Choose a version:
21% The original file has 641672 bytes (626.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 135647 bytes (132.5k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46873 bytes (45.8k)
CDN, direct link
cdnjs
  39942 bytes (39.0k)
CDN, direct link
gzip -6 (default)
  39599 bytes (38.7k)
local copy
cdnhttps
  39548 bytes (38.6k)
CDN, direct link
unpkg
  39548 bytes (38.6k)
CDN, direct link
gzip -9
  39441 bytes (38.5k)
local copy
libdeflate -12
  38145 bytes (37.3k)
local copy
7zip -mx=9 -tgzip
  38127 bytes (37.2k)
local copy
pigz -11 -n
  38080 bytes (37.2k)
local copy
kzip -s0 -rn -b8
  38043 bytes (37.2k)
local copy
Zopfli
  37911 bytes (37.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.8.min.js

You will automatically get the smallest React 0.14.8 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 1637 bytes by using my React 0.14.8 Zopfli version instead of the best available CDN (4.32% smaller than unpkg, 37911 vs. 39548 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 --bsr14 --lazy --ohh

(found March 30, 2016)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 16  --mls16
block splitting recursion 14  --bsr14
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-0.14.8.min.js --location | md5sum
f1e7c902d1851c39a0ad007a0b7c5ed7  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.8.min.zopfli.js.gz | md5sum
f1e7c902d1851c39a0ad007a0b7c5ed7  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.8.min.js --location | sha1sum
62a0ecfd72a5692da3abb5e27f2b46b33e9657db  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.14.8.min.zopfli.js.gz | sha1sum
62a0ecfd72a5692da3abb5e27f2b46b33e9657db  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46873 bytes f1e7c902d1851c39a0ad007a0b7c5ed7 May 6, 2016 @ 13:19
cdnjs 39942 bytes f1e7c902d1851c39a0ad007a0b7c5ed7 March 29, 2016 @ 19:02
cdnhttps 39548 bytes f1e7c902d1851c39a0ad007a0b7c5ed7 November 22, 2016 @ 16:40
unpkg 39548 bytes f1e7c902d1851c39a0ad007a0b7c5ed7 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
37911 bytes -4 bytes zopfli --i1000000 --mls16 --bsr14 --lazy --ohh March 30, 2016 @ 19:40
37915 bytes -1 byte zopfli --i100000 --mls16 --bsr14 --lazy --ohh March 29, 2016 @ 21:02
37916 bytes -3 bytes zopfli --i100000 --mls4 --bsr19 --lazy --ohh March 29, 2016 @ 19:55
37919 bytes -8 bytes zopfli --i10000 --mls4 --bsr19 --lazy --ohh March 29, 2016 @ 18:55
37927 bytes -14 bytes zopfli --i1000 --mls4 --bsr19 --lazy --ohh March 29, 2016 @ 18:49
37941 bytes zopfli --i100 --mls4 --bsr19 --lazy --ohh March 29, 2016 @ 18:48

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 37951 38041 38040 38015 38018 38042 38040 38041 38038 38036 38038 38039 38038 38038
38038 38038 38039 38038 38038 38039 38039 38039 38038 38041 38042 38042 38039 38040 38038
37944 37955 38003 38004 38004 38005 38039 38037 38038 38038 38036 38043 38038 38038 38037
37944 38038 38040 38006 38011 37993 38013 38037 38038 38038 38036 38041 38038 38038 38038
37960 37969 38010 38005 38011 37939 38006 38038 38038 38038 38036 38043 38036 38038 38038
38038 38039 38038 38038 38039 38038 38038 38037 38037 38040 38036 38043 38036 38036 38038
38038 38038 38039 38038 38038 38038 38038 38037 38040 38038 38036 38038 38037 38035 38037
38037 38037 37926 38006 38001 38012 38012 38041 38038 38038 38036 38038 38038 38041 38038
37950 38003 37937 38006 38000 37990 38014 38037 38036 38038 38037 38039 38040 38043 38038
37954 37955 37941 37942 38013 38011 38013 38037 38040 38037 38038 38039 38038 38038 38044
38008 37949 37940 37911 37996 37993 37999 38037 38037 38038 38039 38040 38037 38041 38038
37946 38038 38038 37947 38038 38039 38039 38037 38038 38038 38036 38040 38038 38038 38038
38041 37958 38040 37934 38001 37993 37937 38037 38038 38038 38036 38039 38037 38037 38036
37957 37949 37940 37940 38001 37993 38011 38037 38038 38038 38037 38038 38038 38041 38038
37944 38038 38038 37934 38038 38038 38039 38039 38037 38038 38039 38039 38038 38038 38039
37962 37916 37939 38009 37997 37991 38006 38037 38037 38039 38036 38039 38037 38038 38038
37946 37953 37946 37933 38005 37937 38011 38037 38038 38038 38036 38040 38038 38036 38038
37986 37953 37947 38009 38011 37995 38010 38038 38039 38038 38037 38036 38038 38038 38038
37942 37945 38040 37945 37999 38011 38011 38037 38037 38039 38037 38037 38036 38036 38037
37946 37953 38039 37963 37999 37938 38011 38037 38038 38038 38036 38041 38038 38041 38038
37939 37921 38039 37939 38039 38038 38038 38037 38037 38038 38039 38038 38038 38042 38041
37932 38038 38038 37934 37997 38013 38012 38037 38038 38038 38038 38041 38036 38042 38038
37920 37954 37938 37986 38011 38012 38012 38037 38038 38038 38036 38043 38038 38041 38038

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 37941 bytes 100%
1,000 37926 bytes -15 bytes 100%
10,000 37919 bytes -7 bytes 100%
100,000 37915 bytes -4 bytes 0.58%
1,000,000 37911 bytes -4 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
38138 bytes +227 bytes (+0.60%) +95 bytes
38142 bytes +231 bytes (+0.61%) +99 bytes
38148 bytes +237 bytes (+0.63%) +105 bytes
38131 bytes +220 bytes (+0.58%) +88 bytes
38093 bytes +182 bytes (+0.48%) +50 bytes
38079 bytes +168 bytes (+0.44%) +36 bytes
38086 bytes +175 bytes (+0.46%) +43 bytes
38045 bytes +134 bytes (+0.35%) +2 bytes
38043 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 27935 bytes -9976 bytes (-26.31%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 30027 bytes -7884 bytes (-20.80%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31825 bytes -6086 bytes (-16.05%)
Brotli (Wikipedia) brotli brotli -q 11 33543 bytes -4368 bytes (-11.52%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33934 bytes -3977 bytes (-10.49%)
LZMA2 (Wikipedia) xz xz -9 34692 bytes -3219 bytes (-8.49%)
ZSTD (Wikipedia) zstd zstd -19 36140 bytes -1771 bytes (-4.67%)

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