UnderscoreJS 1.4.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 40966 bytes (40.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 13582 bytes (13.3k, 33%).

After GZIP compression these minified files vary in size:

jsdelivr	5193 bytes (5.1k)	CDN
Boot	5190 bytes (5.1k)	CDN
gzip -6 (default)	4677 bytes (4.6k)	local copy
Baidu	4671 bytes (4.6k)	CDN
cdnjs	4669 bytes (4.6k)	CDN
gzip -9	4659 bytes (4.5k)	local copy
unpkg	4650 bytes (4.5k)	CDN
7zip -mx=9 -tgzip	4541 bytes (4.4k)	local copy
zultra	4541 bytes (4.4k)	local copy
libdeflate -12	4536 bytes (4.4k)	local copy
kzip -s0 -rn -b1	4531 bytes (4.4k)	local copy
pigz -11 -n	4527 bytes (4.4k)	local copy
Zopfli	4521 bytes (4.4k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.4.2 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 129 bytes by using my UnderscoreJS 1.4.2 Zopfli version instead of the best available CDN (2.85% smaller than unpkg, 4521 vs. 4650 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 --mls1024 --bsr14 --lazy --ohh

(found November 23, 2015)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
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/1.4.2/underscore-min.js --location | md5sum
969feaaba18c01015451501674545f1f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.2.min.zopfli.js.gz | md5sum
969feaaba18c01015451501674545f1f -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.4.2/underscore-min.js --location | sha1sum
507452bd3e2df95b8945a1e5b251595c11e113b0 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.2.min.zopfli.js.gz | sha1sum
507452bd3e2df95b8945a1e5b251595c11e113b0 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	5190 bytes	969feaaba18c01015451501674545f1f	(invalid)
cdnjs	4669 bytes	969feaaba18c01015451501674545f1f	(invalid)
unpkg	4650 bytes	969feaaba18c01015451501674545f1f	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
jsdelivr	5193 bytes	90531ffe720f6b9306ac02aaf9606a00	only whitespaces differ	(invalid)
Baidu	4671 bytes	90531ffe720f6b9306ac02aaf9606a00	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
4521 bytes	-1 byte	zopfli --i100000 --mls1024 --bsr14 --lazy --ohh	November 23, 2015 @ 18:28
4522 bytes	-1 byte	zopfli --i10000 --mls1024 --bsr14 --lazy --ohh	September 8, 2015 @ 14:09
4523 bytes	-2 bytes	zopfli --i1000 --mls1024 --bsr14 --lazy --ohh	September 8, 2015 @ 10:50
4525 bytes	–	zopfli --i100 --mls4096 --bsr16 --lazy --ohh	September 8, 2015 @ 10:32

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 @ 12:48.

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	4532	4532	4535	4535	4525	4535	4532	4532	4525	4524	4525	4525	4524	4524	4524
4	4530	4530	4530	4529	4526	4527	4527	4528	4524	4524	4524	4525	4524	4524	4524
6	4528	4528	4525	4526	4527	4525	4524	4532	4525	4525	4524	4524	4524	4524	4524
7	4526	4526	4526	4526	4526	4526	4526	4526	4524	4529	4523	4524	4525	4525	4525
8	4529	4529	4530	4526	4527	4526	4528	4529	4524	4528	4525	4524	4525	4524	4524
9	4526	4526	4526	4527	4526	4523	4526	4528	4524	4525	4526	4525	4525	4525	4525
10	4527	4527	4526	4526	4536	4530	4527	4524	4525	4524	4523	4525	4527	4526	4526
11	4528	4528	4532	4536	4526	4527	4527	4529	4524	4525	4523	4524	4524	4525	4525
12	4525	4525	4526	4536	4536	4526	4527	4525	4524	4524	4524	4524	4525	4525	4525
13	4526	4526	4524	4526	4527	4526	4524	4529	4524	4524	4523	4525	4525	4525	4525
14	4528	4528	4525	4526	4524	4524	4527	4524	4524	4521	4526	4524	4524	4524	4524
15	4526	4526	4525	4526	4536	4526	4527	4529	4524	4526	4524	4525	4525	4524	4524
16	4526	4526	4526	4525	4526	4537	4525	4525	4526	4524	4526	4524	4525	4524	4524
17	4526	4526	4528	4527	4527	4526	4527	4529	4524	4525	4523	4524	4525	4525	4525
18	4525	4525	4526	4527	4527	4535	4524	4524	4526	4526	4525	4525	4525	4524	4524
19	4526	4526	4527	4525	4526	4523	4527	4530	4524	4525	4525	4523	4524	4524	4524
20	4526	4526	4526	4525	4527	4524	4526	4529	4525	4525	4523	4525	4524	4524	4524
21	4526	4526	4526	4527	4526	4526	4527	4529	4524	4525	4523	4525	4525	4528	4528
22	4525	4525	4525	4527	4526	4529	4527	4525	4524	4525	4523	4525	4525	4525	4525
23	4525	4525	4525	4526	4527	4526	4525	4529	4524	4524	4523	4525	4525	4524	4524
25	4528	4528	4528	4525	4537	4524	4529	4526	4523	4524	4524	4525	4525	4526	4526
30	4526	4526	4526	4535	4524	4524	4532	4527	4524	4523	4524	4524	4525	4524	4524
40	4526	4526	4526	4526	4526	4537	4527	4524	4524	4526	4524	4524	4525	4525	4525

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	4524 bytes	–	100%
1,000	4523 bytes	-1 byte	100%
10,000	4522 bytes	-1 byte	100%
100,000	4521 bytes	-1 byte	0.29%
1,000,000	4521 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)	4531 bytes	+10 bytes (+0.22%)	–
1	4531 bytes	+10 bytes (+0.22%)	–
2	4549 bytes	+28 bytes (+0.62%)	+18 bytes
3	4548 bytes	+27 bytes (+0.60%)	+17 bytes
4	4582 bytes	+61 bytes (+1.35%)	+51 bytes
5	4616 bytes	+95 bytes (+2.10%)	+85 bytes
6	4653 bytes	+132 bytes (+2.92%)	+122 bytes
7	4680 bytes	+159 bytes (+3.52%)	+149 bytes
8	4713 bytes	+192 bytes (+4.25%)	+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	4035 bytes	-486 bytes (-10.75%)
Brotli (Wikipedia)	brotli	brotli -q 11	4196 bytes	-325 bytes (-7.19%)
Zstandard (Wikipedia)	zstd	zstd -19	4541 bytes	+20 bytes (+0.44%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	4557 bytes	+36 bytes (+0.80%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4568 bytes	+47 bytes (+1.04%)
LZMA2 (Wikipedia)	xz	xz -9	4608 bytes	+87 bytes (+1.92%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4888 bytes	+367 bytes (+8.12%)

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.