Choose a version:
21% The original file has 640971 bytes (625.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 135480 bytes (132.3k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46797 bytes (45.7k)
CDN, direct link
jsdelivr
  46797 bytes (45.7k)
CDN, direct link
cdnjs
  39885 bytes (39.0k)
CDN, direct link
gzip -6 (default)
  39542 bytes (38.6k)
local copy
unpkg
  39502 bytes (38.6k)
CDN, direct link
cdnhttps
  39485 bytes (38.6k)
CDN, direct link
gzip -9
  39391 bytes (38.5k)
local copy
libdeflate -12
  38116 bytes (37.2k)
local copy
7zip -mx=9 -tgzip
  38076 bytes (37.2k)
local copy
pigz -11 -n
  38036 bytes (37.1k)
local copy
kzip -s0 -rn -b7
  37978 bytes (37.1k)
local copy
Zopfli
  37868 bytes (37.0k)
local copy
Zopfli (defluff)
  37867 bytes (37.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.1.min.js

You will automatically get the smallest React 0.14.1 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 1617 bytes by using my React 0.14.1 Zopfli version instead of the best available CDN (4.27% smaller than cdnhttps, 37868 vs. 39485 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 --i1000000 --mb8 --mls16 --bsr7 --lazy --ohh

(found October 29, 2015)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 16  --mls16
block splitting recursion 7  --bsr7
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 (37867 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.14.1.min.js --location | md5sum
1e9b388def14ce60f1770c91f1422cb0  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.1.min.zopfli.js.gz | md5sum
1e9b388def14ce60f1770c91f1422cb0  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.1.min.js --location | sha1sum
e3a1417e8b79db31e586090e1ce80bf245a5f793  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.1.min.zopfli.js.gz | sha1sum
e3a1417e8b79db31e586090e1ce80bf245a5f793  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46797 bytes 1e9b388def14ce60f1770c91f1422cb0 October 30, 2015 @ 02:59
jsdelivr 46797 bytes 1e9b388def14ce60f1770c91f1422cb0 October 28, 2015 @ 23:05
cdnjs 39885 bytes 1e9b388def14ce60f1770c91f1422cb0 October 29, 2015 @ 06:04
unpkg 39502 bytes 1e9b388def14ce60f1770c91f1422cb0 July 11, 2016 @ 15:33
cdnhttps 39485 bytes 1e9b388def14ce60f1770c91f1422cb0 December 24, 2015 @ 07:35

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

Other Versions

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

15.6.1, 15.6.0,
15.5.2, 15.5.1, 15.5.0,
15.4.2, 15.4.1, 15.4.0,
15.3.2, 15.3.1, 15.3.0,
15.2.1, 15.2.0,
15.1.0,
15.0.2, 15.0.1, 15.0.0,
0.14.8, 0.14.7, 0.14.6, 0.14.5, 0.14.4, 0.14.3, 0.14.2, 0.14.1, 0.14.0,
0.13.3, 0.13.2, 0.13.1, 0.13.0,
0.12.2, 0.12.1, 0.12.0,
0.11.2, 0.11.1, 0.11.0,
0.10.0

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, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
37868 bytes -1 byte zopfli --i1000000 --mls16 --bsr7 --lazy --ohh October 29, 2015 @ 22:29
37869 bytes -5 bytes zopfli --i100000 --mls16 --bsr7 --lazy --ohh October 29, 2015 @ 14:27
37874 bytes -3 bytes zopfli --i10000 --mls16 --bsr7 --lazy --ohh October 29, 2015 @ 13:31
37877 bytes -6 bytes zopfli --i10000 --mls2 --bsr25 --lazy --ohh October 29, 2015 @ 13:18
37883 bytes -2 bytes zopfli --i10000 --mls8 --bsr7 --lazy --ohh October 29, 2015 @ 13:18
37885 bytes -12 bytes zopfli --i1000 --mls2 --bsr25 --lazy --ohh October 29, 2015 @ 13:14
37897 bytes zopfli --i100 --mls16 --bsr7 --lazy --ohh October 29, 2015 @ 13:11

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 @ 15:33.

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
37920 37910 37994 37995 37975 37993 37997 37996 37996 37996 37993 37992 37996 37994 37995
37993 37996 37994 37995 37993 37995 37994 37995 37993 37996 37999 38000 37998 38000 37995
37905 37919 37962 37963 37962 37962 37962 37995 37995 37994 37995 38003 37999 37995 37994
37873 37994 37878 37868 37960 37971 37952 37994 37994 37995 37995 37995 37996 37995 37995
37903 37920 37908 37966 37970 37901 37967 37997 37995 37995 37994 37995 37996 37995 37995
37995 37997 37996 37995 37994 37995 37995 37994 37995 37995 37995 37992 37995 37995 37995
37995 37994 37995 37993 37995 37995 37995 37995 37995 37995 37996 37999 37996 37995 37995
37903 37902 37995 37969 37970 37947 37965 37994 37995 37994 37995 37995 37996 37994 37995
37909 37905 37995 37969 37993 37995 37957 37994 37994 37994 37995 37999 37995 37995 37994
37883 37910 37906 37899 37970 37971 37970 37994 37994 37995 37994 37995 38002 37992 37995
37966 37916 37967 37969 37960 37953 37957 37995 37993 37995 37995 37999 37996 37994 37995
37902 37996 37995 37880 37995 37995 37995 37994 37996 37995 37995 37995 38001 37994 38004
37911 37906 37995 37969 37969 37957 37902 37995 37995 37995 37996 37995 38002 37994 37994
37917 37972 37900 37907 37957 37963 37951 37994 37994 37994 37994 37995 38000 37994 37994
37900 37994 37994 37992 37994 37995 37995 37994 37994 37994 37994 37999 37996 37994 37995
37909 37907 37905 37969 37958 37971 37963 37994 37994 37995 37995 38000 37996 37994 37995
37925 37925 37908 37969 37970 37971 37960 37994 37994 37995 37995 37995 37996 37992 37995
37911 37912 37894 37970 37958 37962 37970 37994 37992 37995 37994 38000 37996 37995 37995
37898 37905 37901 37903 37959 37971 37971 37995 37993 37995 37995 37999 37996 37995 37995
37908 37933 37904 37884 37970 37963 37896 37995 37994 37996 37994 37999 37994 37993 37995
37872 37905 37993 37900 37995 37995 37995 37995 37994 37995 37993 37995 37995 37995 37995
37927 37994 37992 37903 37959 37963 37953 37995 37992 37995 37996 37992 37997 37995 37995
37904 37906 37900 37961 37969 37971 37963 37994 37994 37995 37994 37999 37996 37994 37995

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 37897 bytes 100%
1,000 37879 bytes -18 bytes 100%
10,000 37874 bytes -5 bytes 100%
100,000 37869 bytes -5 bytes 2.03%
1,000,000 37868 bytes -1 byte 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
38089 bytes +221 bytes (+0.58%) +111 bytes
38087 bytes +219 bytes (+0.58%) +109 bytes
38101 bytes +233 bytes (+0.62%) +123 bytes
38079 bytes +211 bytes (+0.56%) +101 bytes
38041 bytes +173 bytes (+0.46%) +63 bytes
38024 bytes +156 bytes (+0.41%) +46 bytes
38036 bytes +168 bytes (+0.44%) +58 bytes
37978 bytes +110 bytes (+0.29%)
37982 bytes +114 bytes (+0.30%) +4 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
ZPAQ (Wikipedia) zpaq zpaq -method 69 27889 bytes -9979 bytes (-26.35%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 29983 bytes -7885 bytes (-20.82%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31797 bytes -6071 bytes (-16.03%)
Brotli (Wikipedia) brotli brotli -q 11 33538 bytes -4330 bytes (-11.43%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33908 bytes -3960 bytes (-10.46%)
LZMA2 (Wikipedia) xz xz -9 34624 bytes -3244 bytes (-8.57%)
ZSTD (Wikipedia) zstd zstd -19 36086 bytes -1782 bytes (-4.71%)

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