UnderscoreJS 1.4.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 40589 bytes (39.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 13430 bytes (13.1k, 33%).

After GZIP compression these minified files vary in size:

Boot	5154 bytes (5.0k)	CDN
gzip -6 (default)	4654 bytes (4.5k)	local copy
Baidu	4650 bytes (4.5k)	CDN
cdnjs	4648 bytes (4.5k)	CDN
gzip -9	4638 bytes (4.5k)	local copy
unpkg	4626 bytes (4.5k)	CDN
zultra	4520 bytes (4.4k)	local copy
7zip -mx=9 -tgzip	4517 bytes (4.4k)	local copy
libdeflate -12	4513 bytes (4.4k)	local copy
kzip -s0 -rn -b0	4509 bytes (4.4k)	local copy
pigz -11 -n	4504 bytes (4.4k)	local copy
Zopfli	4499 bytes (4.4k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.4.1 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 127 bytes by using my UnderscoreJS 1.4.1 Zopfli version instead of the best available CDN (2.82% smaller than unpkg, 4499 vs. 4626 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 --mls256 --bsr13 --lazy --ohh

(found September 20, 2015)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	256	--mls256
block splitting recursion	13	--bsr13
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/1.4.1/underscore-min.js --location | md5sum
a8167cbe4acedc5f0132f7b087c24bd0 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.1.min.zopfli.js.gz | md5sum
a8167cbe4acedc5f0132f7b087c24bd0 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.4.1/underscore-min.js --location | sha1sum
42394e7c9142b938e1d807c643d24107d7d9d317 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.1.min.zopfli.js.gz | sha1sum
42394e7c9142b938e1d807c643d24107d7d9d317 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	5154 bytes	a8167cbe4acedc5f0132f7b087c24bd0	(invalid)
cdnjs	4648 bytes	a8167cbe4acedc5f0132f7b087c24bd0	(invalid)
unpkg	4626 bytes	a8167cbe4acedc5f0132f7b087c24bd0	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4650 bytes	31e38eceaa491ef56199e268faab5e12	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
4499 bytes	-1 byte	zopfli --i10000 --mls256 --bsr13 --lazy --ohh	September 20, 2015 @ 16:48
4500 bytes	-1 byte	zopfli --i10000 --mls512 --bsr4 --lazy --ohh	September 8, 2015 @ 14:24
4501 bytes	–	zopfli --i100 --mls4096 --bsr6 --lazy --ohh	September 8, 2015 @ 10:33

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	4508	4508	4500	4501	4501	4500	4507	4501	4500	4500	4500	4501	4501	4502	4502
4	4507	4507	4507	4506	4506	4506	4507	4500	4500	4501	4509	4501	4503	4500	4500
6	4504	4504	4504	4504	4504	4502	4507	4500	4500	4500	4501	4500	4501	4500	4500
7	4504	4504	4505	4505	4504	4504	4505	4507	4500	4508	4501	4503	4501	4501	4501
8	4509	4509	4501	4500	4502	4502	4507	4499	4500	4501	4501	4502	4503	4500	4500
9	4505	4505	4505	4502	4502	4500	4504	4500	4500	4500	4500	4503	4501	4504	4504
10	4505	4505	4500	4500	4500	4500	4505	4500	4501	4500	4501	4502	4502	4501	4501
11	4505	4505	4500	4502	4503	4511	4505	4500	4500	4500	4501	4502	4501	4500	4500
12	4510	4510	4500	4502	4502	4502	4502	4500	4500	4500	4501	4504	4500	4501	4501
13	4507	4507	4500	4502	4502	4502	4503	4499	4500	4500	4501	4500	4501	4501	4501
14	4502	4502	4503	4500	4500	4501	4503	4500	4501	4503	4501	4504	4501	4500	4500
15	4504	4504	4502	4500	4500	4500	4504	4500	4500	4500	4501	4502	4500	4500	4500
16	4504	4504	4504	4500	4500	4511	4504	4500	4500	4500	4501	4507	4503	4502	4502
17	4504	4504	4500	4502	4502	4503	4500	4499	4500	4500	4505	4504	4503	4501	4501
18	4504	4504	4502	4502	4503	4502	4500	4500	4500	4504	4504	4502	4501	4501	4501
19	4505	4505	4504	4500	4502	4500	4500	4501	4500	4500	4501	4500	4501	4501	4501
20	4504	4504	4502	4503	4504	4500	4504	4500	4500	4500	4501	4502	4500	4501	4501
21	4505	4505	4502	4500	4500	4500	4500	4500	4500	4500	4501	4502	4502	4502	4502
22	4502	4502	4502	4502	4500	4502	4500	4500	4500	4500	4504	4500	4501	4502	4502
23	4502	4502	4502	4502	4503	4502	4504	4504	4502	4500	4504	4501	4500	4501	4501
25	4505	4505	4500	4500	4501	4500	4500	4500	4500	4501	4501	4500	4501	4501	4501
30	4504	4504	4502	4502	4501	4501	4501	4501	4500	4501	4503	4500	4502	4502	4502
40	4505	4505	4506	4500	4500	4500	4500	4500	4505	4500	4501	4500	4500	4500	4500

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	4501 bytes	–	100%
1,000	4500 bytes	-1 byte	100%
10,000	4499 bytes	-1 byte	100%
100,000	4499 bytes	–	0.87%
1,000,000	4499 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)	4509 bytes	+10 bytes (+0.22%)	–
1	4509 bytes	+10 bytes (+0.22%)	–
2	4527 bytes	+28 bytes (+0.62%)	+18 bytes
3	4529 bytes	+30 bytes (+0.67%)	+20 bytes
4	4561 bytes	+62 bytes (+1.38%)	+52 bytes
5	4597 bytes	+98 bytes (+2.18%)	+88 bytes
6	4633 bytes	+134 bytes (+2.98%)	+124 bytes
7	4660 bytes	+161 bytes (+3.58%)	+151 bytes
8	4691 bytes	+192 bytes (+4.27%)	+182 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	4015 bytes	-484 bytes (-10.76%)
Brotli (Wikipedia)	brotli	brotli -q 11	4180 bytes	-319 bytes (-7.09%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	4418 bytes	-81 bytes (-1.80%)
Zstandard (Wikipedia)	zstd	zstd -19	4521 bytes	+22 bytes (+0.49%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4536 bytes	+37 bytes (+0.82%)
LZMA2 (Wikipedia)	xz	xz -9	4588 bytes	+89 bytes (+1.98%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4864 bytes	+365 bytes (+8.11%)

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.