UnderscoreJS 0.4.6 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 19960 bytes (19.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 7398 bytes (7.2k, 37%).

After GZIP compression these minified files vary in size:

Boot	2623 bytes (2.6k)	CDN
gzip -6 (default)	2395 bytes (2.3k)	local copy
gzip -9	2392 bytes (2.3k)	local copy
Baidu	2387 bytes (2.3k)	CDN
cdnjs	2375 bytes (2.3k)	CDN
7zip -mx=9 -tgzip	2326 bytes (2.3k)	local copy
libdeflate -12	2325 bytes (2.3k)	local copy
kzip -s0 -rn -b1	2322 bytes (2.3k)	local copy
pigz -11 -n	2320 bytes (2.3k)	local copy
zultra	2319 bytes (2.3k)	local copy
Zopfli	2317 bytes (2.3k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.6.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.4.6 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 58 bytes by using my UnderscoreJS 0.4.6 Zopfli version instead of the best available CDN (2.50% smaller than cdnjs, 2317 vs. 2375 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 --i1000000 --mb8 --mls16 --bsr7 --lazy --ohh

(found March 3, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	16	--mls16
block splitting recursion	7	--bsr7
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/0.4.6/underscore-min.js --location | md5sum
907b5b4566060b65cda7272b8b65a7f0 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.6.min.zopfli.js.gz | md5sum
907b5b4566060b65cda7272b8b65a7f0 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.4.6/underscore-min.js --location | sha1sum
c254351eda9212b2ae9a999972643d0419a4e408 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.6.min.zopfli.js.gz | sha1sum
c254351eda9212b2ae9a999972643d0419a4e408 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2623 bytes	907b5b4566060b65cda7272b8b65a7f0	(invalid)
cdnjs	2375 bytes	907b5b4566060b65cda7272b8b65a7f0	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2387 bytes	b9a925b5865fa994e871394287f0e4f7	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
2317 bytes	-1 byte	zopfli --i1000000 --mls16 --bsr7 --lazy --ohh	March 3, 2020 @ 18:29
2318 bytes	-1 byte	zopfli --i1000 --mls16 --bsr7 --lazy --ohh	February 2, 2016 @ 20:58
2319 bytes	–	zopfli --i100 --mls32768 --bsr25 --lazy --ohh	February 2, 2016 @ 20:57

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 @ 12:49.

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:
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	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
4	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
6	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
7	2318	2318	2318	2317	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
8	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
9	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
10	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
11	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
12	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
13	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
14	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
15	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
16	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
17	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
18	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
19	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
20	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
21	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
22	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
23	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
25	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
30	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318
40	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318	2318

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	2319 bytes	–	100%
1,000	2318 bytes	-1 byte	100%
10,000	2318 bytes	–	100%
100,000	2318 bytes	–	100%
1,000,000	2317 bytes	-1 byte	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)	2323 bytes	+6 bytes (+0.26%)	+1 byte
1	2322 bytes	+5 bytes (+0.22%)	–
2	2348 bytes	+31 bytes (+1.34%)	+26 bytes
3	2367 bytes	+50 bytes (+2.16%)	+45 bytes
4	2393 bytes	+76 bytes (+3.28%)	+71 bytes
5	2427 bytes	+110 bytes (+4.75%)	+105 bytes
6	2465 bytes	+148 bytes (+6.39%)	+143 bytes
7	2486 bytes	+169 bytes (+7.29%)	+164 bytes
8	2519 bytes	+202 bytes (+8.72%)	+197 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	2091 bytes	-226 bytes (-9.75%)
Brotli (Wikipedia)	brotli	brotli -q 11	2129 bytes	-188 bytes (-8.11%)
Zstandard (Wikipedia)	zstd	zstd -19	2337 bytes	+20 bytes (+0.86%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2393 bytes	+76 bytes (+3.28%)
LZMA2 (Wikipedia)	xz	xz -9	2416 bytes	+99 bytes (+4.27%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2551 bytes	+234 bytes (+10.10%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3005 bytes	+688 bytes (+29.69%)

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.