UnderscoreJS 1.10.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 60068 bytes (58.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 17547 bytes (17.1k, 29%).

After GZIP compression these minified files vary in size:

unpkg	7483 bytes (7.3k)	CDN
Boot	6745 bytes (6.6k)	CDN
cdnjs	6745 bytes (6.6k)	CDN
gzip -6 (default)	6741 bytes (6.6k)	local copy
gzip -9	6737 bytes (6.6k)	local copy
libdeflate -12	6572 bytes (6.4k)	local copy
7zip -mx=9 -tgzip	6570 bytes (6.4k)	local copy
kzip -s0 -rn -b0	6563 bytes (6.4k)	local copy
zultra	6563 bytes (6.4k)	local copy
pigz -11 -n	6559 bytes (6.4k)	local copy
Zopfli	6543 bytes (6.4k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.10.2 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 202 bytes by using my UnderscoreJS 1.10.2 Zopfli version instead of the best available CDN (3.09% smaller than cdnjs, 6543 vs. 6745 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 --i1000000 --mb8 --mls8192 --bsr9 --lazy --ohh

(found May 19, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	8192	--mls8192
block splitting recursion	9	--bsr9
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/1.10.2/underscore-min.js --location | md5sum
52caef864228e0b4ca9f97eced0ab2bb -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.2.min.zopfli.js.gz | md5sum
52caef864228e0b4ca9f97eced0ab2bb -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.10.2/underscore-min.js --location | sha1sum
e4cf51325358922e7ceb95707827ba7f19d7fc18 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.2.min.zopfli.js.gz | sha1sum
e4cf51325358922e7ceb95707827ba7f19d7fc18 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
unpkg	7483 bytes	52caef864228e0b4ca9f97eced0ab2bb	(invalid)
Boot	6745 bytes	52caef864228e0b4ca9f97eced0ab2bb	May 30, 2020 @ 05:16
cdnjs	6745 bytes	52caef864228e0b4ca9f97eced0ab2bb	May 30, 2020 @ 05:16

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
6543 bytes	-1 byte	zopfli --i1000000 --mls8192 --bsr9 --lazy --ohh	May 19, 2020 @ 19:01
6544 bytes	-2 bytes	zopfli --i10000 --mls2048 --bsr14 --lazy --ohh	May 19, 2020 @ 14:38
6546 bytes	-2 bytes	zopfli --i1000 --mls2048 --bsr14 --lazy --ohh	May 19, 2020 @ 14:36
6548 bytes	–	zopfli --i100 --mls2048 --bsr14 --lazy --ohh	May 19, 2020 @ 14:32

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 @ 12:48.

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:
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	6564	6564	6563	6565	6564	6554	6560	6559	6559	6562	6562	6562	6562	6562	6562
4	6561	6559	6560	6560	6558	6552	6551	6553	6553	6556	6556	6562	6548	6547	6547
6	6559	6564	6559	6559	6559	6559	6557	6554	6558	6556	6545	6545	6561	6552	6552
7	6559	6559	6560	6554	6558	6554	6564	6559	6560	6560	6557	6562	6546	6546	6546
8	6564	6564	6558	6559	6564	6565	6563	6558	6555	6558	6562	6552	6545	6546	6546
9	6557	6557	6556	6549	6562	6553	6551	6554	6558	6560	6546	6562	6543	6548	6548
10	6559	6560	6558	6559	6559	6559	6560	6559	6553	6549	6562	6562	6563	6546	6546
11	6563	6563	6559	6559	6559	6559	6564	6560	6559	6558	6552	6562	6546	6546	6546
12	6565	6564	6565	6563	6565	6554	6548	6557	6559	6558	6545	6562	6563	6547	6546
13	6556	6558	6558	6559	6558	6559	6563	6559	6558	6558	6545	6546	6546	6548	6548
14	6564	6564	6559	6552	6552	6556	6552	6554	6558	6551	6543	6546	6545	6547	6547
15	6559	6559	6556	6559	6556	6559	6565	6559	6558	6558	6556	6562	6550	6548	6548
16	6559	6558	6558	6552	6558	6556	6548	6559	6558	6558	6549	6548	6545	6548	6548
17	6564	6564	6558	6559	6559	6559	6548	6561	6559	6559	6546	6548	6545	6548	6547
18	6564	6565	6558	6559	6558	6556	6548	6554	6558	6550	6546	6546	6564	6546	6546
19	6555	6556	6558	6555	6559	6556	6556	6559	6559	6558	6545	6546	6545	6547	6547
20	6559	6564	6558	6558	6555	6557	6549	6558	6558	6558	6549	6546	6545	6552	6552
21	6564	6563	6559	6564	6559	6559	6560	6559	6558	6559	6562	6549	6546	6549	6549
22	6559	6564	6558	6558	6559	6556	6563	6559	6559	6556	6545	6546	6546	6547	6547
23	6563	6563	6558	6558	6558	6559	6558	6559	6558	6558	6545	6560	6546	6547	6547
25	6564	6564	6558	6559	6558	6559	6549	6558	6558	6558	6553	6562	6563	6550	6550
30	6559	6559	6559	6559	6559	6559	6552	6558	6558	6556	6545	6548	6562	6546	6546
40	6559	6564	6560	6559	6558	6559	6560	6560	6559	6558	6543	6544	6545	6545	6546

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	6548 bytes	–	100%
1,000	6546 bytes	-2 bytes	100%
10,000	6544 bytes	-2 bytes	100%
100,000	6544 bytes	–	2.03%
1,000,000	6543 bytes	-1 byte	1.16%
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)	6563 bytes	+20 bytes (+0.31%)	–
1	6563 bytes	+20 bytes (+0.31%)	–
2	6579 bytes	+36 bytes (+0.55%)	+16 bytes
3	6603 bytes	+60 bytes (+0.92%)	+40 bytes
4	6620 bytes	+77 bytes (+1.18%)	+57 bytes
5	6624 bytes	+81 bytes (+1.24%)	+61 bytes
6	6653 bytes	+110 bytes (+1.68%)	+90 bytes
7	6690 bytes	+147 bytes (+2.25%)	+127 bytes
8	6714 bytes	+171 bytes (+2.61%)	+151 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	5867 bytes	-676 bytes (-10.33%)
Brotli (Wikipedia)	brotli	brotli -q 11	6110 bytes	-433 bytes (-6.62%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	6120 bytes	-423 bytes (-6.46%)
Zstandard (Wikipedia)	zstd	zstd -19	6534 bytes	-9 bytes (-0.14%)
LZMA2 (Wikipedia)	xz	xz -9	6548 bytes	+5 bytes (+0.08%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	6557 bytes	+14 bytes (+0.21%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	6644 bytes	+101 bytes (+1.54%)

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.