UnderscoreJS 1.2.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 34498 bytes (33.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 11911 bytes (11.6k, 35%).

After GZIP compression these minified files vary in size:

Boot	4531 bytes (4.4k)	CDN
Baidu	4067 bytes (4.0k)	CDN
gzip -6 (default)	4052 bytes (4.0k)	local copy
gzip -9	4046 bytes (4.0k)	local copy
cdnjs	4045 bytes (4.0k)	CDN
unpkg	4032 bytes (3.9k)	CDN
libdeflate -12	3945 bytes (3.9k)	local copy
7zip -mx=9 -tgzip	3938 bytes (3.8k)	local copy
kzip -s0 -rn -b0	3938 bytes (3.8k)	local copy
zultra	3938 bytes (3.8k)	local copy
pigz -11 -n	3931 bytes (3.8k)	local copy
Zopfli	3924 bytes (3.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.2.2 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 108 bytes by using my UnderscoreJS 1.2.2 Zopfli version instead of the best available CDN (2.75% smaller than unpkg, 3924 vs. 4032 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 --bsr9 --lazy --ohh

(found February 25, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
block splitting recursion	9	--bsr9
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/1.2.2/underscore-min.js --location | md5sum
f0be4eb0429e119c9d369e6ec2ac5f08 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.2.min.zopfli.js.gz | md5sum
f0be4eb0429e119c9d369e6ec2ac5f08 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.2.2/underscore-min.js --location | sha1sum
1185da1043863517c6aa0a4e0a3bc433dfb98313 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.2.min.zopfli.js.gz | sha1sum
1185da1043863517c6aa0a4e0a3bc433dfb98313 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4531 bytes	f0be4eb0429e119c9d369e6ec2ac5f08	(invalid)
cdnjs	4045 bytes	f0be4eb0429e119c9d369e6ec2ac5f08	(invalid)
unpkg	4032 bytes	f0be4eb0429e119c9d369e6ec2ac5f08	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4067 bytes	aa20654a415040ea0a8146dc0a048aac	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
3924 bytes	-1 byte	zopfli --i1000000 --mls1024 --bsr9 --lazy --ohh	February 25, 2020 @ 19:49
3925 bytes	-1 byte	zopfli --i10000 --mls1024 --bsr9 --lazy --ohh	September 8, 2015 @ 16:03
3926 bytes	-2 bytes	zopfli --i1000 --mls512 --bsr9 --lazy --ohh	September 8, 2015 @ 10:58
3928 bytes	–	zopfli --i100 --mls8192 --bsr12 --lazy --ohh	September 8, 2015 @ 10:33

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 @ 12:47.

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	3930	3930	3931	3930	3930	3930	3932	3942	3942	3929	3930	3931	3930	3929	3929
4	3928	3928	3930	3929	3932	3933	3932	3933	3933	3926	3932	3932	3931	3932	3932
6	3928	3928	3930	3928	3929	3927	3930	3930	3928	3928	3931	3926	3926	3928	3928
7	3933	3933	3930	3927	3932	3932	3928	3934	3927	3927	3926	3926	3927	3927	3927
8	3928	3928	3929	3929	3929	3928	3930	3927	3930	3926	3931	3926	3926	3927	3927
9	3927	3927	3929	3928	3929	3933	3926	3926	3925	3924	3933	3927	3927	3927	3927
10	3942	3942	3927	3926	3932	3929	3928	3926	3926	3926	3926	3926	3927	3927	3927
11	3941	3941	3928	3928	3929	3932	3928	3931	3930	3925	3930	3928	3927	3927	3927
12	3928	3928	3928	3928	3929	3942	3928	3931	3930	3925	3931	3927	3927	3927	3927
13	3928	3928	3930	3929	3929	3929	3929	3928	3928	3927	3927	3926	3927	3927	3927
14	3933	3933	3928	3931	3932	3935	3933	3930	3931	3928	3931	3930	3927	3927	3927
15	3928	3928	3928	3928	3929	3929	3928	3930	3926	3928	3926	3926	3927	3927	3927
16	3928	3928	3928	3928	3929	3932	3927	3927	3928	3926	3927	3927	3927	3927	3927
17	3942	3942	3928	3928	3929	3932	3930	3930	3930	3925	3930	3926	3927	3927	3927
18	3928	3928	3928	3928	3929	3929	3928	3926	3926	3925	3926	3928	3927	3927	3927
19	3928	3928	3928	3928	3932	3931	3928	3926	3926	3925	3930	3926	3927	3927	3927
20	3928	3928	3928	3928	3929	3929	3928	3928	3928	3925	3927	3927	3927	3927	3927
21	3928	3928	3928	3929	3929	3932	3928	3926	3926	3925	3926	3928	3927	3927	3927
22	3928	3928	3928	3933	3929	3932	3928	3930	3930	3927	3930	3928	3925	3926	3926
23	3928	3928	3928	3928	3929	3928	3929	3927	3927	3925	3926	3927	3928	3927	3927
25	3928	3928	3929	3928	3929	3942	3928	3931	3930	3925	3931	3927	3926	3927	3927
30	3928	3928	3928	3929	3929	3929	3930	3926	3926	3925	3931	3926	3927	3927	3927
40	3928	3928	3928	3929	3928	3929	3927	3930	3928	3926	3930	3928	3927	3927	3927

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	3928 bytes	–	100%
1,000	3926 bytes	-2 bytes	100%
10,000	3925 bytes	-1 byte	100%
100,000	3925 bytes	–	3.77%
1,000,000	3924 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)	3938 bytes	+14 bytes (+0.36%)	–
1	3938 bytes	+14 bytes (+0.36%)	–
2	3954 bytes	+30 bytes (+0.76%)	+16 bytes
3	3955 bytes	+31 bytes (+0.79%)	+17 bytes
4	3987 bytes	+63 bytes (+1.61%)	+49 bytes
5	4018 bytes	+94 bytes (+2.40%)	+80 bytes
6	4041 bytes	+117 bytes (+2.98%)	+103 bytes
7	4066 bytes	+142 bytes (+3.62%)	+128 bytes
8	4101 bytes	+177 bytes (+4.51%)	+163 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	3515 bytes	-409 bytes (-10.42%)
Brotli (Wikipedia)	brotli	brotli -q 11	3617 bytes	-307 bytes (-7.82%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3894 bytes	-30 bytes (-0.76%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	3947 bytes	+23 bytes (+0.59%)
Zstandard (Wikipedia)	zstd	zstd -19	3959 bytes	+35 bytes (+0.89%)
LZMA2 (Wikipedia)	xz	xz -9	4016 bytes	+92 bytes (+2.34%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4375 bytes	+451 bytes (+11.49%)

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.