UnderscoreJS 0.4.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 18316 bytes (17.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 6892 bytes (6.7k, 38%).

After GZIP compression these minified files vary in size:

Boot	2477 bytes (2.4k)	CDN
gzip -9	2251 bytes (2.2k)	local copy
gzip -6 (default)	2250 bytes (2.2k)	local copy
Baidu	2236 bytes (2.2k)	CDN
cdnjs	2236 bytes (2.2k)	CDN
7zip -mx=9 -tgzip	2184 bytes (2.1k)	local copy
libdeflate -12	2184 bytes (2.1k)	local copy
kzip -s0 -rn -b1	2182 bytes (2.1k)	local copy
zultra	2180 bytes (2.1k)	local copy
pigz -11 -n	2179 bytes (2.1k)	local copy
Zopfli	2177 bytes (2.1k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.4.1 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 59 bytes by using my UnderscoreJS 0.4.1 Zopfli version instead of the best available CDN (2.71% smaller than cdnjs, 2177 vs. 2236 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 --mls64 --bsr8 --lazy --ohh

(found March 4, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	64	--mls64
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/0.4.1/underscore-min.js --location | md5sum
917b0d296f09ba7e360e4648bd91d716 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.1.min.zopfli.js.gz | md5sum
917b0d296f09ba7e360e4648bd91d716 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.4.1/underscore-min.js --location | sha1sum
63b93c2e3fbc194ef03d22588b63d15375455c62 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.1.min.zopfli.js.gz | sha1sum
63b93c2e3fbc194ef03d22588b63d15375455c62 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2477 bytes	917b0d296f09ba7e360e4648bd91d716	(invalid)
Baidu	2236 bytes	917b0d296f09ba7e360e4648bd91d716	(invalid)
cdnjs	2236 bytes	917b0d296f09ba7e360e4648bd91d716	(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
2177 bytes	-1 byte	zopfli --i1000000 --mls64 --bsr8 --lazy --ohh	March 4, 2020 @ 10:53
2178 bytes	-1 byte	zopfli --i10000 --mls64 --bsr8 --lazy --ohh	February 2, 2016 @ 23:06
2179 bytes	–	zopfli --i100 --mls32768 --bsr15 --lazy --ohh	February 2, 2016 @ 20:57

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 @ 12:51.

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	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
4	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
6	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
7	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
8	2178	2178	2178	2179	2178	2177	2178	2178	2178	2178	2178	2178	2178	2178	2178
9	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
10	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
11	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
12	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
13	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
14	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
15	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
16	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
17	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
18	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
19	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
20	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
21	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
22	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
23	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
25	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
30	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178
40	2178	2178	2178	2179	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178	2178

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	2179 bytes	–	100%
1,000	2179 bytes	–	100%
10,000	2178 bytes	-1 byte	100%
100,000	2178 bytes	–	93.33%
1,000,000	2177 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)	2182 bytes	+5 bytes (+0.23%)	–
1	2182 bytes	+5 bytes (+0.23%)	–
2	2208 bytes	+31 bytes (+1.42%)	+26 bytes
3	2234 bytes	+57 bytes (+2.62%)	+52 bytes
4	2266 bytes	+89 bytes (+4.09%)	+84 bytes
5	2293 bytes	+116 bytes (+5.33%)	+111 bytes
6	2313 bytes	+136 bytes (+6.25%)	+131 bytes
7	2344 bytes	+167 bytes (+7.67%)	+162 bytes
8	2379 bytes	+202 bytes (+9.28%)	+197 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	1959 bytes	-218 bytes (-10.01%)
Brotli (Wikipedia)	brotli	brotli -q 11	1982 bytes	-195 bytes (-8.96%)
Zstandard (Wikipedia)	zstd	zstd -19	2200 bytes	+23 bytes (+1.06%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2243 bytes	+66 bytes (+3.03%)
LZMA2 (Wikipedia)	xz	xz -9	2264 bytes	+87 bytes (+4.00%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2392 bytes	+215 bytes (+9.88%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	2866 bytes	+689 bytes (+31.65%)

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.