Choose a version:
21% The original file has 640047 bytes (625.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 135334 bytes (132.2k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46785 bytes (45.7k)
CDN
cdnjs
  39851 bytes (38.9k)
CDN
gzip -6 (default)
  39503 bytes (38.6k)
local copy
unpkg
  39464 bytes (38.5k)
CDN
cdnhttps
  39446 bytes (38.5k)
CDN
jsdelivr
  39393 bytes (38.5k)
CDN
gzip -9
  39352 bytes (38.4k)
local copy
libdeflate -12
  38057 bytes (37.2k)
local copy
7zip -mx=9 -tgzip
  38033 bytes (37.1k)
local copy
pigz -11 -n
  38003 bytes (37.1k)
local copy
kzip -s0 -rn -b7
  37934 bytes (37.0k)
local copy
Zopfli
  37825 bytes (36.9k)
local copy
Zopfli (defluff)
  37824 bytes (36.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.0.min.js (or via HTTPS)

You will automatically get the smallest React 0.14.0 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 1568 bytes by using my React 0.14.0 Zopfli version instead of the best available CDN (4.15% smaller than jsdelivr, 37825 vs. 39393 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 --mls4 --bsr25 --lazy --ohh

(found October 8, 2015)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 4  --mls4
block splitting recursion 25  --bsr25
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 (37824 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.14.0.min.js --location | md5sum
d84fecc741a8ac27a08494080164e77b  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-0.14.0.min.zopfli.js.gz | md5sum
d84fecc741a8ac27a08494080164e77b  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.0.min.js --location | sha1sum
c6d39062e267c86ed9026cf968c2fc5663c4c782  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-0.14.0.min.zopfli.js.gz | sha1sum
c6d39062e267c86ed9026cf968c2fc5663c4c782  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46785 bytes d84fecc741a8ac27a08494080164e77b October 10, 2015 @ 01:02
cdnjs 39851 bytes d84fecc741a8ac27a08494080164e77b October 8, 2015 @ 03:34
unpkg 39464 bytes d84fecc741a8ac27a08494080164e77b July 11, 2016 @ 15:33
cdnhttps 39446 bytes d84fecc741a8ac27a08494080164e77b December 24, 2015 @ 07:35
jsdelivr 39393 bytes d84fecc741a8ac27a08494080164e77b October 7, 2015 @ 19:36

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
37825 bytes -3 bytes zopfli --i1000000 --mls4 --bsr25 --lazy --ohh October 8, 2015 @ 18:04
37828 bytes -3 bytes zopfli --i100000 --mls4 --bsr25 --lazy --ohh October 8, 2015 @ 11:01
37831 bytes -1 byte zopfli --i10000 --mls4 --bsr25 --lazy --ohh October 8, 2015 @ 09:23
37832 bytes -3 bytes zopfli --i10000 --mls128 --bsr14 --lazy --ohh October 8, 2015 @ 07:18
37835 bytes -13 bytes zopfli --i1000 --mls128 --bsr14 --lazy --ohh October 8, 2015 @ 07:13
37848 bytes zopfli --i100 --mls128 --bsr14 --lazy --ohh October 8, 2015 @ 07:09

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
37860 37957 37957 37953 37931 37931 37961 37957 37957 37954 37957 37954 37953 37956 37956
37955 37955 37955 37955 37955 37953 37956 37954 37955 37954 37957 37956 37960 37966 37953
37865 37852 37955 37920 37920 37921 37956 37955 37954 37953 37954 37955 37955 37952 37952
37864 37954 37952 37826 37952 37922 37928 37952 37951 37954 37953 37955 37956 37955 37952
37920 37923 37952 37922 37856 37928 37957 37954 37954 37954 37954 37957 37953 37952 37967
37954 37952 37955 37957 37955 37954 37955 37954 37954 37954 37955 37952 37952 37952 37954
37955 37954 37952 37952 37952 37952 37954 37954 37951 37954 37953 37953 37954 37952 37952
37952 37858 37835 37829 37907 37919 37956 37952 37954 37954 37953 37953 37954 37952 37968
37869 37857 37955 37825 37910 37911 37953 37954 37952 37952 37954 37956 37960 37955 37952
37858 37861 37952 37926 37914 37928 37957 37955 37954 37954 37952 37954 37957 37952 37959
37869 37847 37952 37827 37835 37912 37826 37954 37952 37952 37953 37955 37958 37952 37952
37865 37853 37955 37839 37952 37851 37954 37952 37953 37952 37953 37955 37959 37953 37954
37859 37856 37952 37927 37907 37928 37957 37955 37951 37954 37953 37955 37959 37952 37952
37859 37848 37952 37857 37912 37917 37957 37954 37954 37954 37953 37953 37954 37952 37954
37852 37951 37951 37928 37955 37954 37953 37954 37954 37954 37954 37953 37959 37952 37957
37860 37855 37829 37846 37911 37909 37953 37952 37954 37953 37954 37952 37952 37954 37954
37865 37849 37952 37865 37907 37920 37917 37954 37954 37953 37952 37954 37958 37953 37952
37922 37854 37952 37868 37827 37919 37953 37952 37951 37953 37952 37954 37956 37952 37956
37866 37841 37955 37841 37846 37928 37954 37954 37954 37952 37952 37952 37955 37952 37952
37856 37854 37952 37828 37909 37918 37953 37952 37954 37955 37955 37952 37957 37952 37952
37854 37825 37952 37928 37952 37952 37953 37952 37954 37952 37953 37955 37953 37952 37953
37866 37853 37952 37831 37908 37928 37953 37954 37954 37954 37953 37953 37953 37952 37952
37850 37848 37833 37838 37909 37929 37930 37954 37954 37953 37954 37953 37959 37954 37952

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 37848 bytes 100%
1,000 37834 bytes -14 bytes 100%
10,000 37831 bytes -3 bytes 100%
100,000 37828 bytes -3 bytes 2.90%
1,000,000 37825 bytes -3 bytes 2.61%
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
38045 bytes +220 bytes (+0.58%) +111 bytes
38047 bytes +222 bytes (+0.59%) +113 bytes
38058 bytes +233 bytes (+0.62%) +124 bytes
38035 bytes +210 bytes (+0.56%) +101 bytes
37999 bytes +174 bytes (+0.46%) +65 bytes
38009 bytes +184 bytes (+0.49%) +75 bytes
37946 bytes +121 bytes (+0.32%) +12 bytes
37934 bytes +109 bytes (+0.29%)
37940 bytes +115 bytes (+0.30%) +6 bytes

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 27863 bytes -9962 bytes (-26.34%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 29948 bytes -7877 bytes (-20.82%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31772 bytes -6053 bytes (-16.00%)
Brotli (Wikipedia) brotli brotli -q 11 33442 bytes -4383 bytes (-11.59%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33859 bytes -3966 bytes (-10.49%)
LZMA2 (Wikipedia) xz xz -9 34576 bytes -3249 bytes (-8.59%)
Zstandard (Wikipedia) zstd zstd -19 36041 bytes -1784 bytes (-4.72%)

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