Choose a version:
21% The original file has 641226 bytes (626.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 135543 bytes (132.4k, 21%).

After GZIP compression these minified files vary in size:
Boot
  46823 bytes (45.7k)
CDN
jsdelivr
  46823 bytes (45.7k)
CDN
cdnjs
  39914 bytes (39.0k)
CDN
gzip -6 (default)
  39577 bytes (38.6k)
local copy
unpkg
  39534 bytes (38.6k)
CDN
cdnhttps
  39518 bytes (38.6k)
CDN
gzip -9
  39426 bytes (38.5k)
local copy
libdeflate -12
  38150 bytes (37.3k)
local copy
7zip -mx=9 -tgzip
  38109 bytes (37.2k)
local copy
pigz -11 -n
  38071 bytes (37.2k)
local copy
kzip -s0 -rn -b8
  38027 bytes (37.1k)
local copy
Zopfli
  37905 bytes (37.0k)
local copy
Zopfli (defluff)
  37904 bytes (37.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.14.2.min.js (or via HTTPS)

You will automatically get the smallest React 0.14.2 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 1613 bytes by using my React 0.14.2 Zopfli version instead of the best available CDN (4.26% smaller than cdnhttps, 37905 vs. 39518 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 --bsr21 --lazy --ohh

(found November 3, 2015)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 2  --mls2
block splitting recursion 21  --bsr21
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 (37904 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.14.2.min.js --location | md5sum
36dee7e10e15906c4f3b5b0db8667d95  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-0.14.2.min.zopfli.js.gz | md5sum
36dee7e10e15906c4f3b5b0db8667d95  -

SHA1:
curl --silent --compressed https://fb.me/react-0.14.2.min.js --location | sha1sum
c03f74b30aa4430c81b18c141e06de92e3515d31  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-0.14.2.min.zopfli.js.gz | sha1sum
c03f74b30aa4430c81b18c141e06de92e3515d31  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 46823 bytes 36dee7e10e15906c4f3b5b0db8667d95 November 5, 2015 @ 07:54
jsdelivr 46823 bytes 36dee7e10e15906c4f3b5b0db8667d95 November 2, 2015 @ 21:07
cdnjs 39914 bytes 36dee7e10e15906c4f3b5b0db8667d95 November 3, 2015 @ 02:50
unpkg 39534 bytes 36dee7e10e15906c4f3b5b0db8667d95 July 11, 2016 @ 15:33
cdnhttps 39518 bytes 36dee7e10e15906c4f3b5b0db8667d95 December 24, 2015 @ 07:35

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
37905 bytes -3 bytes zopfli --i1000000 --mls2 --bsr21 --lazy --ohh November 3, 2015 @ 20:38
37908 bytes -6 bytes zopfli --i100000 --mls2 --bsr21 --lazy --ohh November 3, 2015 @ 12:04
37914 bytes -10 bytes zopfli --i10000 --mls2 --bsr21 --lazy --ohh November 3, 2015 @ 11:01
37924 bytes -1 byte zopfli --i1000 --mls2 --bsr21 --lazy --ohh November 3, 2015 @ 10:42
37925 bytes -10 bytes zopfli --i1000 --mls8 --bsr13 --lazy --ohh November 3, 2015 @ 10:25
37935 bytes -5 bytes zopfli --i1000 --mls8 --bsr17 --lazy --ohh November 3, 2015 @ 10:22
37940 bytes zopfli --i100 --mls2 --bsr13 --lazy --ohh November 3, 2015 @ 10:19

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
37936 37943 38027 38024 38006 38025 38025 38021 38021 38025 38024 38019 38019 38025 38021
38024 38021 38024 38020 38021 38022 38020 38021 38022 38023 38025 38026 38024 38022 38023
37948 37954 37992 37994 38002 37992 38004 38020 38023 38023 38022 38028 38022 38020 38021
37937 37935 38023 37980 37993 37995 37985 38022 38020 38020 38021 38022 38022 38020 38033
37946 37951 37933 37997 37996 37937 37984 38020 38023 38021 38020 38020 38021 38020 38020
38023 38021 38023 38022 38023 38020 38019 38020 38023 38021 38022 38020 38019 38021 38020
38023 38020 38021 38024 38023 38020 38018 38024 38019 38021 38022 38024 38024 38021 38020
37922 37945 38000 38000 38001 37997 38000 38020 38023 38021 38020 38023 38021 38020 38020
37939 38021 38023 38020 38021 38020 38020 38020 38021 38021 38022 38023 38021 38019 38020
37913 37948 37908 38000 37994 38002 37987 38022 38025 38023 38024 38024 38024 38021 38020
37995 37944 38002 38001 37979 37986 37990 38020 38023 38021 38020 38020 38027 38020 38032
37944 38021 38021 37937 38023 38022 38021 38020 38023 38021 38021 38026 38026 38021 38032
38023 38021 38021 37999 37988 37993 37924 38020 38023 38021 38021 38023 38027 38020 38020
37947 38001 37930 37994 37990 37990 37987 38019 38019 38021 38019 38026 38026 38020 38020
37931 38020 38020 37996 38023 38020 38021 38022 38023 38021 38021 38026 38028 38020 38019
37925 37937 37930 38001 37995 37996 37996 38020 38019 38021 38021 38020 38021 38020 38022
37962 37943 37939 37999 37998 38001 38001 38020 38019 38022 38020 38023 38024 38020 38022
37905 37942 37995 37999 37994 37982 38000 38020 38022 38022 38022 38023 38020 38019 38022
37934 38023 38023 38005 37990 37939 38001 38022 38022 38020 38021 38023 38021 38024 38020
37939 37941 37933 38000 37989 37992 38002 38020 38023 38021 38021 38028 38029 38021 38020
37944 38021 38021 38022 38021 38019 38019 38020 38023 38023 38022 38019 38024 38019 38020
37958 38021 38021 38000 37992 37933 38020 38020 38023 38021 38021 38022 38024 38021 38020
37960 37940 37930 37938 37995 37993 38001 38020 38019 38021 38020 38026 38027 38020 38020

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 37940 bytes 100%
1,000 37924 bytes -16 bytes 100%
10,000 37914 bytes -10 bytes 100%
100,000 37908 bytes -6 bytes 1.74%
1,000,000 37905 bytes -3 bytes 0.58%
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 +212 bytes (+0.56%) +90 bytes
38116 bytes +211 bytes (+0.56%) +89 bytes
38127 bytes +222 bytes (+0.59%) +100 bytes
38106 bytes +201 bytes (+0.53%) +79 bytes
38074 bytes +169 bytes (+0.45%) +47 bytes
38057 bytes +152 bytes (+0.40%) +30 bytes
38065 bytes +160 bytes (+0.42%) +38 bytes
38029 bytes +124 bytes (+0.33%) +2 bytes
38027 bytes +122 bytes (+0.32%)

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 27906 bytes -9999 bytes (-26.38%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 30010 bytes -7895 bytes (-20.83%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 31832 bytes -6073 bytes (-16.02%)
Brotli (Wikipedia) brotli brotli -q 11 33584 bytes -4321 bytes (-11.40%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 33916 bytes -3989 bytes (-10.52%)
LZMA2 (Wikipedia) xz xz -9 34656 bytes -3249 bytes (-8.57%)
Zstandard (Wikipedia) zstd zstd -19 36117 bytes -1788 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