UnderscoreJS 1.1.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 25181 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 8782 bytes (8.6k, 35%).

After GZIP compression these minified files vary in size:

Boot	3302 bytes (3.2k)	CDN
Baidu	3006 bytes (2.9k)	CDN
gzip -6 (default)	3005 bytes (2.9k)	local copy
gzip -9	2997 bytes (2.9k)	local copy
cdnjs	2990 bytes (2.9k)	CDN
unpkg	2985 bytes (2.9k)	CDN
libdeflate -12	2908 bytes (2.8k)	local copy
zultra	2908 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2907 bytes (2.8k)	local copy
kzip -s0 -rn -b0	2905 bytes (2.8k)	local copy
pigz -11 -n	2903 bytes (2.8k)	local copy
Zopfli	2902 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.1.0 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 83 bytes by using my UnderscoreJS 1.1.0 Zopfli version instead of the best available CDN (2.86% smaller than unpkg, 2902 vs. 2985 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 --mls256 --bsr14 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	1000	--i1000
maximum blocks	8	--mb8
maximum length score	256	--mls256
block splitting recursion	14	--bsr14
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/1.1.0/underscore-min.js --location | md5sum
560516f0dca540f35861d41ddfd377d7 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.0.min.zopfli.js.gz | md5sum
560516f0dca540f35861d41ddfd377d7 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.1.0/underscore-min.js --location | sha1sum
49a747d3284b1d04f3eb823a4188f7725004f823 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.0.min.zopfli.js.gz | sha1sum
49a747d3284b1d04f3eb823a4188f7725004f823 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3302 bytes	560516f0dca540f35861d41ddfd377d7	(invalid)
cdnjs	2990 bytes	560516f0dca540f35861d41ddfd377d7	(invalid)
unpkg	2985 bytes	560516f0dca540f35861d41ddfd377d7	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	3006 bytes	f98fc4acf252b197fcb0eccf17b84011	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
2902 bytes	-1 byte	zopfli --i1000 --mls256 --bsr14 --lazy --ohh	February 2, 2016 @ 19:07
2903 bytes	–	zopfli --i100 --mls16 --bsr19 --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 @ 12:48.

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	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
4	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
6	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
7	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
8	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
9	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
10	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
11	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
12	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
13	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
14	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
15	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
16	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
17	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
18	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
19	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
20	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
21	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
22	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
23	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
25	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
30	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902
40	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902	2902

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	2903 bytes	–	100%
1,000	2902 bytes	-1 byte	100%
10,000	2902 bytes	–	100%
100,000	2902 bytes	–	100%
1,000,000	2902 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)	2905 bytes	+3 bytes (+0.10%)	–
1	2905 bytes	+3 bytes (+0.10%)	–
2	2929 bytes	+27 bytes (+0.93%)	+24 bytes
3	2961 bytes	+59 bytes (+2.03%)	+56 bytes
4	2970 bytes	+68 bytes (+2.34%)	+65 bytes
5	3000 bytes	+98 bytes (+3.38%)	+95 bytes
6	3032 bytes	+130 bytes (+4.48%)	+127 bytes
7	3070 bytes	+168 bytes (+5.79%)	+165 bytes
8	3105 bytes	+203 bytes (+7.00%)	+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	2607 bytes	-295 bytes (-10.17%)
Brotli (Wikipedia)	brotli	brotli -q 11	2702 bytes	-200 bytes (-6.89%)
Zstandard (Wikipedia)	zstd	zstd -19	2908 bytes	+6 bytes (+0.21%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2919 bytes	+17 bytes (+0.59%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2956 bytes	+54 bytes (+1.86%)
LZMA2 (Wikipedia)	xz	xz -9	2988 bytes	+86 bytes (+2.96%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3479 bytes	+577 bytes (+19.88%)

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.