UnderscoreJS 1.1.7 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 29079 bytes (28.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 10260 bytes (10.0k, 35%).

After GZIP compression these minified files vary in size:

Boot	3922 bytes (3.8k)	CDN
Baidu	3545 bytes (3.5k)	CDN
gzip -6 (default)	3538 bytes (3.5k)	local copy
gzip -9	3537 bytes (3.5k)	local copy
unpkg	3533 bytes (3.5k)	CDN
cdnjs	3529 bytes (3.4k)	CDN
libdeflate -12	3445 bytes (3.4k)	local copy
7zip -mx=9 -tgzip	3443 bytes (3.4k)	local copy
zultra	3440 bytes (3.4k)	local copy
kzip -s0 -rn -b1	3439 bytes (3.4k)	local copy
pigz -11 -n	3433 bytes (3.4k)	local copy
Zopfli	3429 bytes (3.3k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.7.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.1.7 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 100 bytes by using my UnderscoreJS 1.1.7 Zopfli version instead of the best available CDN (2.92% smaller than cdnjs, 3429 vs. 3529 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 --mls4096 --bsr14 --lazy --ohh

(found February 12, 2019)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	4096	--mls4096
block splitting recursion	14	--bsr14
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/1.1.7/underscore-min.js --location | md5sum
6f6cfe9c37413b6951178ff862e06ffc -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.7.min.zopfli.js.gz | md5sum
6f6cfe9c37413b6951178ff862e06ffc -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.1.7/underscore-min.js --location | sha1sum
81afb4cd3755671fea5e74d7118d7d460c475308 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.7.min.zopfli.js.gz | sha1sum
81afb4cd3755671fea5e74d7118d7d460c475308 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3922 bytes	6f6cfe9c37413b6951178ff862e06ffc	(invalid)
unpkg	3533 bytes	6f6cfe9c37413b6951178ff862e06ffc	July 11, 2016 @ 16:49
cdnjs	3529 bytes	6f6cfe9c37413b6951178ff862e06ffc	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	3545 bytes	e1cb863a7854988cacf4371b5a4d02d9	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
3429 bytes	-1 byte	zopfli --i100000 --mls4096 --bsr14 --lazy --ohh	February 12, 2019 @ 17:28
3430 bytes	-1 byte	zopfli --i10000 --mls64 --bsr18 --lazy --ohh	February 2, 2016 @ 22:11
3431 bytes	-1 byte	zopfli --i1000 --mls1024 --bsr6 --lazy --ohh	February 2, 2016 @ 19:46
3432 bytes	–	zopfli --i100 --mls32 --bsr17 --lazy --ohh	February 2, 2016 @ 19:07

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 @ 12:55.

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	3433	3433	3432	3432	3432	3432	3432	3432	3432	3433	3433	3433	3431	3432	3432
4	3433	3433	3432	3432	3432	3432	3431	3432	3432	3433	3433	3433	3431	3431	3431
6	3432	3432	3433	3432	3431	3433	3432	3432	3431	3431	3431	3431	3430	3430	3430
7	3433	3433	3431	3431	3432	3430	3431	3432	3432	3431	3431	3432	3431	3431	3431
8	3432	3432	3432	3431	3432	3431	3431	3432	3430	3431	3431	3432	3431	3431	3431
9	3432	3432	3431	3430	3432	3430	3431	3432	3431	3431	3431	3433	3431	3431	3431
10	3432	3432	3431	3431	3432	3430	3431	3432	3431	3431	3431	3432	3431	3431	3431
11	3432	3432	3431	3432	3432	3433	3433	3432	3431	3432	3431	3429	3429	3430	3430
12	3432	3432	3431	3432	3432	3433	3432	3432	3432	3432	3431	3432	3430	3430	3430
13	3432	3432	3431	3432	3432	3432	3431	3432	3432	3431	3431	3431	3429	3430	3430
14	3432	3432	3431	3431	3431	3432	3432	3432	3431	3432	3432	3429	3431	3431	3431
15	3432	3432	3431	3431	3432	3433	3432	3432	3430	3431	3431	3431	3430	3430	3430
16	3432	3432	3431	3431	3432	3433	3431	3432	3430	3431	3431	3433	3429	3430	3430
17	3432	3432	3431	3432	3431	3433	3432	3431	3431	3431	3431	3431	3433	3430	3430
18	3432	3432	3433	3432	3432	3430	3432	3431	3431	3431	3431	3432	3431	3431	3431
19	3432	3432	3431	3431	3431	3433	3433	3432	3430	3431	3432	3431	3431	3431	3431
20	3432	3432	3431	3432	3432	3430	3432	3432	3431	3431	3431	3431	3431	3431	3431
21	3433	3433	3431	3431	3431	3433	3432	3432	3431	3431	3432	3432	3431	3431	3431
22	3433	3433	3431	3431	3431	3430	3431	3432	3432	3432	3431	3431	3431	3431	3431
23	3432	3432	3432	3431	3431	3430	3433	3431	3432	3431	3431	3430	3430	3430	3430
25	3432	3432	3432	3431	3431	3430	3432	3432	3432	3431	3431	3432	3433	3430	3430
30	3432	3432	3433	3431	3432	3432	3432	3431	3432	3432	3431	3432	3430	3430	3430
40	3432	3432	3431	3433	3432	3432	3432	3431	3432	3431	3431	3429	3431	3431	3431

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	3432 bytes	–	100%
1,000	3431 bytes	-1 byte	100%
10,000	3430 bytes	-1 byte	100%
100,000	3429 bytes	-1 byte	13.04%
1,000,000	3429 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)	3439 bytes	+10 bytes (+0.29%)	–
1	3439 bytes	+10 bytes (+0.29%)	–
2	3461 bytes	+32 bytes (+0.93%)	+22 bytes
3	3458 bytes	+29 bytes (+0.85%)	+19 bytes
4	3484 bytes	+55 bytes (+1.60%)	+45 bytes
5	3519 bytes	+90 bytes (+2.62%)	+80 bytes
6	3551 bytes	+122 bytes (+3.56%)	+112 bytes
7	3578 bytes	+149 bytes (+4.35%)	+139 bytes
8	3611 bytes	+182 bytes (+5.31%)	+172 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	3082 bytes	-347 bytes (-10.12%)
Brotli (Wikipedia)	brotli	brotli -q 11	3165 bytes	-264 bytes (-7.70%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3394 bytes	-35 bytes (-1.02%)
Zstandard (Wikipedia)	zstd	zstd -19	3456 bytes	+27 bytes (+0.79%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	3469 bytes	+40 bytes (+1.17%)
LZMA2 (Wikipedia)	xz	xz -9	3536 bytes	+107 bytes (+3.12%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3951 bytes	+522 bytes (+15.22%)

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

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