Choose a version:
23% The original file has 571026 bytes (557.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 130289 bytes (127.2k, 23%).

After GZIP compression these minified files vary in size:
Boot
  43446 bytes (42.4k)
CDN, direct link
cdnjs
  36465 bytes (35.6k)
CDN, direct link
gzip -6 (default)
  35980 bytes (35.1k)
local copy
cdnhttps
  35960 bytes (35.1k)
CDN, direct link
unpkg
  35905 bytes (35.1k)
CDN, direct link
jsdelivr
  35822 bytes (35.0k)
CDN, direct link
gzip -9
  35796 bytes (35.0k)
local copy
7zip -mx=9 -tgzip
  34672 bytes (33.9k)
local copy
libdeflate -12
  34672 bytes (33.9k)
local copy
kzip -s0 -rn -b1
  34612 bytes (33.8k)
local copy
pigz -11 -n
  34556 bytes (33.7k)
local copy
Zopfli
  34545 bytes (33.7k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-0.12.1.min.js

You will automatically get the smallest React 0.12.1 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 1277 bytes by using my React 0.12.1 Zopfli version instead of the best available CDN (3.70% smaller than jsdelivr, 34545 vs. 35822 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 --i10000 --mb8 --mls64 --bsr12 --lazy --ohh

(found September 16, 2015)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 64  --mls64
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-0.12.1.min.js --location | md5sum
b261541e5b38172d02bad11c90d8f664  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.12.1.min.zopfli.js.gz | md5sum
b261541e5b38172d02bad11c90d8f664  -

SHA1:
curl --silent --compressed https://fb.me/react-0.12.1.min.js --location | sha1sum
67a57485f4c46a9d313c8c9132ae1cef606824bc  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-0.12.1.min.zopfli.js.gz | sha1sum
67a57485f4c46a9d313c8c9132ae1cef606824bc  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 43446 bytes b261541e5b38172d02bad11c90d8f664 March 20, 2015 @ 16:50
cdnjs 36465 bytes b261541e5b38172d02bad11c90d8f664 November 18, 2014 @ 15:00
cdnhttps 35960 bytes b261541e5b38172d02bad11c90d8f664 December 24, 2015 @ 07:35
unpkg 35905 bytes b261541e5b38172d02bad11c90d8f664 July 11, 2016 @ 15:34
jsdelivr 35822 bytes b261541e5b38172d02bad11c90d8f664 November 18, 2014 @ 10:27

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
34545 bytes -1 byte zopfli --i10000 --mls64 --bsr12 --lazy --ohh September 16, 2015 @ 03:47
34546 bytes -2 bytes zopfli --i1000 --mls64 --bsr12 --lazy --ohh September 14, 2015 @ 16:18
34548 bytes -1 byte zopfli --i1000 --mls64 --bsr10 --lazy --ohh September 14, 2015 @ 16:16
34549 bytes -4 bytes zopfli --i1000 --mls64 --bsr6 --lazy --ohh September 14, 2015 @ 16:14
34553 bytes zopfli --i100 --mls4096 --bsr7 --lazy --ohh September 14, 2015 @ 12:00

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
34560 34560 34562 34563 34562 34561 34560 34563 34567 34565 34564 34570 34564 34561 34564
34567 34566 34569 34569 34560 34557 34557 34557 34560 34561 34559 34567 34561 34561 34555
34548 34549 34548 34555 34547 34547 34547 34547 34547 34546 34548 34547 34548 34557 34548
34548 34549 34558 34559 34547 34547 34548 34549 34548 34545 34545 34545 34548 34558 34548
34547 34547 34557 34547 34547 34545 34547 34547 34547 34545 34551 34547 34548 34554 34548
34549 34548 34556 34558 34547 34547 34549 34547 34547 34547 34545 34545 34547 34547 34548
34549 34547 34554 34560 34547 34547 34547 34548 34547 34547 34545 34549 34552 34548 34550
34547 34547 34558 34558 34549 34547 34548 34547 34547 34545 34548 34547 34548 34549 34561
34548 34549 34559 34548 34547 34545 34549 34549 34547 34547 34547 34547 34548 34549 34546
34547 34547 34558 34558 34547 34549 34548 34547 34547 34545 34551 34547 34548 34549 34546
34547 34547 34557 34558 34547 34548 34547 34547 34547 34547 34549 34547 34550 34549 34548
34551 34551 34557 34558 34547 34547 34548 34547 34547 34545 34545 34547 34548 34549 34548
34551 34551 34556 34558 34547 34549 34547 34547 34547 34545 34551 34547 34548 34549 34548
34549 34551 34557 34558 34547 34547 34547 34547 34547 34545 34552 34547 34547 34555 34548
34552 34552 34557 34558 34547 34545 34548 34547 34549 34546 34553 34547 34549 34558 34548
34549 34548 34558 34547 34547 34547 34548 34547 34547 34545 34553 34547 34549 34558 34546
34549 34552 34560 34560 34549 34549 34547 34547 34547 34547 34548 34547 34548 34557 34548
34548 34547 34555 34560 34547 34547 34548 34547 34547 34547 34548 34547 34548 34549 34548
34552 34549 34558 34559 34549 34549 34549 34547 34547 34545 34549 34547 34549 34549 34548
34556 34548 34557 34558 34548 34549 34547 34547 34550 34555 34552 34547 34548 34557 34548
34549 34548 34558 34547 34547 34547 34548 34547 34547 34547 34549 34547 34547 34548 34547
34547 34548 34558 34561 34547 34547 34547 34547 34547 34547 34553 34547 34547 34559 34548
34548 34548 34557 34558 34549 34549 34548 34547 34547 34555 34552 34547 34549 34558 34548

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 34553 bytes 100%
1,000 34546 bytes -7 bytes 100%
10,000 34545 bytes -1 byte 100%
100,000 34545 bytes 6.67%
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
34617 bytes +72 bytes (+0.21%) +5 bytes
34612 bytes +67 bytes (+0.19%)
34632 bytes +87 bytes (+0.25%) +20 bytes
34655 bytes +110 bytes (+0.32%) +43 bytes
34693 bytes +148 bytes (+0.43%) +81 bytes
34714 bytes +169 bytes (+0.49%) +102 bytes
34756 bytes +211 bytes (+0.61%) +144 bytes
34768 bytes +223 bytes (+0.65%) +156 bytes
34772 bytes +227 bytes (+0.66%) +160 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 25519 bytes -9026 bytes (-26.13%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 26781 bytes -7764 bytes (-22.48%)
Brotli (Wikipedia) brotli brotli -q 11 30541 bytes -4004 bytes (-11.59%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 30646 bytes -3899 bytes (-11.29%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 30868 bytes -3677 bytes (-10.64%)
LZMA2 (Wikipedia) xz xz -9 31764 bytes -2781 bytes (-8.05%)
ZSTD (Wikipedia) zstd zstd -19 32770 bytes -1775 bytes (-5.14%)

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