UnderscoreJS 1.1.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 25230 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 8758 bytes (8.6k, 35%).

After GZIP compression these minified files vary in size:

Boot	3247 bytes (3.2k)	CDN
Baidu	2945 bytes (2.9k)	CDN
gzip -6 (default)	2945 bytes (2.9k)	local copy
gzip -9	2939 bytes (2.9k)	local copy
unpkg	2935 bytes (2.9k)	CDN
cdnjs	2933 bytes (2.9k)	CDN
zultra	2858 bytes (2.8k)	local copy
libdeflate -12	2856 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2854 bytes (2.8k)	local copy
kzip -s0 -rn -b0	2853 bytes (2.8k)	local copy
pigz -11 -n	2851 bytes (2.8k)	local copy
Zopfli	2850 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.1.1 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 83 bytes by using my UnderscoreJS 1.1.1 Zopfli version instead of the best available CDN (2.91% smaller than cdnjs, 2850 vs. 2933 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 --i1000 --mb8 --mls512 --bsr13 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	1000	--i1000
maximum blocks	8	--mb8
maximum length score	512	--mls512
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/1.1.1/underscore-min.js --location | md5sum
f8b8f0bbdb1570777f5274c70eaf1414 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.1.min.zopfli.js.gz | md5sum
f8b8f0bbdb1570777f5274c70eaf1414 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.1.1/underscore-min.js --location | sha1sum
5de53da57fc8b7ab6c77d597c22875d747352fef -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.1.min.zopfli.js.gz | sha1sum
5de53da57fc8b7ab6c77d597c22875d747352fef -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3247 bytes	f8b8f0bbdb1570777f5274c70eaf1414	(invalid)
unpkg	2935 bytes	f8b8f0bbdb1570777f5274c70eaf1414	July 11, 2016 @ 16:49
cdnjs	2933 bytes	f8b8f0bbdb1570777f5274c70eaf1414	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2945 bytes	0a41b3c224b1c9a256d0a815402dd1ba	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
2850 bytes	-1 byte	zopfli --i1000 --mls512 --bsr13 --lazy --ohh	February 2, 2016 @ 19:50
2851 bytes	–	zopfli --i100 --mls16384 --bsr7 --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:
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	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
4	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
6	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
7	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
8	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
9	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
10	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
11	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
12	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
13	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
14	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
15	2860	2860	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
16	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
17	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
18	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
19	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
20	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
21	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
22	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
23	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
25	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
30	2859	2859	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850
40	2858	2858	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850	2850

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	2851 bytes	–	100%
1,000	2850 bytes	-1 byte	100%
10,000	2850 bytes	–	100%
100,000	2850 bytes	–	88.99%
1,000,000	2850 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)	2853 bytes	+3 bytes (+0.11%)	–
1	2853 bytes	+3 bytes (+0.11%)	–
2	2877 bytes	+27 bytes (+0.95%)	+24 bytes
3	2906 bytes	+56 bytes (+1.96%)	+53 bytes
4	2916 bytes	+66 bytes (+2.32%)	+63 bytes
5	2950 bytes	+100 bytes (+3.51%)	+97 bytes
6	2982 bytes	+132 bytes (+4.63%)	+129 bytes
7	3016 bytes	+166 bytes (+5.82%)	+163 bytes
8	3052 bytes	+202 bytes (+7.09%)	+199 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	2564 bytes	-286 bytes (-10.04%)
Brotli (Wikipedia)	brotli	brotli -q 11	2648 bytes	-202 bytes (-7.09%)
Zstandard (Wikipedia)	zstd	zstd -19	2859 bytes	+9 bytes (+0.32%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2867 bytes	+17 bytes (+0.60%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2910 bytes	+60 bytes (+2.11%)
LZMA2 (Wikipedia)	xz	xz -9	2944 bytes	+94 bytes (+3.30%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3445 bytes	+595 bytes (+20.88%)

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.