Choose a version:
16% The original file has 141859 bytes (138.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 22918 bytes (22.4k, 16%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  7905 bytes (7.7k)
local copy
unpkg
  7891 bytes (7.7k)
CDN
gzip -9
  7882 bytes (7.7k)
local copy
7zip -mx=9 -tgzip
  7694 bytes (7.5k)
local copy
libdeflate -12
  7691 bytes (7.5k)
local copy
kzip -s0 -rn -b6
  7684 bytes (7.5k)
local copy
pigz -11 -n
  7585 bytes (7.4k)
local copy
Zopfli
  7572 bytes (7.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-15.6.2.min.js (or via HTTPS)

You will automatically get the smallest React 15.6.2 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 319 bytes by using my React 15.6.2 Zopfli version instead of the best available CDN (4.21% smaller than unpkg, 7572 vs. 7891 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 --mls32 --bsr25 --lazy --ohh

(found September 27, 2017)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 32  --mls32
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

Verify file integrity

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

MD5:
curl --silent --compressed https://fb.me/react-15.6.2.min.js --location | md5sum
182301dc5d717c4f828b5665ac6bfa3a  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-15.6.2.min.zopfli.js.gz | md5sum
182301dc5d717c4f828b5665ac6bfa3a  -

SHA1:
curl --silent --compressed https://fb.me/react-15.6.2.min.js --location | sha1sum
3fcf6121e7f647b59e314ec92d23e093a4c3b303  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-15.6.2.min.zopfli.js.gz | sha1sum
3fcf6121e7f647b59e314ec92d23e093a4c3b303  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 7891 bytes 182301dc5d717c4f828b5665ac6bfa3a September 26, 2017 @ 02:09

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

Other Versions

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

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
7572 bytes -1 byte zopfli --i100000 --mls32 --bsr25 --lazy --ohh September 27, 2017 @ 16:15
7573 bytes -1 byte zopfli --i100000 --mls32 --bsr20 --lazy --ohh September 27, 2017 @ 15:58
7574 bytes -1 byte zopfli --i10000 --mls32 --bsr20 --lazy --ohh September 27, 2017 @ 15:06
7575 bytes -2 bytes zopfli --i1000 --mls128 --bsr20 --lazy --ohh September 27, 2017 @ 14:39
7577 bytes zopfli --i100 --mls512 --bsr15 --lazy --ohh September 27, 2017 @ 14:03

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

Most recent activity on September 28, 2017 @ 15:09.

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
7599 7600 7624 7594 7591 7593 7593 7592 7593 7596 7685 7613 7626 7622 7622
7593 7590 7584 7583 7581 7584 7581 7582 7583 7578 7577 7587 7588 7600 7573
7587 7587 7581 7580 7575 7576 7576 7573 7573 7576 7573 7575 7578 7579 7573
7580 7580 7575 7580 7575 7582 7574 7583 7584 7580 7576 7578 7578 7580 7580
7580 7580 7578 7580 7572 7576 7576 7576 7576 7582 7575 7577 7577 7579 7575
7590 7590 7585 7586 7578 7578 7573 7582 7577 7576 7579 7575 7575 7579 7578
7587 7587 7578 7580 7575 7578 7575 7575 7576 7576 7573 7578 7578 7580 7580
7583 7583 7578 7582 7575 7576 7576 7578 7573 7578 7582 7576 7574 7580 7581
7581 7580 7573 7580 7573 7576 7576 7577 7576 7578 7575 7576 7576 7579 7576
7580 7580 7578 7580 7572 7576 7576 7573 7573 7578 7578 7578 7576 7580 7576
7586 7586 7578 7580 7573 7578 7574 7576 7576 7580 7575 7577 7578 7579 7575
7582 7582 7579 7583 7573 7577 7577 7576 7573 7576 7575 7578 7576 7579 7575
7583 7583 7578 7581 7576 7576 7576 7576 7573 7576 7575 7578 7578 7579 7575
7580 7580 7580 7581 7573 7576 7576 7575 7576 7576 7573 7578 7578 7580 7575
7585 7585 7578 7580 7573 7576 7576 7576 7573 7576 7575 7578 7578 7579 7578
7582 7582 7578 7581 7573 7578 7576 7575 7577 7577 7573 7578 7579 7580 7580
7580 7580 7580 7582 7573 7578 7573 7575 7573 7578 7575 7578 7573 7580 7580
7580 7580 7576 7577 7576 7579 7578 7573 7577 7577 7575 7575 7576 7579 7579
7582 7582 7580 7578 7572 7577 7576 7576 7575 7579 7576 7576 7578 7577 7578
7578 7578 7577 7573 7576 7577 7582 7575 7576 7578 7604 7576 7577 7577 7578
7582 7582 7575 7578 7572 7577 7576 7575 7573 7605 7601 7578 7576 7578 7580
7583 7582 7579 7582 7573 7576 7577 7576 7577 7576 7573 7576 7573 7579 7576
7580 7580 7579 7582 7573 7576 7577 7576 7577 7580 7577 7576 7577 7580 7577

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 7577 bytes 100%
1,000 7575 bytes -2 bytes 100%
10,000 7574 bytes -1 byte 100%
100,000 7572 bytes -2 bytes 11.59%
1,000,000 7572 bytes 1.16%
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
7689 bytes +117 bytes (+1.55%) +5 bytes
7689 bytes +117 bytes (+1.55%) +5 bytes
7690 bytes +118 bytes (+1.56%) +6 bytes
7723 bytes +151 bytes (+1.99%) +39 bytes
7747 bytes +175 bytes (+2.31%) +63 bytes
7754 bytes +182 bytes (+2.40%) +70 bytes
7684 bytes +112 bytes (+1.48%)
7721 bytes +149 bytes (+1.97%) +37 bytes
7760 bytes +188 bytes (+2.48%) +76 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 6932 bytes -640 bytes (-8.45%)
Brotli (Wikipedia) brotli brotli -q 11 6949 bytes -623 bytes (-8.23%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 7369 bytes -203 bytes (-2.68%)
LZMA2 (Wikipedia) xz xz -9 7504 bytes -68 bytes (-0.90%)
Zstandard (Wikipedia) zstd zstd -19 7634 bytes +62 bytes (+0.82%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 7647 bytes +75 bytes (+0.99%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7802 bytes +230 bytes (+3.04%)

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