UnderscoreJS 1.1.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 25145 bytes (24.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 8686 bytes (8.5k, 35%).

After GZIP compression these minified files vary in size:

Boot	3196 bytes (3.1k)	CDN
gzip -6 (default)	2911 bytes (2.8k)	local copy
Baidu	2908 bytes (2.8k)	CDN
gzip -9	2907 bytes (2.8k)	local copy
unpkg	2907 bytes (2.8k)	CDN
cdnjs	2900 bytes (2.8k)	CDN
libdeflate -12	2822 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2821 bytes (2.8k)	local copy
zultra	2820 bytes (2.8k)	local copy
kzip -s0 -rn -b1	2819 bytes (2.8k)	local copy
pigz -11 -n	2816 bytes (2.8k)	local copy
Zopfli	2816 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.1.2 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 84 bytes by using my UnderscoreJS 1.1.2 Zopfli version instead of the best available CDN (2.98% smaller than cdnjs, 2816 vs. 2900 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 --i100 --mb8 --mls256 --bsr25 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	100	--i100
maximum blocks	8	--mb8
maximum length score	256	--mls256
block splitting recursion	25	--bsr25
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/1.1.2/underscore-min.js --location | md5sum
871e81f985fd52d6d1eb76c46e16cb24 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.2.min.zopfli.js.gz | md5sum
871e81f985fd52d6d1eb76c46e16cb24 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.1.2/underscore-min.js --location | sha1sum
bcdd63e18a8a7cf728253f738556ad3b88d74649 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.2.min.zopfli.js.gz | sha1sum
bcdd63e18a8a7cf728253f738556ad3b88d74649 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3196 bytes	871e81f985fd52d6d1eb76c46e16cb24	(invalid)
unpkg	2907 bytes	871e81f985fd52d6d1eb76c46e16cb24	July 11, 2016 @ 16:49
cdnjs	2900 bytes	871e81f985fd52d6d1eb76c46e16cb24	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2908 bytes	ea1c7faa3017f1d472843766865e58bc	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
2816 bytes	–	zopfli --i100 --mls256 --bsr25 --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 @ 12:49.

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	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
4	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
6	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
7	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
8	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
9	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
10	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
11	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
12	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
13	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
14	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
15	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
16	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
17	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
18	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
19	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
20	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
21	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
22	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
23	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
25	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
30	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816
40	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816	2816

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	2816 bytes	–	100%
1,000	2816 bytes	–	100%
10,000	2816 bytes	–	100%
100,000	2816 bytes	–	100%
1,000,000	2816 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)	2819 bytes	+3 bytes (+0.11%)	–
1	2819 bytes	+3 bytes (+0.11%)	–
2	2841 bytes	+25 bytes (+0.89%)	+22 bytes
3	2874 bytes	+58 bytes (+2.06%)	+55 bytes
4	2884 bytes	+68 bytes (+2.41%)	+65 bytes
5	2916 bytes	+100 bytes (+3.55%)	+97 bytes
6	2951 bytes	+135 bytes (+4.79%)	+132 bytes
7	2986 bytes	+170 bytes (+6.04%)	+167 bytes
8	3019 bytes	+203 bytes (+7.21%)	+200 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	2544 bytes	-272 bytes (-9.66%)
Brotli (Wikipedia)	brotli	brotli -q 11	2624 bytes	-192 bytes (-6.82%)
Zstandard (Wikipedia)	zstd	zstd -19	2833 bytes	+17 bytes (+0.60%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2844 bytes	+28 bytes (+0.99%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2875 bytes	+59 bytes (+2.10%)
LZMA2 (Wikipedia)	xz	xz -9	2920 bytes	+104 bytes (+3.69%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3427 bytes	+611 bytes (+21.70%)

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.