UnderscoreJS 1.12.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 67455 bytes (65.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 19358 bytes (18.9k, 29%).

After GZIP compression these minified files vary in size:

unpkg	8216 bytes (8.0k)	CDN
Boot	7429 bytes (7.3k)	CDN
cdnjs	7429 bytes (7.3k)	CDN
gzip -6 (default)	7422 bytes (7.2k)	local copy
gzip -9	7413 bytes (7.2k)	local copy
libdeflate -12	7238 bytes (7.1k)	local copy
zultra	7231 bytes (7.1k)	local copy
kzip -s0 -rn -b1	7226 bytes (7.1k)	local copy
7zip -mx=9 -tgzip	7225 bytes (7.1k)	local copy
pigz -11 -n	7223 bytes (7.1k)	local copy
Zopfli	7207 bytes (7.0k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.12.0 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 222 bytes by using my UnderscoreJS 1.12.0 Zopfli version instead of the best available CDN (3.08% smaller than cdnjs, 7207 vs. 7429 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 --i10000 --mb8 --mls16384 --bsr8 --lazy --ohh

(found December 1, 2020)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	16384	--mls16384
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/1.12.0/underscore-min.js --location | md5sum
5e69b8b4c93891157f2dac3721873c59 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.0.min.zopfli.js.gz | md5sum
5e69b8b4c93891157f2dac3721873c59 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.12.0/underscore-min.js --location | sha1sum
ac0bc40622bb3babcb228f3662b67ed8ae1012a3 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.0.min.zopfli.js.gz | sha1sum
ac0bc40622bb3babcb228f3662b67ed8ae1012a3 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
unpkg	8216 bytes	5e69b8b4c93891157f2dac3721873c59	(invalid)
Boot	7429 bytes	5e69b8b4c93891157f2dac3721873c59	December 21, 2020 @ 10:19
cdnjs	7429 bytes	5e69b8b4c93891157f2dac3721873c59	December 21, 2020 @ 10:19

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
7207 bytes	-1 byte	zopfli --i10000 --mls16384 --bsr8 --lazy --ohh	December 1, 2020 @ 15:20
7208 bytes	-1 byte	zopfli --i10000 --mls256 --bsr20 --lazy --ohh	December 1, 2020 @ 15:06
7209 bytes	-3 bytes	zopfli --i1000 --mls8192 --bsr2 --lazy --ohh	December 1, 2020 @ 14:50
7212 bytes	–	zopfli --i100 --mls8192 --bsr19 --lazy --ohh	December 1, 2020 @ 14:30

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on December 21, 2020 @ 10:19.

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 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	7219	7219	7219	7219	7219	7210	7221	7210	7220	7216	7211	7210	7208	7207	7209
4	7216	7221	7216	7218	7217	7216	7216	7215	7219	7221	7208	7208	7208	7209	7209
6	7217	7215	7216	7216	7218	7216	7216	7216	7221	7214	7208	7216	7208	7209	7208
7	7217	7216	7216	7217	7217	7216	7216	7218	7219	7216	7215	7210	7208	7208	7208
8	7217	7216	7219	7216	7217	7210	7216	7210	7221	7216	7209	7212	7208	7207	7209
9	7217	7216	7216	7219	7217	7215	7216	7215	7220	7214	7216	7216	7209	7208	7209
10	7217	7216	7216	7217	7218	7217	7216	7209	7220	7215	7209	7209	7208	7209	7209
11	7216	7216	7216	7217	7217	7210	7216	7210	7217	7216	7214	7208	7213	7211	7208
12	7217	7216	7216	7217	7218	7216	7217	7216	7209	7216	7209	7209	7208	7208	7208
13	7218	7216	7216	7216	7217	7216	7216	7216	7221	7216	7216	7212	7209	7208	7208
14	7218	7216	7217	7217	7217	7208	7216	7209	7220	7216	7213	7208	7208	7209	7209
15	7217	7216	7216	7217	7218	7216	7217	7218	7221	7210	7216	7208	7208	7209	7209
16	7217	7216	7216	7217	7215	7217	7217	7210	7221	7216	7209	7209	7209	7210	7209
17	7216	7216	7216	7217	7218	7215	7217	7208	7221	7216	7216	7209	7209	7211	7209
18	7217	7216	7216	7217	7217	7216	7217	7218	7217	7216	7209	7211	7208	7208	7208
19	7217	7216	7216	7217	7217	7216	7217	7218	7216	7216	7209	7209	7208	7209	7209
20	7217	7217	7217	7217	7217	7208	7216	7208	7221	7216	7216	7210	7208	7209	7209
21	7218	7216	7216	7216	7217	7215	7217	7217	7216	7216	7209	7209	7209	7208	7208
22	7217	7217	7216	7217	7217	7217	7216	7216	7221	7216	7209	7208	7209	7209	7208
23	7217	7216	7216	7217	7217	7216	7217	7208	7212	7214	7212	7209	7209	7208	7208
25	7219	7216	7216	7217	7217	7216	7216	7217	7221	7209	7208	7209	7209	7208	7208
30	7218	7216	7216	7216	7217	7216	7216	7210	7215	7215	7209	7210	7209	7210	7210
40	7220	7216	7219	7216	7218	7216	7216	7215	7209	7215	7209	7210	7209	7208	7208

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	7212 bytes	–	100%
1,000	7209 bytes	-3 bytes	100%
10,000	7207 bytes	-2 bytes	100%
100,000	7207 bytes	–	0.58%
1,000,000	7207 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)	7226 bytes	+19 bytes (+0.26%)	–
1	7226 bytes	+19 bytes (+0.26%)	–
2	7226 bytes	+19 bytes (+0.26%)	–
3	7247 bytes	+40 bytes (+0.56%)	+21 bytes
4	7277 bytes	+70 bytes (+0.97%)	+51 bytes
5	7313 bytes	+106 bytes (+1.47%)	+87 bytes
6	7351 bytes	+144 bytes (+2.00%)	+125 bytes
7	7373 bytes	+166 bytes (+2.30%)	+147 bytes
8	7405 bytes	+198 bytes (+2.75%)	+179 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	6478 bytes	-729 bytes (-10.12%)
Brotli (Wikipedia)	brotli	brotli -q 11	6751 bytes	-456 bytes (-6.33%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	6868 bytes	-339 bytes (-4.70%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	7156 bytes	-51 bytes (-0.71%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	7199 bytes	-8 bytes (-0.11%)
LZMA2 (Wikipedia)	xz	xz -9	7200 bytes	-7 bytes (-0.10%)
Zstandard (Wikipedia)	zstd	zstd -19	7207 bytes	– (0.00%)

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.