UnderscoreJS 1.9.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 58233 bytes (56.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 18042 bytes (17.6k, 31%).

After GZIP compression these minified files vary in size:

Boot	7236 bytes (7.1k)	CDN
gzip -6 (default)	6450 bytes (6.3k)	local copy
gzip -9	6442 bytes (6.3k)	local copy
cdnjs	6418 bytes (6.3k)	CDN
unpkg	6418 bytes (6.3k)	CDN
7zip -mx=9 -tgzip	6252 bytes (6.1k)	local copy
zultra	6248 bytes (6.1k)	local copy
libdeflate -12	6245 bytes (6.1k)	local copy
pigz -11 -n	6243 bytes (6.1k)	local copy
kzip -s0 -rn -b1	6241 bytes (6.1k)	local copy
Zopfli	6231 bytes (6.1k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.9.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.9.0 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 187 bytes by using my UnderscoreJS 1.9.0 Zopfli version instead of the best available CDN (3.00% smaller than unpkg, 6231 vs. 6418 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 --i10000 --mb8 --mls4096 --bsr18 --lazy --ohh

(found April 23, 2018)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	4096	--mls4096
block splitting recursion	18	--bsr18
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/1.9.0/underscore-min.js --location | md5sum
8926a01daa0f08e58e7f19f5e7049a2d -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.9.0.min.zopfli.js.gz | md5sum
8926a01daa0f08e58e7f19f5e7049a2d -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.9.0/underscore-min.js --location | sha1sum
43ff9826cd320a8b680f364c7a8adf3da81cf571 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.9.0.min.zopfli.js.gz | sha1sum
43ff9826cd320a8b680f364c7a8adf3da81cf571 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	7236 bytes	8926a01daa0f08e58e7f19f5e7049a2d	(invalid)
cdnjs	6418 bytes	8926a01daa0f08e58e7f19f5e7049a2d	(invalid)
unpkg	6418 bytes	8926a01daa0f08e58e7f19f5e7049a2d	(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
6231 bytes	-1 byte	zopfli --i10000 --mls4096 --bsr18 --lazy --ohh	April 23, 2018 @ 10:45
6232 bytes	-1 byte	zopfli --i10000 --mls256 --bsr20 --lazy --ohh	April 23, 2018 @ 10:29
6233 bytes	–	zopfli --i100 --mls512 --bsr14 --lazy --ohh	April 23, 2018 @ 09:12

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 @ 12:51.

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	6239	6239	6247	6240	6246	6241	6241	6241	6241	6241	6241	6236	6239	6239	6239
4	6247	6247	6245	6247	6247	6246	6246	6241	6233	6232	6241	6237	6236	6236	6238
6	6248	6248	6246	6247	6247	6243	6249	6235	6238	6239	6235	6234	6235	6236	6236
7	6247	6247	6246	6247	6249	6243	6246	6233	6235	6236	6234	6234	6234	6236	6236
8	6240	6240	6243	6240	6247	6243	6246	6234	6233	6233	6234	6235	6236	6236	6236
9	6245	6245	6246	6246	6247	6245	6246	6241	6233	6235	6241	6231	6237	6238	6236
10	6246	6246	6247	6247	6247	6243	6246	6232	6233	6235	6242	6235	6237	6235	6235
11	6239	6239	6247	6247	6246	6236	6235	6235	6235	6234	6235	6234	6236	6238	6239
12	6246	6246	6247	6247	6247	6246	6246	6233	6235	6234	6241	6236	6236	6236	6240
13	6244	6244	6247	6247	6246	6249	6247	6232	6235	6235	6234	6234	6236	6236	6236
14	6247	6247	6247	6246	6233	6243	6233	6233	6232	6231	6234	6234	6233	6236	6236
15	6247	6247	6247	6247	6247	6243	6246	6234	6235	6235	6234	6234	6233	6236	6236
16	6244	6244	6246	6246	6249	6245	6246	6233	6232	6236	6231	6234	6236	6237	6236
17	6247	6247	6247	6247	6247	6247	6246	6234	6235	6235	6234	6234	6237	6238	6239
18	6246	6246	6247	6247	6247	6243	6246	6246	6232	6234	6241	6231	6236	6238	6236
19	6246	6246	6247	6245	6246	6235	6234	6235	6236	6232	6241	6236	6234	6236	6236
20	6246	6246	6247	6247	6247	6247	6246	6232	6235	6239	6234	6234	6235	6238	6239
21	6246	6246	6247	6247	6247	6243	6247	6234	6233	6235	6241	6235	6234	6236	6236
22	6245	6245	6247	6248	6247	6243	6246	6232	6233	6239	6234	6235	6233	6238	6239
23	6243	6243	6247	6247	6247	6244	6247	6247	6238	6239	6235	6236	6237	6236	6236
25	6246	6246	6247	6247	6247	6247	6246	6235	6235	6235	6234	6235	6231	6236	6236
30	6247	6247	6246	6247	6248	6244	6246	6234	6231	6234	6242	6234	6235	6236	6236
40	6246	6246	6246	6247	6246	6243	6246	6233	6233	6239	6241	6234	6236	6239	6236

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	6233 bytes	–	100%
1,000	6233 bytes	–	100%
10,000	6231 bytes	-2 bytes	100%
100,000	6231 bytes	–	4.35%
1,000,000	6231 bytes	–	1.74%
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)	6242 bytes	+11 bytes (+0.18%)	+1 byte
1	6241 bytes	+10 bytes (+0.16%)	–
2	6264 bytes	+33 bytes (+0.53%)	+23 bytes
3	6265 bytes	+34 bytes (+0.55%)	+24 bytes
4	6291 bytes	+60 bytes (+0.96%)	+50 bytes
5	6325 bytes	+94 bytes (+1.51%)	+84 bytes
6	6360 bytes	+129 bytes (+2.07%)	+119 bytes
7	6396 bytes	+165 bytes (+2.65%)	+155 bytes
8	6435 bytes	+204 bytes (+3.27%)	+194 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	5480 bytes	-751 bytes (-12.05%)
Brotli (Wikipedia)	brotli	brotli -q 11	5825 bytes	-406 bytes (-6.52%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	5845 bytes	-386 bytes (-6.19%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	6113 bytes	-118 bytes (-1.89%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	6236 bytes	+5 bytes (+0.08%)
Zstandard (Wikipedia)	zstd	zstd -19	6262 bytes	+31 bytes (+0.50%)
LZMA2 (Wikipedia)	xz	xz -9	6272 bytes	+41 bytes (+0.66%)

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.