Choose a version:
16% The original file has 142442 bytes (139.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 22631 bytes (22.1k, 16%).

After GZIP compression these minified files vary in size:
Boot
  8780 bytes (8.6k)
CDN
cdnjs
  7844 bytes (7.7k)
CDN
gzip -6 (default)
  7835 bytes (7.7k)
local copy
unpkg
  7814 bytes (7.6k)
CDN
gzip -9
  7808 bytes (7.6k)
local copy
libdeflate -12
  7627 bytes (7.4k)
local copy
7zip -mx=9 -tgzip
  7624 bytes (7.4k)
local copy
kzip -s0 -rn -b6
  7612 bytes (7.4k)
local copy
pigz -11 -n
  7516 bytes (7.3k)
local copy
Zopfli
  7501 bytes (7.3k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-15.6.0.min.js (or via HTTPS)

You will automatically get the smallest React 15.6.0 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 313 bytes by using my React 15.6.0 Zopfli version instead of the best available CDN (4.17% smaller than unpkg, 7501 vs. 7814 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 --mls128 --bsr11 --lazy --ohh

(found June 15, 2017)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 128  --mls128
block splitting recursion 11  --bsr11
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-15.6.0.min.js --location | md5sum
14b9cca6f002450560022fafb3677f9b  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-15.6.0.min.zopfli.js.gz | md5sum
14b9cca6f002450560022fafb3677f9b  -

SHA1:
curl --silent --compressed https://fb.me/react-15.6.0.min.js --location | sha1sum
e8c19708e17c0b671b2f1082bf631bb2e75c3184  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-15.6.0.min.zopfli.js.gz | sha1sum
e8c19708e17c0b671b2f1082bf631bb2e75c3184  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 8780 bytes 14b9cca6f002450560022fafb3677f9b (invalid)
cdnjs 7844 bytes 14b9cca6f002450560022fafb3677f9b (invalid)
unpkg 7814 bytes 14b9cca6f002450560022fafb3677f9b June 15, 2017 @ 14:19

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
7501 bytes -1 byte zopfli --i1000000 --mls128 --bsr11 --lazy --ohh June 15, 2017 @ 17:35
7502 bytes -1 byte zopfli --i100000 --mls128 --bsr11 --lazy --ohh June 15, 2017 @ 14:36
7503 bytes -1 byte zopfli --i10000 --mls128 --bsr11 --lazy --ohh June 15, 2017 @ 14:25
7504 bytes -2 bytes zopfli --i1000 --mls128 --bsr11 --lazy --ohh June 15, 2017 @ 14:23
7506 bytes zopfli --i100 --mls128 --bsr11 --lazy --ohh June 15, 2017 @ 14:21

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on June 16, 2017 @ 04:52.

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 10,000,000.
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
7552 7551 7552 7553 7555 7554 7554 7554 7613 7552 7613 7551 7550 7553 7553
7505 7509 7514 7510 7506 7520 7507 7509 7511 7528 7528 7518 7512 7517 7516
7519 7519 7523 7504 7505 7504 7510 7502 7526 7507 7503 7520 7505 7509 7510
7507 7507 7504 7509 7513 7512 7509 7514 7505 7507 7506 7508 7507 7505 7514
7504 7504 7509 7511 7505 7502 7539 7533 7502 7509 7510 7507 7508 7507 7506
7507 7507 7509 7509 7502 7502 7514 7509 7502 7507 7504 7507 7508 7505 7507
7507 7507 7509 7509 7504 7502 7502 7502 7504 7506 7502 7504 7508 7505 7508
7507 7507 7513 7509 7502 7507 7501 7505 7504 7512 7505 7507 7508 7505 7508
7506 7506 7505 7511 7505 7503 7502 7505 7502 7512 7506 7507 7515 7505 7507
7507 7507 7509 7507 7502 7509 7502 7502 7502 7512 7510 7502 7506 7519 7507
7504 7504 7509 7511 7506 7509 7504 7502 7502 7512 7505 7506 7508 7507 7507
7508 7508 7509 7510 7505 7509 7504 7505 7504 7509 7504 7504 7508 7513 7513
7507 7507 7509 7511 7502 7504 7504 7502 7502 7509 7504 7507 7508 7508 7508
7507 7507 7510 7509 7505 7504 7512 7506 7502 7509 7502 7504 7508 7505 7507
7507 7507 7509 7509 7504 7504 7502 7505 7504 7512 7502 7506 7515 7505 7507
7507 7507 7502 7509 7504 7503 7502 7505 7502 7506 7502 7504 7506 7507 7508
7507 7507 7509 7509 7504 7502 7502 7505 7504 7507 7502 7504 7506 7507 7509
7507 7507 7509 7502 7506 7503 7505 7506 7503 7508 7507 7507 7515 7505 7507
7509 7508 7505 7505 7506 7502 7505 7508 7505 7509 7537 7502 7507 7506 7508
7504 7504 7506 7509 7505 7505 7504 7507 7502 7508 7507 7503 7508 7507 7508
7507 7507 7504 7505 7502 7502 7504 7502 7502 7507 7502 7503 7508 7507 7508
7504 7504 7507 7504 7503 7509 7505 7502 7502 7512 7503 7502 7507 7508 7508
7508 7507 7509 7508 7502 7502 7505 7505 7506 7514 7504 7513 7507 7507 7507

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 7506 bytes 100%
1,000 7504 bytes -2 bytes 100%
10,000 7503 bytes -1 byte 100%
100,000 7502 bytes -1 byte 16.81%
1,000,000 7501 bytes -1 byte 0.29%
10,000,000 7501 bytes 0.29%

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
7620 bytes +119 bytes (+1.59%) +8 bytes
7620 bytes +119 bytes (+1.59%) +8 bytes
7619 bytes +118 bytes (+1.57%) +7 bytes
7652 bytes +151 bytes (+2.01%) +40 bytes
7676 bytes +175 bytes (+2.33%) +64 bytes
7673 bytes +172 bytes (+2.29%) +61 bytes
7612 bytes +111 bytes (+1.48%)
7647 bytes +146 bytes (+1.95%) +35 bytes
7664 bytes +163 bytes (+2.17%) +52 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
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 6871 bytes -630 bytes (-8.40%)
Brotli (Wikipedia) brotli brotli -q 11 6883 bytes -618 bytes (-8.24%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 7307 bytes -194 bytes (-2.59%)
LZMA2 (Wikipedia) xz xz -9 7428 bytes -73 bytes (-0.97%)
Zstandard (Wikipedia) zstd zstd -19 7560 bytes +59 bytes (+0.79%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 7594 bytes +93 bytes (+1.24%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7737 bytes +236 bytes (+3.15%)

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