Choose a version:
22% The original file has 219913 bytes (214.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 47302 bytes (46.2k, 22%).

After GZIP compression these minified files vary in size:
Microsoft
  21861 bytes (21.3k)
CDN, direct link
Boot
  20002 bytes (19.5k)
CDN, direct link
unpkg
  19397 bytes (18.9k)
CDN, direct link
cdnjs
  17633 bytes (17.2k)
CDN, direct link
gzip -6 (default)
  17520 bytes (17.1k)
local copy
cdnhttps
  17498 bytes (17.1k)
CDN, direct link
gzip -9
  17476 bytes (17.1k)
local copy
jsdelivr
  17465 bytes (17.1k)
CDN, direct link
7zip -mx=9 -tgzip
  16969 bytes (16.6k)
local copy
libdeflate -12
  16965 bytes (16.6k)
local copy
kzip -s0 -rn -b2
  16943 bytes (16.5k)
local copy
pigz -11 -n
  16937 bytes (16.5k)
local copy
Zopfli
  16918 bytes (16.5k)
local copy
Zopfli (defluff)
  16917 bytes (16.5k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/knockout/knockout-3.1.0.min.js

You will automatically get the smallest Knockout 3.1.0 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 547 bytes by using my Knockout 3.1.0 Zopfli version instead of the best available CDN (3.23% smaller than jsdelivr, 16918 vs. 17465 bytes):
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 --mls512 --bsr15 --lazy --ohh

(found December 18, 2015)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 512  --mls512
block splitting recursion 15  --bsr15
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

Even Smaller Files Thanks To Defluff

Zopfli's output can be further optimized by the defluff tool.
In this particular case, defluff saves 1 more byte (16917 bytes).

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed http://knockoutjs.com/downloads/knockout-3.1.0.js --location | md5sum
8886eb570672900492aa46986160f8d2  -
curl --silent --compressed http://minime.stephan-brumme.com/files/knockout/knockout-3.1.0.min.zopfli.js.gz | md5sum
8886eb570672900492aa46986160f8d2  -

SHA1:
curl --silent --compressed http://knockoutjs.com/downloads/knockout-3.1.0.js --location | sha1sum
c52caf65b85eef4f291663e33ae289e12ff04fbd  -
curl --silent --compressed http://minime.stephan-brumme.com/files/knockout/knockout-3.1.0.min.zopfli.js.gz | sha1sum
c52caf65b85eef4f291663e33ae289e12ff04fbd  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Microsoft 21861 bytes 8886eb570672900492aa46986160f8d2 (invalid)
Boot 20002 bytes 8886eb570672900492aa46986160f8d2 (invalid)
unpkg 19397 bytes 8886eb570672900492aa46986160f8d2 July 11, 2016 @ 16:43
cdnjs 17633 bytes 8886eb570672900492aa46986160f8d2 (invalid)
cdnhttps 17498 bytes 8886eb570672900492aa46986160f8d2 December 24, 2015 @ 07:33
jsdelivr 17465 bytes 8886eb570672900492aa46986160f8d2 (invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available Knockout versions at minime.stephan-brumme.com:

3.4.2, 3.4.1, 3.4.0,
3.3.0,
3.2.0,
3.1.0,
3.0.0,
2.3.0,
2.2.1, 2.2.0,
2.1.0,
2.0.0,
1.2.1, 1.2.0,
1.1.2, 1.1.1, 1.1.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, jQuery, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
16918 bytes -2 bytes zopfli --i100000 --mls512 --bsr15 --lazy --ohh December 18, 2015 @ 07:17
16920 bytes -2 bytes zopfli --i10000 --mls512 --bsr12 --lazy --ohh September 10, 2015 @ 12:39
16922 bytes -1 byte zopfli --i1000 --mls512 --bsr13 --lazy --ohh September 10, 2015 @ 11:46
16923 bytes zopfli --i100 --mls512 --bsr10 --lazy --ohh September 10, 2015 @ 11:34

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on July 11, 2016 @ 16:43.

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 or 100,000.
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
16937 16925 16925 16925 16926 16936 16926 16924 16923 16923 16923 16931 16930 16935 16933
16927 16926 16925 16925 16926 16926 16927 16923 16924 16928 16922 16929 16928 16932 16940
16936 16924 16929 16927 16926 16928 16925 16927 16924 16927 16922 16930 16922 16932 16926
16933 16924 16927 16927 16928 16934 16922 16923 16925 16927 16922 16926 16928 16933 16930
16923 16923 16926 16927 16926 16933 16927 16923 16925 16928 16922 16927 16930 16933 16932
16929 16923 16926 16927 16934 16934 16927 16923 16919 16927 16923 16927 16928 16935 16927
16929 16927 16926 16927 16922 16922 16922 16924 16918 16922 16922 16927 16928 16932 16933
16923 16927 16922 16927 16925 16934 16927 16923 16919 16928 16920 16930 16927 16932 16937
16934 16924 16928 16927 16926 16927 16926 16926 16919 16928 16923 16928 16922 16932 16928
16923 16927 16924 16934 16922 16934 16934 16923 16918 16928 16924 16927 16926 16932 16935
16923 16927 16928 16924 16922 16926 16934 16924 16924 16928 16920 16927 16927 16933 16937
16934 16928 16922 16933 16933 16934 16927 16923 16918 16927 16923 16927 16928 16932 16928
16929 16927 16928 16927 16927 16927 16922 16923 16924 16926 16922 16926 16927 16933 16927
16928 16927 16924 16925 16923 16934 16926 16923 16919 16926 16919 16930 16928 16933 16933
16935 16928 16928 16927 16923 16927 16926 16923 16924 16926 16924 16927 16928 16933 16929
16928 16927 16933 16927 16927 16934 16924 16923 16919 16926 16920 16927 16928 16932 16929
16927 16927 16926 16922 16926 16926 16922 16924 16923 16926 16923 16930 16928 16933 16932
16929 16923 16926 16927 16922 16933 16927 16922 16918 16928 16922 16928 16928 16934 16933
16929 16927 16925 16927 16928 16923 16923 16923 16919 16926 16922 16922 16919 16925 16925
16927 16929 16926 16927 16925 16936 16927 16924 16919 16928 16919 16928 16928 16934 16938
16936 16927 16926 16922 16928 16934 16927 16924 16919 16927 16922 16928 16928 16932 16934
16923 16928 16923 16927 16928 16928 16927 16923 16918 16928 16924 16930 16928 16932 16932
16929 16927 16923 16926 16926 16928 16926 16923 16924 16926 16922 16927 16928 16934 16933

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 16923 bytes 100%
1,000 16922 bytes -1 byte 100%
10,000 16920 bytes -2 bytes 100%
100,000 16918 bytes -2 bytes 5.51%
1,000,000
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
16996 bytes +78 bytes (+0.46%) +53 bytes
16996 bytes +78 bytes (+0.46%) +53 bytes
16943 bytes +25 bytes (+0.15%)
16969 bytes +51 bytes (+0.30%) +26 bytes
17011 bytes +93 bytes (+0.55%) +68 bytes
17050 bytes +132 bytes (+0.78%) +107 bytes
17089 bytes +171 bytes (+1.01%) +146 bytes
17091 bytes +173 bytes (+1.02%) +148 bytes
17126 bytes +208 bytes (+1.23%) +183 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
Algorithm Program Parameters Size Compared To Best Zopfli
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 14476 bytes -2442 bytes (-14.43%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 14773 bytes -2145 bytes (-12.68%)
Brotli (Wikipedia) brotli brotli -q 11 15560 bytes -1358 bytes (-8.03%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 15674 bytes -1244 bytes (-7.35%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 16160 bytes -758 bytes (-4.48%)
LZMA2 (Wikipedia) xz xz -9 16688 bytes -230 bytes (-1.36%)
ZSTD (Wikipedia) zstd zstd -19 16954 bytes +36 bytes (+0.21%)

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):


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 2017.
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