Choose a version:
21% The original file has 641479 bytes (626.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 135572 bytes (132.4k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46841 bytes (45.7k)
CDN
cdnjs
  45495 bytes (44.4k)
CDN
gzip -6 (default)
  39587 bytes (38.7k)
local copy
cdnhttps
  39542 bytes (38.6k)
CDN
unpkg
  39542 bytes (38.6k)
CDN
gzip -9
  39435 bytes (38.5k)
local copy
libdeflate -12
  38146 bytes (37.3k)
local copy
7zip -mx=9 -tgzip
  38123 bytes (37.2k)
local copy
pigz -11 -n
  38086 bytes (37.2k)
local copy
kzip -s0 -rn -b8
  38036 bytes (37.1k)
local copy
Zopfli
  37910 bytes (37.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.6.min.js (or via HTTPS)

You will automatically get the smallest React 0.14.6 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 1632 bytes by using my React 0.14.6 Zopfli version instead of the best available CDN (4.30% smaller than unpkg, 37910 vs. 39542 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 January 8, 2016)
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

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.14.6.min.js --location | md5sum
e7476f6d44ee6ea712186f06e47654f2  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-0.14.6.min.zopfli.js.gz | md5sum
e7476f6d44ee6ea712186f06e47654f2  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.6.min.js --location | sha1sum
218c85780b2e55a8f51488e6b0efc676869f8337  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-0.14.6.min.zopfli.js.gz | sha1sum
218c85780b2e55a8f51488e6b0efc676869f8337  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46841 bytes e7476f6d44ee6ea712186f06e47654f2 January 10, 2016 @ 19:46
cdnjs 45495 bytes e7476f6d44ee6ea712186f06e47654f2 January 7, 2016 @ 05:16
cdnhttps 39542 bytes e7476f6d44ee6ea712186f06e47654f2 November 22, 2016 @ 16:40
unpkg 39542 bytes e7476f6d44ee6ea712186f06e47654f2 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:

16.6.1, 16.6.0,
16.5.2, 16.5.1, 16.5.0,
16.4.2, 16.4.1, 16.4.0,
16.3.2, 16.3.1, 16.3.0,
16.2.0,
16.1.1, 16.1.0, 16.0.0,
15.6.2, 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
37910 bytes -3 bytes zopfli --i1000000 --mls2 --bsr12 --lazy --ohh January 8, 2016 @ 06:12
37913 bytes -5 bytes zopfli --i100000 --mls2 --bsr12 --lazy --ohh January 7, 2016 @ 19:56
37918 bytes -10 bytes zopfli --i10000 --mls2 --bsr12 --lazy --ohh January 7, 2016 @ 18:26
37928 bytes -1 byte zopfli --i1000 --mls2 --bsr12 --lazy --ohh January 7, 2016 @ 17:56
37929 bytes -17 bytes zopfli --i1000 --mls4 --bsr19 --lazy --ohh January 7, 2016 @ 17:53
37946 bytes zopfli --i100 --mls4 --bsr19 --lazy --ohh January 7, 2016 @ 17:50

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
37947 38034 38038 38033 38014 38015 38037 38034 38034 38036 38032 38030 38031 38032 38048
38035 38035 38031 38030 38030 38032 38032 38033 38035 38032 38036 38039 38037 38035 38032
37958 37942 38002 38003 38005 38002 38010 38031 38036 38030 38032 38029 38033 38030 38033
37925 38031 38035 38003 38013 37991 38011 38033 38036 38033 38032 38030 38030 38030 38030
37954 37959 38009 38004 38008 37941 38000 38031 38032 38030 38032 38030 38030 38030 38042
38032 38035 38035 38032 38031 38032 38030 38030 38032 38032 38031 38030 38036 38032 38032
38032 38031 38036 38030 38030 38032 38030 38030 38030 38030 38032 38031 38030 38030 38030
37930 37940 37925 38005 38004 38010 37994 38030 38036 38030 38032 38030 38033 38030 38030
37910 37960 38035 38031 37999 37993 38030 38030 38032 38040 38030 38032 38036 38033 38031
37951 37946 37941 38011 38004 38001 37992 38030 38030 38030 38031 38032 38033 38030 38030
38007 37951 38003 38008 37997 37992 37994 38030 38032 38030 38031 38033 38030 38032 38030
37944 38031 38035 37947 37995 38032 38031 38033 38030 38033 38032 38030 38033 38030 38032
38035 38034 38035 38006 37996 37990 37991 38030 38031 38030 38032 38031 38031 38030 38032
37949 37959 37940 37944 37996 37994 37994 38030 38036 38030 38033 38030 38033 38030 38031
37932 38034 38032 38030 37997 38031 38032 38031 38032 38040 38031 38032 38033 38030 38033
37923 37916 38008 38006 37997 37991 38004 38030 38032 38031 38033 38030 38030 38030 38030
37964 37955 37950 38008 37999 37937 37997 38030 38036 38030 38032 38032 38033 38030 38030
37963 37924 38004 38006 37999 37988 38010 38031 38033 38030 38030 38033 38033 38030 38032
37942 37942 38036 38007 37998 38011 37992 38033 38032 38033 38030 38031 38033 38034 38029
37916 37947 37938 38008 38008 37934 37993 38031 38030 38031 38032 38033 38033 38032 38032
37950 38034 38033 37939 38032 38032 38030 38033 38032 38040 38031 38030 38033 38034 38043
38032 38031 38034 38007 38000 38012 38001 38030 38031 38030 38031 38033 38030 38032 38033
37953 37949 37938 37984 38008 37990 37992 38030 38036 38040 38032 38030 38033 38030 38046

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 37935 bytes 100%
1,000 37928 bytes -7 bytes 100%
10,000 37918 bytes -10 bytes 100%
100,000 37913 bytes -5 bytes 0.87%
1,000,000 37910 bytes -3 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
38126 bytes +216 bytes (+0.57%) +90 bytes
38128 bytes +218 bytes (+0.58%) +92 bytes
38138 bytes +228 bytes (+0.60%) +102 bytes
38120 bytes +210 bytes (+0.55%) +84 bytes
38085 bytes +175 bytes (+0.46%) +49 bytes
38068 bytes +158 bytes (+0.42%) +32 bytes
38074 bytes +164 bytes (+0.43%) +38 bytes
38039 bytes +129 bytes (+0.34%) +3 bytes
38036 bytes +126 bytes (+0.33%)

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 - but your browser doesn't support it.
Algorithm Program Parameters Size Compared To Best Zopfli
ZPAQ (Wikipedia) zpaq zpaq -method 69 27928 bytes -9982 bytes (-26.33%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 30027 bytes -7883 bytes (-20.79%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31838 bytes -6072 bytes (-16.02%)
Brotli (Wikipedia) brotli brotli -q 11 33522 bytes -4388 bytes (-11.57%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33921 bytes -3989 bytes (-10.52%)
LZMA2 (Wikipedia) xz xz -9 34656 bytes -3254 bytes (-8.58%)
Zstandard (Wikipedia) zstd zstd -19 36131 bytes -1779 bytes (-4.69%)

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 2018.
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