UnderscoreJS 1.3.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 35099 bytes (34.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12122 bytes (11.8k, 35%).

After GZIP compression these minified files vary in size:

Boot	4577 bytes (4.5k)	CDN
Baidu	4116 bytes (4.0k)	CDN
gzip -6 (default)	4110 bytes (4.0k)	local copy
gzip -9	4103 bytes (4.0k)	local copy
cdnjs	4098 bytes (4.0k)	CDN
unpkg	4090 bytes (4.0k)	CDN
libdeflate -12	3999 bytes (3.9k)	local copy
zultra	3996 bytes (3.9k)	local copy
7zip -mx=9 -tgzip	3994 bytes (3.9k)	local copy
kzip -s0 -rn -b0	3992 bytes (3.9k)	local copy
pigz -11 -n	3985 bytes (3.9k)	local copy
Zopfli	3976 bytes (3.9k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.3.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.3.0 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 114 bytes by using my UnderscoreJS 1.3.0 Zopfli version instead of the best available CDN (2.87% smaller than unpkg, 3976 vs. 4090 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 --mls32 --bsr8 --lazy --ohh

(found February 26, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	32	--mls32
block splitting recursion	8	--bsr8
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/1.3.0/underscore-min.js --location | md5sum
479cbbe3b04152bf4b6c7531f6bf200d -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.3.0.min.zopfli.js.gz | md5sum
479cbbe3b04152bf4b6c7531f6bf200d -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.3.0/underscore-min.js --location | sha1sum
86752ba2e4f3855a8a5e45d5f07567ea70a9cc98 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.3.0.min.zopfli.js.gz | sha1sum
86752ba2e4f3855a8a5e45d5f07567ea70a9cc98 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4577 bytes	479cbbe3b04152bf4b6c7531f6bf200d	(invalid)
cdnjs	4098 bytes	479cbbe3b04152bf4b6c7531f6bf200d	(invalid)
unpkg	4090 bytes	479cbbe3b04152bf4b6c7531f6bf200d	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4116 bytes	657ef8f863a48206d0ce87e73c7ca333	only whitespaces differ	(invalid)

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
3976 bytes	-1 byte	zopfli --i1000000 --mls32 --bsr8 --lazy --ohh	February 26, 2020 @ 15:19
3977 bytes	-1 byte	zopfli --i10000 --mls32 --bsr8 --lazy --ohh	November 20, 2015 @ 16:56
3978 bytes	-1 byte	zopfli --i1000 --mls8192 --bsr2 --lazy --ohh	September 8, 2015 @ 10:57
3979 bytes	-1 byte	zopfli --i1000 --mls512 --bsr8 --lazy --ohh	September 8, 2015 @ 10:56
3980 bytes	–	zopfli --i100 --mls4096 --bsr16 --lazy --ohh	September 8, 2015 @ 10:32

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 @ 12:55.

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	3982	3982	3984	3982	3982	3982	3984	3983	3982	3982	3982	3979	3978	3978	3978
4	3978	3978	3978	3978	3979	3982	3980	3979	3989	3983	3982	3978	3981	3978	3978
6	3984	3984	3978	3978	3980	3980	3979	3979	3978	3980	3980	3978	3979	3978	3978
7	3979	3979	3979	3979	3978	3978	3984	3979	3978	3980	3982	3980	3978	3978	3978
8	3979	3979	3978	3978	3976	3982	3981	3978	3978	3980	3982	3978	3978	3978	3978
9	3978	3978	3978	3978	3985	3979	3979	3980	3978	3980	3980	3980	3979	3978	3978
10	3978	3978	3991	3978	3982	3981	3981	3978	3979	3980	3982	3981	3978	3978	3978
11	3978	3978	3978	3978	3978	3981	3979	3978	3978	3981	3980	3981	3981	3979	3979
12	3979	3979	3979	3978	3979	3979	3978	3978	3978	3981	3980	3978	3978	3978	3978
13	3979	3979	3979	3978	3979	3980	3979	3978	3978	3980	3980	3982	3981	3979	3979
14	3979	3979	3979	3992	3978	3982	3982	3979	3989	3980	3982	3981	3978	3979	3979
15	3978	3978	3978	3979	3977	3982	3984	3979	3978	3982	3982	3979	3978	3978	3978
16	3978	3978	3978	3978	3980	3982	3981	3978	3978	3980	3980	3978	3980	3979	3979
17	3979	3979	3984	3978	3985	3979	3984	3978	3979	3980	3980	3981	3978	3978	3978
18	3979	3979	3978	3978	3978	3981	3979	3978	3978	3980	3982	3980	3978	3980	3980
19	3978	3978	3978	3978	3978	3978	3982	3978	3978	3980	3980	3980	3981	3980	3980
20	3978	3978	3978	3985	3984	3984	3979	3978	3978	3980	3980	3978	3979	3980	3980
21	3978	3978	3978	3978	3978	3978	3982	3978	3978	3980	3982	3980	3979	3980	3980
22	3978	3978	3978	3978	3978	3978	3982	3978	3978	3980	3980	3980	3981	3980	3980
23	3978	3978	3978	3978	3978	3979	3982	3978	3978	3980	3982	3980	3978	3978	3978
25	3984	3984	3985	3985	3979	3979	3982	3978	3978	3980	3981	3978	3978	3978	3978
30	3979	3979	3978	3979	3979	3985	3981	3979	3978	3981	3982	3978	3982	3978	3978
40	3979	3979	3979	3978	3979	3978	3982	3979	3979	3980	3980	3980	3981	3978	3978

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	3979 bytes	–	100%
1,000	3978 bytes	-1 byte	100%
10,000	3977 bytes	-1 byte	100%
100,000	3977 bytes	–	0.58%
1,000,000	3976 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)	3992 bytes	+16 bytes (+0.40%)	–
1	3993 bytes	+17 bytes (+0.43%)	+1 byte
2	4010 bytes	+34 bytes (+0.86%)	+18 bytes
3	4007 bytes	+31 bytes (+0.78%)	+15 bytes
4	4041 bytes	+65 bytes (+1.63%)	+49 bytes
5	4066 bytes	+90 bytes (+2.26%)	+74 bytes
6	4097 bytes	+121 bytes (+3.04%)	+105 bytes
7	4124 bytes	+148 bytes (+3.72%)	+132 bytes
8	4158 bytes	+182 bytes (+4.58%)	+166 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	3557 bytes	-419 bytes (-10.54%)
Brotli (Wikipedia)	brotli	brotli -q 11	3655 bytes	-321 bytes (-8.07%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3943 bytes	-33 bytes (-0.83%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4014 bytes	+38 bytes (+0.96%)
Zstandard (Wikipedia)	zstd	zstd -19	4014 bytes	+38 bytes (+0.96%)
LZMA2 (Wikipedia)	xz	xz -9	4068 bytes	+92 bytes (+2.31%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4418 bytes	+442 bytes (+11.12%)

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.