bytes (5.7k)	local copy
gzip -9	5829 bytes (5.7k)	local copy
unpkg	5815 bytes (5.7k)	CDN
Yandex	5807 bytes (5.7k)	CDN
libdeflate -12	5658 bytes (5.5k)	local copy
7zip -mx=9 -tgzip	5653 bytes (5.5k)	local copy
kzip -s0 -rn -b1	5643 bytes (5.5k)	local copy
zultra	5642 bytes (5.5k)	local copy
pigz -11 -n	5641 bytes (5.5k)	local copy
Zopfli	5628 bytes (5.5k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.8.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.8.2 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

Save 179 bytes by using my UnderscoreJS 1.8.2 Zopfli version instead of the best available CDN (3.18% smaller than Yandex, 5628 vs. 5807 bytes):

Download

You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i1000000 --mb8 --mls1024 --bsr16 --lazy --ohh

(found March 2, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
block splitting recursion	16	--bsr16
lazy matching in LZ77	yes	--lazy
optimized Huffman headers	yes	--ohh
initial random W for iterations	1	--rw1
initial random Z for iterations	2	--rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.8.2/underscore-min.js --location | md5sum
b0e9839a6bb6f12774494fa30c06bcdf -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.8.2.min.zopfli.js.gz | md5sum
b0e9839a6bb6f12774494fa30c06bcdf -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.8.2/underscore-min.js --location | sha1sum
e686abc5c68dfaf7a14ce3dc68e33703750bc901 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.8.2.min.zopfli.js.gz | sha1sum
e686abc5c68dfaf7a14ce3dc68e33703750bc901 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	6561 bytes	b0e9839a6bb6f12774494fa30c06bcdf	(invalid)
jsdelivr	6561 bytes	b0e9839a6bb6f12774494fa30c06bcdf	(invalid)
cdnjs	5850 bytes	b0e9839a6bb6f12774494fa30c06bcdf	(invalid)
unpkg	5815 bytes	b0e9839a6bb6f12774494fa30c06bcdf	July 11, 2016 @ 16:48
Yandex	5807 bytes	b0e9839a6bb6f12774494fa30c06bcdf	December 22, 2015 @ 17:09

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available UnderscoreJS versions at minime.stephan-brumme.com:

1.13.6, 1.13.5, 1.13.4, 1.13.3, 1.13.2, 1.13.1, 1.13.0,
1.12.1, 1.12.0,
1.11.0,
1.10.2, 1.10.1, 1.10.0,
1.9.2, 1.9.1, 1.9.0,
1.8.3, 1.8.2, 1.8.1,
1.7.0,
1.6.0,
1.5.2, 1.5.0,
1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0,
1.3.3, 1.3.2, 1.3.1, 1.3.0,
1.2.4, 1.2.3, 1.2.2, 1.2.1, 1.2.0,
1.1.7, 1.1.5, 1.1.4, 1.1.3, 1.1.2, 1.1.1, 1.1.0,
1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0.0,
0.6.0,
0.5.7, 0.5.6, 0.5.5, 0.5.4, 0.5.3, 0.5.2, 0.5.1, 0.5.0,
0.4.7, 0.4.6, 0.4.5, 0.4.4, 0.4.3, 0.4.2, 0.4.1, 0.4.0,
0.3.3, 0.3.2, 0.3.1, 0.3.0,
0.2.0,
0.1.1, 0.1.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
5628 bytes	-1 byte	zopfli --i1000000 --mls1024 --bsr16 --lazy --ohh	March 2, 2020 @ 10:19
5629 bytes	-1 byte	zopfli --i100000 --mls1024 --bsr16 --lazy --ohh	September 8, 2015 @ 18:51
5630 bytes	-1 byte	zopfli --i10000 --mls1024 --bsr16 --lazy --ohh	September 8, 2015 @ 11:09
5631 bytes	-1 byte	zopfli --i1000 --mls1024 --bsr16 --lazy --ohh	September 8, 2015 @ 10:38
5632 bytes	–	zopfli --i100 --mls8192 --bsr8 --lazy --ohh	September 8, 2015 @ 10:34

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on July 20, 2020 @ 12:56.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000, 100,000 or 1,000,000.

bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
2	5640	5633	5640	5632	5640	5636	5635	5631	5630	5640	5640	5639	5633	5635	5635
4	5647	5647	5647	5635	5640	5640	5636	5636	5631	5640	5640	5637	5638	5638	5638
6	5646	5632	5646	5648	5640	5636	5636	5635	5630	5630	5640	5637	5637	5638	5638
7	5635	5635	5647	5634	5640	5640	5636	5630	5631	5632	5640	5638	5631	5638	5638
8	5633	5633	5636	5634	5640	5635	5636	5631	5631	5630	5640	5637	5630	5632	5632
9	5647	5647	5647	5635	5648	5640	5636	5635	5631	5640	5640	5634	5637	5638	5638
10	5648	5647	5636	5634	5647	5635	5629	5636	5630	5640	5640	5638	5637	5638	5638
11	5633	5633	5636	5634	5640	5640	5636	5631	5631	5630	5640	5635	5635	5638	5638
12	5646	5646	5647	5634	5640	5635	5636	5636	5635	5640	5640	5635	5630	5632	5632
13	5648	5647	5647	5634	5640	5635	5636	5630	5630	5630	5640	5636	5629	5637	5637
14	5647	5646	5646	5635	5640	5636	5636	5631	5631	5631	5640	5637	5637	5638	5638
15	5634	5634	5646	5634	5640	5635	5636	5630	5631	5632	5640	5638	5638	5638	5638
16	5646	5646	5647	5634	5640	5636	5636	5637	5631	5628	5640	5637	5629	5638	5638
17	5647	5646	5636	5634	5640	5635	5636	5630	5636	5629	5640	5638	5631	5632	5632
18	5634	5634	5647	5634	5648	5635	5636	5630	5633	5629	5640	5639	5631	5637	5637
19	5635	5634	5636	5635	5640	5636	5636	5634	5636	5632	5640	5636	5638	5638	5638
20	5646	5646	5647	5634	5647	5631	5636	5631	5631	5630	5640	5638	5638	5638	5638
21	5647	5646	5636	5647	5640	5635	5636	5636	5631	5630	5640	5638	5638	5638	5638
22	5646	5646	5647	5634	5640	5635	5636	5630	5632	5632	5640	5636	5638	5638	5638
23	5634	5634	5647	5634	5647	5635	5636	5634	5637	5640	5640	5638	5631	5638	5638
25	5646	5646	5646	5634	5640	5635	5636	5636	5632	5631	5640	5636	5638	5637	5637
30	5645	5647	5647	5635	5647	5635	5636	5637	5636	5631	5640	5638	5638	5638	5638
40	5647	5647	5646	5635	5648	5631	5636	5637	5632	5632	5640	5637	5636	5638	5638

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:

Iterations	Min. Bytes	Reduction	Coverage
100	5632 bytes	–	100%
1,000	5631 bytes	-1 byte	100%
10,000	5629 bytes	-2 bytes	100%
100,000	5629 bytes	–	16.81%
1,000,000	5628 bytes	-1 byte	0.29%
10,000,000	–	–	–

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):

Blocks	Min. Bytes	Compared To Best Zopfli	Compared To Best KZIP
(any)	5643 bytes	+15 bytes (+0.27%)	–
1	5643 bytes	+15 bytes (+0.27%)	–
2	5664 bytes	+36 bytes (+0.64%)	+21 bytes
3	5698 bytes	+70 bytes (+1.24%)	+55 bytes
4	5721 bytes	+93 bytes (+1.65%)	+78 bytes
5	5729 bytes	+101 bytes (+1.79%)	+86 bytes
6	5767 bytes	+139 bytes (+2.47%)	+124 bytes
7	5798 bytes	+170 bytes (+3.02%)	+155 bytes
8	5830 bytes	+202 bytes (+3.59%)	+187 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - for example, your browser actually supports it !

Algorithm	Program	Parameters	Size	Compared To Best Zopfli
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	4955 bytes	-673 bytes (-11.96%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	5192 bytes	-436 bytes (-7.75%)
Brotli (Wikipedia)	brotli	brotli -q 11	5262 bytes	-366 bytes (-6.50%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	5553 bytes	-75 bytes (-1.33%)
Zstandard (Wikipedia)	zstd	zstd -19	5649 bytes	+21 bytes (+0.37%)
LZMA2 (Wikipedia)	xz	xz -9	5696 bytes	+68 bytes (+1.21%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	5751 bytes	+123 bytes (+2.19%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):

Load and Parse Data

Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2026.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com

All trademarks are property of their respective owners. You know, the boring legal stuff.