UnderscoreJS 1.0.4 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 24953 bytes (24.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 8690 bytes (8.5k, 35%).

After GZIP compression these minified files vary in size:

Boot	3275 bytes (3.2k)	CDN
gzip -6 (default)	2973 bytes (2.9k)	local copy
Baidu	2969 bytes (2.9k)	CDN
gzip -9	2967 bytes (2.9k)	local copy
cdnjs	2956 bytes (2.9k)	CDN
unpkg	2952 bytes (2.9k)	CDN
libdeflate -12	2875 bytes (2.8k)	local copy
zultra	2875 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2872 bytes (2.8k)	local copy
kzip -s0 -rn -b0	2872 bytes (2.8k)	local copy
pigz -11 -n	2870 bytes (2.8k)	local copy
Zopfli	2868 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.4.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.0.4 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 1.0.4 Zopfli version instead of the best available CDN (2.93% smaller than unpkg, 2868 vs. 2952 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 --mls256 --bsr25 --lazy --ohh

(found February 11, 2019)

Description	Value	Parameter
iterations	100000	--i100000
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/1.0.4/underscore-min.js --location | md5sum
cd539dbf84740fbaf28bb3e6750f646f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.4.min.zopfli.js.gz | md5sum
cd539dbf84740fbaf28bb3e6750f646f -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.0.4/underscore-min.js --location | sha1sum
ee68308411c690cd51cc8a43fe6ae60d3d1678af -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.4.min.zopfli.js.gz | sha1sum
ee68308411c690cd51cc8a43fe6ae60d3d1678af -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3275 bytes	cd539dbf84740fbaf28bb3e6750f646f	(invalid)
cdnjs	2956 bytes	cd539dbf84740fbaf28bb3e6750f646f	(invalid)
unpkg	2952 bytes	cd539dbf84740fbaf28bb3e6750f646f	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2969 bytes	e36a84958e3e3d8a03ddcbcf551189c3	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
2868 bytes	-1 byte	zopfli --i100000 --mls256 --bsr25 --lazy --ohh	February 11, 2019 @ 15:07
2869 bytes	–	zopfli --i100 --mls8 --bsr10 --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 @ 12:54.

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	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
4	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
6	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
7	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
8	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
9	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
10	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
11	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
12	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
13	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
14	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
15	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
16	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
17	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
18	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
19	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
20	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
21	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
22	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
23	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
25	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
30	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869
40	2868	2868	2869	2869	2869	2869	2868	2868	2868	2869	2868	2869	2869	2869	2869

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	2869 bytes	–	100%
1,000	2869 bytes	–	100%
10,000	2869 bytes	–	100%
100,000	2868 bytes	-1 byte	100%
1,000,000	2868 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)	2872 bytes	+4 bytes (+0.14%)	–
1	2872 bytes	+4 bytes (+0.14%)	–
2	2897 bytes	+29 bytes (+1.01%)	+25 bytes
3	2929 bytes	+61 bytes (+2.13%)	+57 bytes
4	2937 bytes	+69 bytes (+2.41%)	+65 bytes
5	2969 bytes	+101 bytes (+3.52%)	+97 bytes
6	3002 bytes	+134 bytes (+4.67%)	+130 bytes
7	3038 bytes	+170 bytes (+5.93%)	+166 bytes
8	3074 bytes	+206 bytes (+7.18%)	+202 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	2577 bytes	-291 bytes (-10.15%)
Brotli (Wikipedia)	brotli	brotli -q 11	2666 bytes	-202 bytes (-7.04%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2883 bytes	+15 bytes (+0.52%)
Zstandard (Wikipedia)	zstd	zstd -19	2883 bytes	+15 bytes (+0.52%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2912 bytes	+44 bytes (+1.53%)
LZMA2 (Wikipedia)	xz	xz -9	2960 bytes	+92 bytes (+3.21%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3456 bytes	+588 bytes (+20.50%)

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.