Choose a version:
21% The original file has 703233 bytes (686.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 148583 bytes (145.1k, 21%).

After GZIP compression these minified files vary in size:
Boot
  51949 bytes (50.7k)
CDN
cdnjs
  44689 bytes (43.6k)
CDN
cdnhttps
  44271 bytes (43.2k)
CDN
unpkg
  44271 bytes (43.2k)
CDN
gzip -6 (default)
  44254 bytes (43.2k)
local copy
jsdelivr
  44173 bytes (43.1k)
CDN
gzip -9
  44082 bytes (43.0k)
local copy
7zip -mx=9 -tgzip
  42640 bytes (41.6k)
local copy
libdeflate -12
  42622 bytes (41.6k)
local copy
kzip -s0 -rn -b7
  42540 bytes (41.5k)
local copy
pigz -11 -n
  42517 bytes (41.5k)
local copy
Zopfli
  42361 bytes (41.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-15.3.0.min.js (or via HTTPS)

You will automatically get the smallest React 15.3.0 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 1812 bytes by using my React 15.3.0 Zopfli version instead of the best available CDN (4.28% smaller than jsdelivr, 42361 vs. 44173 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 --mls64 --bsr16 --lazy --ohh

(found July 30, 2016)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 64  --mls64
block splitting recursion 16  --bsr16
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-15.3.0.min.js --location | md5sum
8d7194c5afc8581bd892ccfa038e8da7  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-15.3.0.min.zopfli.js.gz | md5sum
8d7194c5afc8581bd892ccfa038e8da7  -

SHA1:
curl --silent --compressed https://fb.me/react-15.3.0.min.js --location | sha1sum
cbc5e6ddcbb2c8443e19a02d21f40f1538acd193  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-15.3.0.min.zopfli.js.gz | sha1sum
cbc5e6ddcbb2c8443e19a02d21f40f1538acd193  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 51949 bytes 8d7194c5afc8581bd892ccfa038e8da7 August 2, 2016 @ 07:51
cdnjs 44689 bytes 8d7194c5afc8581bd892ccfa038e8da7 August 1, 2016 @ 19:46
cdnhttps 44271 bytes 8d7194c5afc8581bd892ccfa038e8da7 November 22, 2016 @ 16:40
unpkg 44271 bytes 8d7194c5afc8581bd892ccfa038e8da7 July 29, 2016 @ 23:29
jsdelivr 44173 bytes 8d7194c5afc8581bd892ccfa038e8da7 August 1, 2016 @ 19:35

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
42361 bytes -1 byte zopfli --i1000000 --mls64 --bsr16 --lazy --ohh July 30, 2016 @ 21:37
42362 bytes -1 byte zopfli --i1000000 --mls64 --bsr11 --lazy --ohh July 30, 2016 @ 15:29
42363 bytes -4 bytes zopfli --i1000000 --mls16 --bsr17 --lazy --ohh July 30, 2016 @ 09:13
42367 bytes -4 bytes zopfli --i100000 --mls16 --bsr17 --lazy --ohh July 30, 2016 @ 00:47
42371 bytes -1 byte zopfli --i10000 --mls64 --bsr11 --lazy --ohh July 29, 2016 @ 23:53
42372 bytes -6 bytes zopfli --i10000 --mls16 --bsr17 --lazy --ohh July 29, 2016 @ 23:43
42378 bytes -1 byte zopfli --i1000 --mls16 --bsr17 --lazy --ohh July 29, 2016 @ 23:37
42379 bytes -11 bytes zopfli --i1000 --mls64 --bsr11 --lazy --ohh July 29, 2016 @ 23:37
42390 bytes zopfli --i100 --mls16 --bsr17 --lazy --ohh July 29, 2016 @ 23:33

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

Most recent activity on November 22, 2016 @ 16:40.

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
42490 42493 42493 42434 42457 42463 42572 42569 42571 42502 42661 42661 42586 42579 42590
42411 42409 42411 42578 42400 42393 42476 42482 42476 42478 42478 42571 42578 42586 42579
42390 42391 42572 42474 42478 42574 42480 42579 42576 42577 42571 42572 42580 42586 42584
42403 42389 42391 42408 42387 42414 42382 42393 42572 42571 42574 42570 42581 42584 42579
42383 42409 42389 42413 42384 42384 42384 42392 42380 42380 42382 42572 42580 42581 42578
42378 42382 42384 42382 42379 42475 42486 42502 42481 42476 42574 42573 42578 42574 42580
42474 42469 42474 42482 42475 42472 42471 42479 42468 42473 42572 42572 42582 42577 42578
42389 42472 42473 42484 42383 42362 42573 42572 42388 42385 42384 42573 42583 42577 42577
42390 42388 42390 42478 42477 42383 42390 42476 42473 42382 42475 42574 42578 42584 42580
42383 42380 42389 42405 42387 42382 42383 42474 42380 42383 42389 42572 42579 42586 42579
42390 42387 42389 42481 42380 42380 42385 42392 42475 42381 42473 42571 42579 42578 42579
42393 42469 42385 42485 42395 42381 42473 42482 42472 42386 42385 42574 42584 42575 42578
42473 42469 42479 42479 42379 42361 42386 42474 42473 42393 42385 42572 42579 42578 42577
42381 42398 42388 42363 42384 42383 42472 42574 42379 42472 42388 42573 42578 42578 42578
42389 42386 42394 42395 42388 42371 42476 42572 42385 42387 42387 42573 42580 42578 42579
42390 42473 42393 42486 42389 42383 42379 42392 42383 42385 42572 42570 42579 42573 42577
42476 42473 42482 42484 42381 42473 42473 42474 42474 42475 42471 42574 42579 42574 42577
42393 42476 42385 42395 42474 42369 42476 42475 42388 42385 42387 42570 42580 42578 42579
42389 42388 42389 42395 42386 42381 42469 42476 42474 42473 42468 42571 42581 42574 42579
42383 42479 42387 42395 42477 42476 42470 42475 42471 42477 42387 42571 42580 42578 42579
42388 42478 42476 42398 42475 42380 42474 42473 42474 42382 42469 42571 42579 42581 42579
42390 42387 42481 42394 42473 42384 42382 42384 42480 42385 42382 42571 42580 42580 42579
42385 42388 42390 42396 42384 42383 42389 42473 42387 42476 42390 42572 42578 42580 42579

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 42390 bytes 100%
1,000 42378 bytes -12 bytes 100%
10,000 42371 bytes -7 bytes 100%
100,000 42365 bytes -6 bytes 1.45%
1,000,000 42361 bytes -4 bytes 0.87%
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
42669 bytes +308 bytes (+0.73%) +129 bytes
42673 bytes +312 bytes (+0.74%) +133 bytes
42676 bytes +315 bytes (+0.74%) +136 bytes
42602 bytes +241 bytes (+0.57%) +62 bytes
42569 bytes +208 bytes (+0.49%) +29 bytes
42569 bytes +208 bytes (+0.49%) +29 bytes
42562 bytes +201 bytes (+0.47%) +22 bytes
42540 bytes +179 bytes (+0.42%)
42582 bytes +221 bytes (+0.52%) +42 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
ZPAQ (Wikipedia) zpaq zpaq -method 69 30980 bytes -11381 bytes (-26.87%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 33533 bytes -8828 bytes (-20.84%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 35615 bytes -6746 bytes (-15.93%)
Brotli (Wikipedia) brotli brotli -q 11 37293 bytes -5068 bytes (-11.96%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 37892 bytes -4469 bytes (-10.55%)
LZMA2 (Wikipedia) xz xz -9 38544 bytes -3817 bytes (-9.01%)
Zstandard (Wikipedia) zstd zstd -19 40235 bytes -2126 bytes (-5.02%)

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