UnderscoreJS 1.4.4 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 41417 bytes (40.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 13450 bytes (13.1k, 32%).

After GZIP compression these minified files vary in size:

Boot	5133 bytes (5.0k)	CDN
jsdelivr	5133 bytes (5.0k)	CDN
gzip -6 (default)	4613 bytes (4.5k)	local copy
Baidu	4608 bytes (4.5k)	CDN
cdnjs	4608 bytes (4.5k)	CDN
gzip -9	4601 bytes (4.5k)	local copy
unpkg	4591 bytes (4.5k)	CDN
Sina	4589 bytes (4.5k)	CDN
zultra	4492 bytes (4.4k)	local copy
7zip -mx=9 -tgzip	4484 bytes (4.4k)	local copy
libdeflate -12	4481 bytes (4.4k)	local copy
pigz -11 -n	4480 bytes (4.4k)	local copy
kzip -s0 -rn -b0	4477 bytes (4.4k)	local copy
Zopfli	4477 bytes (4.4k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.4.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.4.4 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 112 bytes by using my UnderscoreJS 1.4.4 Zopfli version instead of the best available CDN (2.50% smaller than Sina, 4477 vs. 4589 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 --bsr4 --lazy --ohh

(found September 8, 2015)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	4096	--mls4096
block splitting recursion	4	--bsr4
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/1.4.4/underscore-min.js --location | md5sum
6dc59d3a72ad547168cf823c2fddc728 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.4.min.zopfli.js.gz | md5sum
6dc59d3a72ad547168cf823c2fddc728 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.4.4/underscore-min.js --location | sha1sum
048c69640ac8f0a3add4f2fd219a2fcb12a27d73 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.4.min.zopfli.js.gz | sha1sum
048c69640ac8f0a3add4f2fd219a2fcb12a27d73 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	5133 bytes	6dc59d3a72ad547168cf823c2fddc728	(invalid)
jsdelivr	5133 bytes	6dc59d3a72ad547168cf823c2fddc728	(invalid)
Baidu	4608 bytes	6dc59d3a72ad547168cf823c2fddc728	(invalid)
cdnjs	4608 bytes	6dc59d3a72ad547168cf823c2fddc728	(invalid)
unpkg	4591 bytes	6dc59d3a72ad547168cf823c2fddc728	July 11, 2016 @ 16:49
Sina	4589 bytes	6dc59d3a72ad547168cf823c2fddc728	(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
4477 bytes	-1 byte	zopfli --i10000 --mls4096 --bsr4 --lazy --ohh	September 8, 2015 @ 13:43
4478 bytes	-1 byte	zopfli --i1000 --mls512 --bsr2 --lazy --ohh	September 8, 2015 @ 10:47
4479 bytes	–	zopfli --i100 --mls4096 --bsr9 --lazy --ohh	September 8, 2015 @ 10:32

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 @ 12:43.

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	4477	4477	4484	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4483	4483
4	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4477	4477	4477
6	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4480	4481	4481
7	4477	4477	4482	4478	4478	4477	4477	4478	4478	4478	4479	4477	4480	4482	4482
8	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4482	4482
9	4483	4483	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4481	4481
10	4483	4483	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4481	4481
11	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4483	4483
12	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4483	4483
13	4477	4477	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4483	4483
14	4477	4477	4484	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4483	4483
15	4477	4477	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4480	4481	4481
16	4483	4483	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4481	4481
17	4482	4482	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4483	4483	4483
18	4483	4483	4484	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4482	4482
19	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4481	4481
20	4477	4477	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4482	4482	4482
21	4483	4483	4483	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4481	4481
22	4477	4477	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4482	4482	4482
23	4483	4483	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4482	4482	4482
25	4477	4477	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4480	4481	4481
30	4482	4482	4484	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4481	4481
40	4482	4482	4481	4478	4478	4477	4477	4478	4478	4478	4479	4477	4481	4482	4482

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	4479 bytes	–	100%
1,000	4478 bytes	-1 byte	100%
10,000	4477 bytes	-1 byte	100%
100,000	4477 bytes	–	28.99%
1,000,000	4477 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)	4477 bytes	– (0.00%)	–
1	4477 bytes	– (0.00%)	–
2	4499 bytes	+22 bytes (+0.49%)	+22 bytes
3	4527 bytes	+50 bytes (+1.12%)	+50 bytes
4	4542 bytes	+65 bytes (+1.45%)	+65 bytes
5	4576 bytes	+99 bytes (+2.21%)	+99 bytes
6	4613 bytes	+136 bytes (+3.04%)	+136 bytes
7	4644 bytes	+167 bytes (+3.73%)	+167 bytes
8	4675 bytes	+198 bytes (+4.42%)	+198 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	3970 bytes	-507 bytes (-11.32%)
Brotli (Wikipedia)	brotli	brotli -q 11	4171 bytes	-306 bytes (-6.83%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	4388 bytes	-89 bytes (-1.99%)
Zstandard (Wikipedia)	zstd	zstd -19	4494 bytes	+17 bytes (+0.38%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4500 bytes	+23 bytes (+0.51%)
LZMA2 (Wikipedia)	xz	xz -9	4560 bytes	+83 bytes (+1.85%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4824 bytes	+347 bytes (+7.75%)

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.