UnderscoreJS 1.2.4 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 35286 bytes (34.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12203 bytes (11.9k, 35%).

After GZIP compression these minified files vary in size:

Boot	4623 bytes (4.5k)	CDN
Baidu	4152 bytes (4.1k)	CDN
gzip -6 (default)	4141 bytes (4.0k)	local copy
gzip -9	4133 bytes (4.0k)	local copy
cdnjs	4129 bytes (4.0k)	CDN
unpkg	4123 bytes (4.0k)	CDN
libdeflate -12	4025 bytes (3.9k)	local copy
7zip -mx=9 -tgzip	4021 bytes (3.9k)	local copy
kzip -s0 -rn -b1	4019 bytes (3.9k)	local copy
zultra	4017 bytes (3.9k)	local copy
pigz -11 -n	4010 bytes (3.9k)	local copy
Zopfli	4004 bytes (3.9k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.4.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.2.4 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 119 bytes by using my UnderscoreJS 1.2.4 Zopfli version instead of the best available CDN (2.97% smaller than unpkg, 4004 vs. 4123 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 --i100000 --mb8 --mls1024 --bsr10 --lazy --ohh

(found February 12, 2019)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
block splitting recursion	10	--bsr10
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/1.2.4/underscore-min.js --location | md5sum
ba6fafc612bc3d089d76072aa4c6198f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.4.min.zopfli.js.gz | md5sum
ba6fafc612bc3d089d76072aa4c6198f -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.2.4/underscore-min.js --location | sha1sum
63f6a94752e5fde78627529763e67ecd4ef78f12 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.4.min.zopfli.js.gz | sha1sum
63f6a94752e5fde78627529763e67ecd4ef78f12 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4623 bytes	ba6fafc612bc3d089d76072aa4c6198f	(invalid)
cdnjs	4129 bytes	ba6fafc612bc3d089d76072aa4c6198f	(invalid)
unpkg	4123 bytes	ba6fafc612bc3d089d76072aa4c6198f	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4152 bytes	e74af9e87325f5617c1aae48768eb6fa	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
4004 bytes	-1 byte	zopfli --i100000 --mls1024 --bsr10 --lazy --ohh	February 12, 2019 @ 21:42
4005 bytes	-1 byte	zopfli --i10000 --mls1024 --bsr8 --lazy --ohh	September 8, 2015 @ 15:50
4006 bytes	-1 byte	zopfli --i1000 --mls1024 --bsr8 --lazy --ohh	September 8, 2015 @ 10:57
4007 bytes	–	zopfli --i100 --mls1024 --bsr6 --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 @ 12:49.

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	4009	4009	4009	4013	4014	4013	4015	4013	4013	4013	4020	4008	4009	4009	4009
4	4009	4009	4008	4008	4008	4009	4005	4013	4008	4006	4006	4006	4005	4005	4005
6	4009	4009	4008	4007	4008	4007	4008	4008	4007	4005	4007	4004	4006	4005	4005
7	4008	4008	4009	4008	4007	4008	4004	4006	4006	4006	4005	4005	4009	4008	4008
8	4009	4009	4007	4007	4008	4008	4007	4008	4008	4005	4006	4007	4006	4005	4005
9	4009	4009	4008	4007	4007	4009	4007	4013	4009	4007	4005	4007	4009	4008	4008
10	4009	4009	4007	4007	4007	4008	4004	4008	4008	4004	4007	4005	4009	4005	4005
11	4009	4009	4007	4007	4007	4008	4004	4008	4008	4006	4005	4005	4009	4005	4005
12	4008	4008	4009	4008	4007	4008	4010	4014	4008	4007	4005	4005	4006	4006	4006
13	4009	4009	4006	4007	4007	4008	4004	4008	4007	4005	4006	4005	4006	4006	4006
14	4009	4009	4010	4007	4007	4008	4005	4008	4008	4005	4006	4005	4005	4006	4006
15	4009	4009	4008	4008	4008	4008	4005	4008	4008	4008	4006	4005	4006	4009	4009
16	4009	4009	4007	4007	4008	4008	4007	4008	4007	4007	4006	4008	4009	4009	4009
17	4009	4009	4007	4007	4010	4008	4007	4008	4008	4007	4005	4005	4005	4005	4005
18	4009	4009	4009	4008	4008	4009	4004	4008	4007	4008	4005	4008	4005	4008	4008
19	4009	4009	4006	4007	4010	4008	4004	4013	4011	4006	4007	4005	4005	4005	4005
20	4009	4009	4007	4007	4008	4009	4009	4008	4008	4008	4006	4005	4004	4005	4005
21	4009	4009	4009	4007	4007	4008	4005	4008	4008	4006	4013	4005	4004	4004	4004
22	4009	4009	4009	4007	4010	4008	4005	4014	4008	4005	4013	4005	4006	4006	4006
23	4009	4009	4007	4007	4008	4008	4008	4008	4007	4008	4008	4006	4006	4006	4006
25	4008	4008	4010	4008	4007	4007	4005	4008	4007	4006	4006	4005	4006	4006	4006
30	4009	4009	4007	4008	4008	4008	4005	4008	4008	4006	4007	4005	4006	4006	4006
40	4009	4009	4007	4007	4007	4009	4007	4008	4008	4005	4006	4005	4009	4009	4009

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	4007 bytes	–	100%
1,000	4006 bytes	-1 byte	100%
10,000	4005 bytes	-1 byte	100%
100,000	4004 bytes	-1 byte	19.42%
1,000,000	4004 bytes	–	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)	4019 bytes	+15 bytes (+0.37%)	–
1	4019 bytes	+15 bytes (+0.37%)	–
2	4039 bytes	+35 bytes (+0.87%)	+20 bytes
3	4035 bytes	+31 bytes (+0.77%)	+16 bytes
4	4071 bytes	+67 bytes (+1.67%)	+52 bytes
5	4093 bytes	+89 bytes (+2.22%)	+74 bytes
6	4125 bytes	+121 bytes (+3.02%)	+106 bytes
7	4151 bytes	+147 bytes (+3.67%)	+132 bytes
8	4184 bytes	+180 bytes (+4.50%)	+165 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	3588 bytes	-416 bytes (-10.39%)
Brotli (Wikipedia)	brotli	brotli -q 11	3691 bytes	-313 bytes (-7.82%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3957 bytes	-47 bytes (-1.17%)
Zstandard (Wikipedia)	zstd	zstd -19	4038 bytes	+34 bytes (+0.85%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4048 bytes	+44 bytes (+1.10%)
LZMA2 (Wikipedia)	xz	xz -9	4100 bytes	+96 bytes (+2.40%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4440 bytes	+436 bytes (+10.89%)

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.