Choose a version:
21% The original file has 592869 bytes (579.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 126275 bytes (123.3k, 21%).

After GZIP compression these minified files vary in size:
Boot
  42160 bytes (41.2k)
CDN
cdnjs
  35323 bytes (34.5k)
CDN
gzip -6 (default)
  34806 bytes (34.0k)
local copy
cdnhttps
  34786 bytes (34.0k)
CDN
unpkg
  34688 bytes (33.9k)
CDN
jsdelivr
  34637 bytes (33.8k)
CDN
gzip -9
  34596 bytes (33.8k)
local copy
7zip -mx=9 -tgzip
  33560 bytes (32.8k)
local copy
libdeflate -12
  33535 bytes (32.7k)
local copy
kzip -s0 -rn -b1
  33496 bytes (32.7k)
local copy
pigz -11 -n
  33431 bytes (32.6k)
local copy
Zopfli
  33413 bytes (32.6k)
local copy
Zopfli (defluff)
  33412 bytes (32.6k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.11.0.min.js

You will automatically get the smallest React 0.11.0 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 1224 bytes by using my React 0.11.0 Zopfli version instead of the best available CDN (3.66% smaller than jsdelivr, 33413 vs. 34637 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 --i100000 --mb8 --mls128 --bsr18 --lazy --ohh

(found December 17, 2015)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 128  --mls128
block splitting recursion 18  --bsr18
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 (33412 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-0.11.0.min.js --location | md5sum
793e9091d759920eba410c52f1b1eea6  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.11.0.min.zopfli.js.gz | md5sum
793e9091d759920eba410c52f1b1eea6  -

SHA1:
curl --silent --compressed https://fb.me/react-0.11.0.min.js --location | sha1sum
d375991559a922582dc6460c878f66b83e05c657  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.11.0.min.zopfli.js.gz | sha1sum
d375991559a922582dc6460c878f66b83e05c657  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 42160 bytes 793e9091d759920eba410c52f1b1eea6 March 20, 2015 @ 16:47
cdnjs 35323 bytes 793e9091d759920eba410c52f1b1eea6 July 18, 2014 @ 02:15
cdnhttps 34786 bytes 793e9091d759920eba410c52f1b1eea6 December 24, 2015 @ 07:35
unpkg 34688 bytes 793e9091d759920eba410c52f1b1eea6 July 11, 2016 @ 15:34
jsdelivr 34637 bytes 793e9091d759920eba410c52f1b1eea6 August 7, 2014 @ 20:33

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available React versions at minime.stephan-brumme.com:

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
33413 bytes -1 byte zopfli --i100000 --mls128 --bsr18 --lazy --ohh December 17, 2015 @ 12:57
33414 bytes -1 byte zopfli --i10000 --mls128 --bsr16 --lazy --ohh September 17, 2015 @ 08:24
33415 bytes -1 byte zopfli --i1000 --mls128 --bsr16 --lazy --ohh September 14, 2015 @ 19:28
33416 bytes -1 byte zopfli --i1000 --mls128 --bsr4 --lazy --ohh September 14, 2015 @ 19:22
33417 bytes -5 bytes zopfli --i1000 --mls64 --bsr7 --lazy --ohh September 14, 2015 @ 19:20
33422 bytes zopfli --i100 --mls128 --bsr16 --lazy --ohh September 14, 2015 @ 12:07

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 @ 15:34.

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 or 100,000.
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
33423 33423 33431 33428 33428 33427 33419 33418 33417 33431 33416 33431 33436 33435 33428
33434 33433 33429 33428 33422 33427 33416 33427 33416 33423 33418 33417 33435 33433 33419
33431 33429 33427 33425 33417 33416 33417 33416 33416 33417 33417 33417 33421 33434 33432
33450 33429 33427 33418 33418 33417 33426 33416 33416 33417 33417 33416 33432 33429 33436
33427 33429 33428 33417 33416 33416 33415 33417 33416 33417 33417 33417 33431 33432 33418
33428 33426 33426 33418 33418 33417 33416 33428 33416 33417 33417 33417 33429 33432 33424
33426 33427 33425 33416 33416 33416 33417 33417 33417 33417 33417 33417 33429 33432 33423
33433 33430 33426 33426 33418 33417 33417 33416 33416 33416 33416 33418 33423 33432 33423
33429 33429 33427 33427 33417 33417 33416 33417 33416 33416 33417 33417 33428 33432 33418
33427 33427 33426 33418 33417 33416 33416 33416 33427 33416 33417 33417 33429 33432 33421
33432 33428 33427 33428 33418 33416 33416 33416 33416 33417 33417 33417 33425 33432 33420
33425 33425 33428 33419 33417 33416 33416 33416 33416 33417 33417 33417 33432 33428 33422
33425 33425 33425 33414 33417 33417 33414 33416 33416 33417 33417 33417 33433 33432 33419
33428 33427 33424 33414 33418 33417 33416 33417 33416 33416 33416 33418 33432 33429 33426
33427 33432 33426 33414 33417 33417 33413 33430 33416 33428 33420 33417 33428 33428 33421
33427 33427 33424 33419 33417 33416 33416 33417 33416 33416 33416 33417 33428 33432 33423
33433 33429 33427 33418 33416 33416 33416 33416 33417 33417 33417 33417 33428 33428 33422
33428 33425 33425 33419 33423 33417 33417 33417 33416 33429 33417 33417 33429 33432 33422
33430 33425 33429 33417 33416 33416 33416 33416 33416 33416 33417 33417 33425 33431 33418
33432 33426 33426 33431 33418 33416 33415 33416 33417 33416 33417 33417 33417 33432 33418
33429 33431 33426 33426 33416 33417 33415 33417 33416 33417 33417 33417 33432 33432 33429
33432 33431 33429 33419 33416 33416 33416 33416 33416 33417 33416 33417 33425 33429 33425
33428 33429 33426 33414 33417 33416 33416 33430 33416 33420 33417 33417 33418 33432 33422

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 33422 bytes 100%
1,000 33415 bytes -7 bytes 100%
10,000 33414 bytes -1 byte 100%
100,000 33413 bytes -1 byte 2.61%
1,000,000
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
33497 bytes +84 bytes (+0.25%) +1 byte
33496 bytes +83 bytes (+0.25%)
33509 bytes +96 bytes (+0.29%) +13 bytes
33540 bytes +127 bytes (+0.38%) +44 bytes
33579 bytes +166 bytes (+0.50%) +83 bytes
33596 bytes +183 bytes (+0.55%) +100 bytes
33556 bytes +143 bytes (+0.43%) +60 bytes
33592 bytes +179 bytes (+0.54%) +96 bytes
33606 bytes +193 bytes (+0.58%) +110 bytes

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 24747 bytes -8666 bytes (-25.94%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 25879 bytes -7534 bytes (-22.55%)
Brotli (Wikipedia) brotli brotli -q 11 29574 bytes -3839 bytes (-11.49%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 29654 bytes -3759 bytes (-11.25%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 29664 bytes -3749 bytes (-11.22%)
LZMA2 (Wikipedia) xz xz -9 30796 bytes -2617 bytes (-7.83%)
ZSTD (Wikipedia) zstd zstd -19 31808 bytes -1605 bytes (-4.80%)

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