UnderscoreJS 1.9.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 58319 bytes (57.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 18069 bytes (17.6k, 31%).

After GZIP compression these minified files vary in size:

Boot	6617 bytes (6.5k)	CDN
cdnjs	6465 bytes (6.3k)	CDN
gzip -6 (default)	6460 bytes (6.3k)	local copy
gzip -9	6452 bytes (6.3k)	local copy
unpkg	6428 bytes (6.3k)	CDN
7zip -mx=9 -tgzip	6260 bytes (6.1k)	local copy
zultra	6257 bytes (6.1k)	local copy
libdeflate -12	6256 bytes (6.1k)	local copy
kzip -s0 -rn -b0	6252 bytes (6.1k)	local copy
pigz -11 -n	6247 bytes (6.1k)	local copy
Zopfli	6239 bytes (6.1k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.9.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.9.1 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 189 bytes by using my UnderscoreJS 1.9.1 Zopfli version instead of the best available CDN (3.03% smaller than unpkg, 6239 vs. 6428 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 --mls256 --bsr8 --lazy --ohh

(found June 4, 2018)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	256	--mls256
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/1.9.1/underscore-min.js --location | md5sum
66e46fdc840c68d4ba9d8c6bd6ea9cfa -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.9.1.min.zopfli.js.gz | md5sum
66e46fdc840c68d4ba9d8c6bd6ea9cfa -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.9.1/underscore-min.js --location | sha1sum
69b8b33acbd62281920d4b73c310c66c4cfc8992 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.9.1.min.zopfli.js.gz | sha1sum
69b8b33acbd62281920d4b73c310c66c4cfc8992 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	6617 bytes	66e46fdc840c68d4ba9d8c6bd6ea9cfa	June 7, 2018 @ 09:35
cdnjs	6465 bytes	66e46fdc840c68d4ba9d8c6bd6ea9cfa	(invalid)
unpkg	6428 bytes	66e46fdc840c68d4ba9d8c6bd6ea9cfa	(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
6239 bytes	-1 byte	zopfli --i100000 --mls256 --bsr8 --lazy --ohh	June 4, 2018 @ 12:01
6240 bytes	-2 bytes	zopfli --i1000 --mls256 --bsr14 --lazy --ohh	June 4, 2018 @ 09:34
6242 bytes	–	zopfli --i100 --mls1024 --bsr14 --lazy --ohh	June 4, 2018 @ 09:12

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	6251	6251	6260	6251	6251	6251	6251	6249	6251	6251	6251	6242	6251	6250	6250
4	6254	6254	6258	6256	6258	6253	6245	6257	6245	6244	6244	6249	6243	6244	6243
6	6258	6258	6256	6258	6256	6253	6257	6244	6244	6246	6243	6244	6245	6248	6248
7	6258	6258	6258	6258	6256	6245	6256	6248	6244	6240	6246	6247	6247	6244	6253
8	6253	6253	6255	6253	6251	6250	6247	6239	6243	6244	6244	6242	6244	6247	6248
9	6256	6256	6258	6245	6256	6241	6243	6251	6240	6243	6244	6245	6246	6244	6244
10	6258	6258	6254	6256	6256	6257	6257	6252	6240	6244	6244	6240	6244	6244	6244
11	6244	6244	6255	6258	6244	6244	6243	6245	6244	6244	6244	6243	6244	6244	6244
12	6257	6257	6256	6258	6256	6244	6256	6257	6245	6244	6244	6247	6246	6244	6244
13	6257	6257	6256	6256	6256	6255	6256	6243	6243	6244	6243	6244	6245	6246	6250
14	6253	6253	6256	6242	6251	6253	6253	6240	6242	6240	6244	6247	6246	6246	6246
15	6258	6258	6258	6256	6255	6244	6257	6248	6243	6244	6244	6247	6244	6246	6246
16	6256	6256	6255	6257	6256	6256	6255	6257	6243	6244	6244	6246	6247	6247	6247
17	6258	6258	6256	6255	6256	6250	6256	6248	6240	6243	6244	6244	6244	6247	6247
18	6258	6258	6255	6260	6257	6254	6244	6248	6244	6244	6244	6244	6247	6244	6244
19	6254	6254	6256	6243	6255	6244	6244	6244	6245	6241	6244	6244	6247	6250	6244
20	6256	6256	6255	6258	6257	6255	6255	6256	6243	6243	6244	6244	6244	6244	6244
21	6257	6257	6256	6256	6256	6258	6257	6239	6244	6242	6243	6243	6244	6246	6244
22	6258	6258	6256	6253	6244	6244	6244	6240	6244	6244	6244	6244	6246	6244	6244
23	6258	6258	6256	6258	6257	6244	6255	6249	6244	6243	6244	6244	6244	6246	6247
25	6258	6258	6256	6258	6256	6244	6256	6255	6244	6243	6243	6247	6241	6244	6244
30	6257	6257	6255	6253	6258	6243	6258	6242	6245	6244	6244	6244	6246	6244	6244
40	6257	6257	6256	6259	6256	6256	6256	6257	6243	6244	6244	6244	6244	6246	6246

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	6242 bytes	–	100%
1,000	6240 bytes	-2 bytes	100%
10,000	6240 bytes	–	100%
100,000	6239 bytes	-1 byte	3.77%
1,000,000	6239 bytes	–	0.58%
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)	6252 bytes	+13 bytes (+0.21%)	–
1	6252 bytes	+13 bytes (+0.21%)	–
2	6272 bytes	+33 bytes (+0.53%)	+20 bytes
3	6274 bytes	+35 bytes (+0.56%)	+22 bytes
4	6302 bytes	+63 bytes (+1.01%)	+50 bytes
5	6336 bytes	+97 bytes (+1.55%)	+84 bytes
6	6368 bytes	+129 bytes (+2.07%)	+116 bytes
7	6405 bytes	+166 bytes (+2.66%)	+153 bytes
8	6439 bytes	+200 bytes (+3.21%)	+187 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	5490 bytes	-749 bytes (-12.01%)
Brotli (Wikipedia)	brotli	brotli -q 11	5843 bytes	-396 bytes (-6.35%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	5854 bytes	-385 bytes (-6.17%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	6131 bytes	-108 bytes (-1.73%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	6239 bytes	– (0.00%)
Zstandard (Wikipedia)	zstd	zstd -19	6269 bytes	+30 bytes (+0.48%)
LZMA2 (Wikipedia)	xz	xz -9	6284 bytes	+45 bytes (+0.72%)

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 2024.
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.