Choose a version:
21% The original file has 641366 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 135618 bytes (132.4k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46856 bytes (45.8k)
CDN, direct link
cdnjs
  39934 bytes (39.0k)
CDN, direct link
gzip -6 (default)
  39598 bytes (38.7k)
local copy
unpkg
  39551 bytes (38.6k)
CDN, direct link
cdnhttps
  39539 bytes (38.6k)
CDN, direct link
jsdelivr
  39485 bytes (38.6k)
CDN, direct link
gzip -9
  39446 bytes (38.5k)
local copy
libdeflate -12
  38186 bytes (37.3k)
local copy
7zip -mx=9 -tgzip
  38133 bytes (37.2k)
local copy
pigz -11 -n
  38093 bytes (37.2k)
local copy
kzip -s0 -rn -b8
  38046 bytes (37.2k)
local copy
Zopfli
  37914 bytes (37.0k)
local copy
Zopfli (defluff)
  37912 bytes (37.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.3.min.js

You will automatically get the smallest React 0.14.3 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 1571 bytes by using my React 0.14.3 Zopfli version instead of the best available CDN (4.14% smaller than jsdelivr, 37914 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 --mls2 --bsr12 --lazy --ohh

(found November 19, 2015)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 2  --mls2
block splitting recursion 12  --bsr12
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 (37912 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.14.3.min.js --location | md5sum
c3207f7bf39699d4279ba404ea55f163  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.3.min.zopfli.js.gz | md5sum
c3207f7bf39699d4279ba404ea55f163  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.3.min.js --location | sha1sum
8a895678ccb6c6aad5d02f90bb2becb4106748ae  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.3.min.zopfli.js.gz | sha1sum
8a895678ccb6c6aad5d02f90bb2becb4106748ae  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46856 bytes c3207f7bf39699d4279ba404ea55f163 December 1, 2015 @ 11:25
cdnjs 39934 bytes c3207f7bf39699d4279ba404ea55f163 November 19, 2015 @ 07:05
unpkg 39551 bytes c3207f7bf39699d4279ba404ea55f163 July 11, 2016 @ 15:33
cdnhttps 39539 bytes c3207f7bf39699d4279ba404ea55f163 December 24, 2015 @ 07:35
jsdelivr 39485 bytes c3207f7bf39699d4279ba404ea55f163 November 19, 2015 @ 10:03

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
37914 bytes -5 bytes zopfli --i1000000 --mls2 --bsr12 --lazy --ohh November 19, 2015 @ 22:59
37919 bytes -5 bytes zopfli --i100000 --mls2 --bsr12 --lazy --ohh November 19, 2015 @ 15:14
37924 bytes -6 bytes zopfli --i10000 --mls2 --bsr12 --lazy --ohh November 19, 2015 @ 13:59
37930 bytes -15 bytes zopfli --i1000 --mls2 --bsr12 --lazy --ohh November 19, 2015 @ 13:54
37945 bytes zopfli --i100 --mls2 --bsr12 --lazy --ohh November 19, 2015 @ 13:48

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
37956 38042 38045 38042 38026 38042 38044 38044 38044 38044 38044 38038 38043 38040 38042
38043 38045 38044 38043 38041 38041 38040 38040 38040 38042 38049 38043 38059 38055 38040
37968 37964 38014 38011 38013 38016 38012 38043 38040 38044 38040 38048 38041 38040 38032
38027 37957 37939 38011 38016 38041 38005 38040 38040 38039 38041 38044 38041 38040 38042
37978 37980 37951 38016 38019 38015 38011 38041 38040 38039 38040 38044 38038 38040 38041
38043 38041 38040 38043 38040 38043 38039 38038 38039 38041 38039 38044 38050 38042 38041
37959 38043 38040 38040 38043 38041 38039 38038 38043 38044 38040 38040 38040 38040 38042
38012 38026 37935 38016 38023 38015 38012 38042 38040 38039 38040 38044 38045 38040 38042
37914 37970 38041 38019 38040 38011 38039 38038 38039 38039 38041 38043 38049 38039 38042
37943 37968 37956 37954 38022 38011 38003 38038 38043 38039 38039 38044 38046 38042 38051
37977 37971 38015 38019 37999 38016 38005 38038 38041 38039 38040 38043 38039 38042 38041
37930 38043 38042 37955 38039 38041 38040 38040 38040 38039 38042 38044 38045 38040 38041
37925 37970 38040 38017 38019 38010 38006 38038 38043 38039 38040 38044 38040 38042 38041
37962 38026 38019 37949 38011 37949 38005 38038 38040 38039 38040 38044 38045 38040 38041
37950 38039 38039 38040 38039 38041 38040 38043 38040 38044 38040 38044 38045 38040 38056
37962 37962 38018 38018 38022 38009 38008 38038 38040 38040 38038 38042 38040 38040 38042
37958 37970 37956 38019 38007 38019 38018 38038 38040 38044 38040 38043 38041 38041 38041
37958 37971 37958 38019 38011 38008 37943 38040 38040 38039 38042 38044 38041 38040 38041
37944 38041 37949 38020 38004 38019 38018 38040 38039 38039 38040 38040 38043 38042 38051
37963 37971 38017 38017 38008 38019 38018 38043 38040 38040 38040 38043 38041 38041 38041
37949 38043 38042 38009 38041 38039 38040 38040 38040 38039 38042 38040 38041 38042 38041
37964 38043 38043 38018 38019 38010 38001 38038 38042 38039 38042 38044 38043 38042 38041
37952 37963 37949 38017 38019 38019 38019 38038 38041 38044 38040 38044 38045 38040 38042

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 37945 bytes 100%
1,000 37930 bytes -15 bytes 100%
10,000 37924 bytes -6 bytes 100%
100,000 37919 bytes -5 bytes 0.87%
1,000,000 37914 bytes -5 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
38137 bytes +223 bytes (+0.59%) +91 bytes
38137 bytes +223 bytes (+0.59%) +91 bytes
38147 bytes +233 bytes (+0.61%) +101 bytes
38128 bytes +214 bytes (+0.56%) +82 bytes
38093 bytes +179 bytes (+0.47%) +47 bytes
38074 bytes +160 bytes (+0.42%) +28 bytes
38087 bytes +173 bytes (+0.46%) +41 bytes
38047 bytes +133 bytes (+0.35%) +1 byte
38046 bytes +132 bytes (+0.35%)

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 27929 bytes -9985 bytes (-26.34%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 30025 bytes -7889 bytes (-20.81%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31791 bytes -6123 bytes (-16.15%)
Brotli (Wikipedia) brotli brotli -q 11 33533 bytes -4381 bytes (-11.56%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33940 bytes -3974 bytes (-10.48%)
LZMA2 (Wikipedia) xz xz -9 34676 bytes -3238 bytes (-8.54%)
ZSTD (Wikipedia) zstd zstd -19 36141 bytes -1773 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