Choose a version:
21% The original file has 641356 bytes (626.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 135528 bytes (132.4k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46829 bytes (45.7k)
CDN, direct link
gzip -6 (default)
  39577 bytes (38.6k)
local copy
cdnhttps
  39531 bytes (38.6k)
CDN, direct link
cdnjs
  39531 bytes (38.6k)
CDN, direct link
jsdelivr
  39531 bytes (38.6k)
CDN, direct link
unpkg
  39531 bytes (38.6k)
CDN, direct link
gzip -9
  39425 bytes (38.5k)
local copy
libdeflate -12
  38137 bytes (37.2k)
local copy
7zip -mx=9 -tgzip
  38114 bytes (37.2k)
local copy
pigz -11 -n
  38075 bytes (37.2k)
local copy
kzip -s0 -rn -b7
  38025 bytes (37.1k)
local copy
Zopfli
  37897 bytes (37.0k)
local copy
Zopfli (defluff)
  37895 bytes (37.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.5.min.js

You will automatically get the smallest React 0.14.5 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 1634 bytes by using my React 0.14.5 Zopfli version instead of the best available CDN (4.31% smaller than unpkg, 37897 vs. 39531 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 --mls2 --bsr7 --lazy --ohh

(found December 30, 2015)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 2  --mls2
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 2 more bytes (37895 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.14.5.min.js --location | md5sum
77df40ebc8c9ee08a4cc758b84767eda  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.5.min.zopfli.js.gz | md5sum
77df40ebc8c9ee08a4cc758b84767eda  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.5.min.js --location | sha1sum
96b8eb2a5e7665bea075f53c3a88a625bfb08091  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.5.min.zopfli.js.gz | sha1sum
96b8eb2a5e7665bea075f53c3a88a625bfb08091  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46829 bytes 77df40ebc8c9ee08a4cc758b84767eda January 6, 2016 @ 18:22
cdnhttps 39531 bytes 77df40ebc8c9ee08a4cc758b84767eda November 22, 2016 @ 16:40
cdnjs 39531 bytes 77df40ebc8c9ee08a4cc758b84767eda January 3, 2016 @ 06:31
jsdelivr 39531 bytes 77df40ebc8c9ee08a4cc758b84767eda January 5, 2016 @ 18:16
unpkg 39531 bytes 77df40ebc8c9ee08a4cc758b84767eda July 11, 2016 @ 15:33

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
37897 bytes -2 bytes zopfli --i1000000 --mls2 --bsr7 --lazy --ohh December 30, 2015 @ 22:28
37899 bytes -5 bytes zopfli --i100000 --mls2 --bsr7 --lazy --ohh December 30, 2015 @ 11:24
37904 bytes -7 bytes zopfli --i10000 --mls2 --bsr7 --lazy --ohh December 30, 2015 @ 10:10
37911 bytes -3 bytes zopfli --i1000 --mls2 --bsr7 --lazy --ohh December 30, 2015 @ 10:04
37914 bytes -12 bytes zopfli --i1000 --mls2 --bsr12 --lazy --ohh December 30, 2015 @ 10:03
37926 bytes zopfli --i100 --mls2 --bsr12 --lazy --ohh December 30, 2015 @ 09:58

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

Most recent activity on November 22, 2016 @ 16:40.

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
37933 37941 38026 38024 38004 38023 38024 38024 38026 38026 38021 38024 38021 38026 38023
38021 38025 38025 38024 38020 38021 38023 38023 38022 38022 38027 38026 38026 38022 38020
37950 37928 37992 37990 37993 37992 38000 38021 38023 38020 38020 38020 38022 38020 38023
37897 38023 38024 37993 37990 38020 38020 38020 38024 38020 38020 38024 38024 38020 38024
37996 37951 37998 37992 37999 37927 37999 38023 38023 38021 38020 38020 38022 38020 38021
38023 38022 38025 38022 38022 38020 38021 38022 38023 38025 38022 38023 38026 38022 38021
38023 38023 38024 38020 38020 38020 38021 38020 38021 38020 38020 38023 38024 38020 38032
37920 37965 37914 37995 37930 37999 37984 38022 38023 38020 38020 38028 38026 38020 38021
37903 37937 37999 37997 37988 37981 37986 38022 38024 38021 38023 38028 38023 38020 38021
37942 37936 37927 38001 37988 37990 37982 38022 38024 38022 38020 38024 38025 38020 38021
37996 37915 37994 37998 37987 37982 37984 38022 38023 38020 38020 38027 38023 38022 38021
37916 38023 38024 37936 37918 38020 38023 38020 38023 38020 38023 38024 38026 38020 38021
38023 38023 38024 37997 37987 37935 37980 38022 38023 38020 38020 38025 38023 38026 38036
37939 37949 37928 37933 37987 37982 37984 38022 38023 38020 38020 38023 38024 38020 38024
37922 38022 38021 38020 37987 38021 38021 38021 38023 38021 38020 38023 38026 38020 38026
37954 37911 37998 37996 37987 37981 37994 38022 38023 38020 38022 38021 38023 38020 38024
37953 37944 37941 37998 37988 37927 37987 38020 38023 38020 38021 38023 38026 38020 38021
37954 37915 37994 37996 37988 37978 38000 38023 38020 38020 38022 38029 38022 38020 38021
37931 37931 38024 37955 37989 38001 37977 38020 38021 38024 38023 38023 38023 38020 38019
37910 37937 37928 37998 37999 37923 37981 38021 38021 38020 38020 38028 38023 38022 38021
37941 38023 38023 37929 37987 38020 38023 38020 38021 38021 38020 38020 38023 38020 38035
38023 38023 38023 37997 37988 38000 37991 38022 38022 38020 38023 38023 38027 38022 38024
37942 37937 37999 37973 37999 37982 37981 38022 38023 38021 38020 38023 38026 38020 38024

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 37926 bytes 100%
1,000 37911 bytes -15 bytes 100%
10,000 37904 bytes -7 bytes 100%
100,000 37899 bytes -5 bytes 0.58%
1,000,000 37897 bytes -2 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
38117 bytes +220 bytes (+0.58%) +92 bytes
38117 bytes +220 bytes (+0.58%) +92 bytes
38128 bytes +231 bytes (+0.61%) +103 bytes
38111 bytes +214 bytes (+0.56%) +86 bytes
38075 bytes +178 bytes (+0.47%) +50 bytes
38057 bytes +160 bytes (+0.42%) +32 bytes
38066 bytes +169 bytes (+0.45%) +41 bytes
38025 bytes +128 bytes (+0.34%)
38028 bytes +131 bytes (+0.35%) +3 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 27922 bytes -9975 bytes (-26.32%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 30019 bytes -7878 bytes (-20.79%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31832 bytes -6065 bytes (-16.00%)
Brotli (Wikipedia) brotli brotli -q 11 33499 bytes -4398 bytes (-11.61%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33942 bytes -3955 bytes (-10.44%)
LZMA2 (Wikipedia) xz xz -9 34644 bytes -3253 bytes (-8.58%)
ZSTD (Wikipedia) zstd zstd -19 36122 bytes -1775 bytes (-4.68%)

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