UnderscoreJS 1.4.3 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 41344 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 13432 bytes (13.1k, 32%).

After GZIP compression these minified files vary in size:

Boot	5142 bytes (5.0k)	CDN
jsdelivr	5142 bytes (5.0k)	CDN
gzip -6 (default)	4627 bytes (4.5k)	local copy
Baidu	4616 bytes (4.5k)	CDN
cdnjs	4616 bytes (4.5k)	CDN
gzip -9	4613 bytes (4.5k)	local copy
unpkg	4607 bytes (4.5k)	CDN
zultra	4495 bytes (4.4k)	local copy
7zip -mx=9 -tgzip	4490 bytes (4.4k)	local copy
libdeflate -12	4488 bytes (4.4k)	local copy
pigz -11 -n	4488 bytes (4.4k)	local copy
kzip -s0 -rn -b1	4484 bytes (4.4k)	local copy
Zopfli	4483 bytes (4.4k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.3.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.4.3 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 124 bytes by using my UnderscoreJS 1.4.3 Zopfli version instead of the best available CDN (2.77% smaller than unpkg, 4483 vs. 4607 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 --mls8192 --bsr11 --lazy --ohh

(found February 13, 2019)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	8192	--mls8192
block splitting recursion	11	--bsr11
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/1.4.3/underscore-min.js --location | md5sum
45635c8658599ecae698d0d45efc480d -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.3.min.zopfli.js.gz | md5sum
45635c8658599ecae698d0d45efc480d -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.4.3/underscore-min.js --location | sha1sum
8438e159195ef97e07bd1c7fe16c7ffdd308eb58 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.4.3.min.zopfli.js.gz | sha1sum
8438e159195ef97e07bd1c7fe16c7ffdd308eb58 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	5142 bytes	45635c8658599ecae698d0d45efc480d	(invalid)
jsdelivr	5142 bytes	45635c8658599ecae698d0d45efc480d	(invalid)
Baidu	4616 bytes	45635c8658599ecae698d0d45efc480d	(invalid)
cdnjs	4616 bytes	45635c8658599ecae698d0d45efc480d	(invalid)
unpkg	4607 bytes	45635c8658599ecae698d0d45efc480d	July 11, 2016 @ 16:49

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
4483 bytes	-1 byte	zopfli --i100000 --mls8192 --bsr11 --lazy --ohh	February 13, 2019 @ 03:51
4484 bytes	-1 byte	zopfli --i100000 --mls4096 --bsr11 --lazy --ohh	February 13, 2019 @ 02:35
4485 bytes	-1 byte	zopfli --i1000 --mls512 --bsr2 --lazy --ohh	September 8, 2015 @ 10:48
4486 bytes	–	zopfli --i100 --mls1024 --bsr11 --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 @ 12:53.

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	4484	4484	4485	4484	4484	4485	4485	4484	4485	4485	4485	4484	4484	4491	4491
4	4487	4487	4486	4484	4484	4485	4485	4484	4485	4485	4485	4484	4486	4487	4487
6	4487	4487	4486	4485	4484	4485	4485	4484	4485	4485	4485	4484	4484	4485	4485
7	4487	4487	4484	4484	4484	4485	4485	4484	4485	4485	4485	4484	4486	4490	4490
8	4487	4487	4487	4483	4484	4485	4485	4484	4485	4485	4485	4484	4490	4490	4490
9	4487	4487	4486	4486	4484	4485	4485	4484	4485	4485	4485	4484	4486	4483	4483
10	4494	4494	4489	4486	4484	4485	4485	4484	4485	4485	4485	4484	4486	4488	4488
11	4487	4487	4486	4484	4484	4485	4485	4484	4485	4485	4485	4484	4483	4483	4483
12	4495	4495	4489	4485	4484	4485	4485	4484	4485	4485	4485	4484	4483	4486	4486
13	4494	4494	4489	4485	4484	4485	4485	4484	4485	4485	4485	4484	4486	4488	4488
14	4495	4495	4486	4485	4484	4485	4485	4484	4485	4485	4485	4484	4486	4486	4486
15	4487	4487	4484	4486	4484	4485	4485	4484	4485	4485	4485	4484	4486	4488	4488
16	4486	4486	4488	4486	4484	4485	4485	4484	4485	4485	4485	4484	4486	4485	4485
17	4487	4487	4486	4484	4484	4485	4485	4484	4485	4485	4485	4484	4484	4485	4485
18	4486	4486	4489	4484	4484	4485	4485	4484	4485	4485	4485	4484	4486	4483	4483
19	4487	4487	4486	4484	4484	4485	4485	4484	4485	4485	4485	4484	4484	4483	4483
20	4487	4487	4484	4485	4484	4485	4485	4484	4485	4485	4485	4484	4483	4483	4483
21	4494	4494	4494	4485	4484	4485	4485	4484	4485	4485	4485	4484	4483	4483	4483
22	4487	4487	4486	4485	4484	4485	4485	4484	4485	4485	4485	4484	4483	4485	4485
23	4486	4486	4486	4485	4484	4485	4485	4484	4485	4485	4485	4484	4483	4486	4486
25	4487	4487	4485	4486	4484	4485	4485	4484	4485	4485	4485	4484	4487	4486	4486
30	4487	4487	4487	4485	4484	4485	4485	4484	4485	4485	4485	4484	4484	4486	4486
40	4487	4487	4486	4485	4484	4485	4485	4484	4485	4485	4485	4484	4483	4483	4483

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	4486 bytes	–	100%
1,000	4485 bytes	-1 byte	100%
10,000	4485 bytes	–	100%
100,000	4483 bytes	-2 bytes	70.43%
1,000,000	4483 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)	4484 bytes	+1 byte (+0.02%)	–
1	4484 bytes	+1 byte (+0.02%)	–
2	4506 bytes	+23 bytes (+0.51%)	+22 bytes
3	4532 bytes	+49 bytes (+1.09%)	+48 bytes
4	4546 bytes	+63 bytes (+1.41%)	+62 bytes
5	4577 bytes	+94 bytes (+2.10%)	+93 bytes
6	4609 bytes	+126 bytes (+2.81%)	+125 bytes
7	4645 bytes	+162 bytes (+3.61%)	+161 bytes
8	4675 bytes	+192 bytes (+4.28%)	+191 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	3969 bytes	-514 bytes (-11.47%)
Brotli (Wikipedia)	brotli	brotli -q 11	4180 bytes	-303 bytes (-6.76%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	4384 bytes	-99 bytes (-2.21%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4499 bytes	+16 bytes (+0.36%)
Zstandard (Wikipedia)	zstd	zstd -19	4499 bytes	+16 bytes (+0.36%)
LZMA2 (Wikipedia)	xz	xz -9	4572 bytes	+89 bytes (+1.99%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4823 bytes	+340 bytes (+7.58%)

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.