UnderscoreJS 1.2.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 33068 bytes (32.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 11383 bytes (11.1k, 34%).

After GZIP compression these minified files vary in size:

Boot	4360 bytes (4.3k)	CDN
Baidu	3923 bytes (3.8k)	CDN
gzip -6 (default)	3909 bytes (3.8k)	local copy
gzip -9	3909 bytes (3.8k)	local copy
unpkg	3906 bytes (3.8k)	CDN
cdnjs	3903 bytes (3.8k)	CDN
7zip -mx=9 -tgzip	3821 bytes (3.7k)	local copy
libdeflate -12	3820 bytes (3.7k)	local copy
zultra	3815 bytes (3.7k)	local copy
kzip -s0 -rn -b0	3812 bytes (3.7k)	local copy
pigz -11 -n	3806 bytes (3.7k)	local copy
Zopfli	3800 bytes (3.7k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.2.0 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 103 bytes by using my UnderscoreJS 1.2.0 Zopfli version instead of the best available CDN (2.71% smaller than cdnjs, 3800 vs. 3903 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 --mls8192 --bsr11 --lazy --ohh

(found February 8, 2019)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	8192	--mls8192
block splitting recursion	11	--bsr11
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/1.2.0/underscore-min.js --location | md5sum
e60157694a7ce538626c645dfd910533 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.0.min.zopfli.js.gz | md5sum
e60157694a7ce538626c645dfd910533 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.2.0/underscore-min.js --location | sha1sum
7d6e352b0d26655ba851863561b5d912cc24caa7 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.0.min.zopfli.js.gz | sha1sum
7d6e352b0d26655ba851863561b5d912cc24caa7 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4360 bytes	e60157694a7ce538626c645dfd910533	(invalid)
unpkg	3906 bytes	e60157694a7ce538626c645dfd910533	July 11, 2016 @ 16:49
cdnjs	3903 bytes	e60157694a7ce538626c645dfd910533	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	3923 bytes	f13031440fe4a2fc36d57a76d9fb395c	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
3800 bytes	-1 byte	zopfli --i100000 --mls8192 --bsr11 --lazy --ohh	February 8, 2019 @ 15:23
3801 bytes	-1 byte	zopfli --i1000 --mls8192 --bsr11 --lazy --ohh	September 8, 2015 @ 11:01
3802 bytes	–	zopfli --i100 --mls1024 --bsr11 --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 @ 12:52.

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	3808	3808	3807	3808	3810	3810	3809	3809	3810	3810	3808	3808	3806	3806	3806
4	3802	3802	3802	3802	3803	3801	3802	3802	3802	3802	3804	3802	3802	3803	3803
6	3804	3804	3804	3805	3802	3802	3802	3802	3802	3802	3802	3803	3800	3800	3800
7	3806	3806	3803	3805	3800	3802	3803	3802	3802	3802	3802	3803	3801	3802	3802
8	3805	3805	3801	3803	3800	3802	3802	3804	3802	3801	3804	3802	3800	3800	3800
9	3802	3802	3805	3803	3802	3802	3802	3802	3802	3802	3800	3803	3800	3802	3802
10	3804	3804	3802	3803	3803	3802	3802	3805	3801	3802	3801	3801	3800	3802	3802
11	3807	3807	3801	3802	3800	3805	3809	3802	3801	3801	3804	3801	3800	3802	3802
12	3805	3805	3802	3802	3801	3811	3809	3809	3808	3802	3808	3801	3802	3802	3802
13	3801	3801	3802	3803	3803	3802	3802	3802	3802	3802	3802	3802	3801	3802	3802
14	3809	3809	3804	3804	3800	3802	3802	3802	3802	3802	3800	3802	3800	3800	3800
15	3807	3807	3802	3804	3801	3806	3809	3804	3809	3802	3804	3803	3801	3800	3800
16	3800	3800	3802	3802	3802	3802	3803	3802	3801	3801	3801	3802	3800	3802	3802
17	3805	3805	3801	3805	3800	3802	3802	3802	3802	3801	3801	3801	3802	3800	3800
18	3805	3805	3801	3802	3800	3802	3802	3802	3801	3805	3804	3801	3800	3800	3800
19	3800	3800	3803	3802	3800	3802	3802	3802	3801	3801	3802	3801	3800	3800	3800
20	3800	3800	3803	3804	3800	3802	3802	3802	3801	3801	3800	3804	3800	3800	3800
21	3800	3800	3801	3802	3802	3802	3802	3802	3801	3801	3804	3801	3800	3803	3803
22	3800	3800	3803	3802	3803	3808	3809	3802	3802	3802	3803	3803	3800	3802	3802
23	3805	3805	3804	3805	3803	3802	3802	3802	3800	3802	3804	3802	3801	3802	3802
25	3804	3804	3802	3802	3802	3802	3802	3802	3802	3801	3804	3802	3802	3802	3802
30	3803	3803	3801	3803	3802	3802	3802	3802	3800	3802	3802	3802	3800	3802	3802
40	3800	3800	3802	3802	3802	3802	3802	3802	3802	3802	3804	3801	3802	3803	3803

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	3802 bytes	–	100%
1,000	3801 bytes	-1 byte	100%
10,000	3801 bytes	–	100%
100,000	3800 bytes	-1 byte	27.54%
1,000,000	3800 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)	3812 bytes	+12 bytes (+0.32%)	–
1	3812 bytes	+12 bytes (+0.32%)	–
2	3835 bytes	+35 bytes (+0.92%)	+23 bytes
3	3839 bytes	+39 bytes (+1.03%)	+27 bytes
4	3858 bytes	+58 bytes (+1.53%)	+46 bytes
5	3890 bytes	+90 bytes (+2.37%)	+78 bytes
6	3919 bytes	+119 bytes (+3.13%)	+107 bytes
7	3954 bytes	+154 bytes (+4.05%)	+142 bytes
8	3985 bytes	+185 bytes (+4.87%)	+173 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	3426 bytes	-374 bytes (-9.84%)
Brotli (Wikipedia)	brotli	brotli -q 11	3494 bytes	-306 bytes (-8.05%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3803 bytes	+3 bytes (+0.08%)
Zstandard (Wikipedia)	zstd	zstd -19	3829 bytes	+29 bytes (+0.76%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	3873 bytes	+73 bytes (+1.92%)
LZMA2 (Wikipedia)	xz	xz -9	3896 bytes	+96 bytes (+2.53%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4285 bytes	+485 bytes (+12.76%)

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.