Choose a version:
12% The original file has 98230 bytes (95.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 11814 bytes (11.5k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4719 bytes (4.6k)
local copy
gzip -9
  4714 bytes (4.6k)
local copy
Boot
  4707 bytes (4.6k)
CDN
cdnjs
  4707 bytes (4.6k)
CDN
jsdelivr
  4699 bytes (4.6k)
CDN
7zip -mx=9 -tgzip
  4627 bytes (4.5k)
local copy
libdeflate -12
  4627 bytes (4.5k)
local copy
pigz -11 -n
  4627 bytes (4.5k)
local copy
kzip -s0 -rn -b1
  4625 bytes (4.5k)
local copy
Zopfli
  4622 bytes (4.5k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.6.3.min.js (or via HTTPS)

You will automatically get the smallest React 16.6.3 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 77 bytes by using my React 16.6.3 Zopfli version instead of the best available CDN (1.67% smaller than jsdelivr, 4622 vs. 4699 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 --mls4 --bsr7 --lazy --ohh

(found December 5, 2018)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 4  --mls4
block splitting recursion 7  --bsr7
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-16.6.3.min.js --location | md5sum
ef752361755a318f70b5a3ae9cb2ed3f  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.6.3.min.zopfli.js.gz | md5sum
ef752361755a318f70b5a3ae9cb2ed3f  -

SHA1:
curl --silent --compressed https://fb.me/react-16.6.3.min.js --location | sha1sum
11a5de229a48174c444df28d2a01f944fe803d78  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.6.3.min.zopfli.js.gz | sha1sum
11a5de229a48174c444df28d2a01f944fe803d78  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 4707 bytes ef752361755a318f70b5a3ae9cb2ed3f (invalid)
cdnjs 4707 bytes ef752361755a318f70b5a3ae9cb2ed3f (invalid)
jsdelivr 4699 bytes ef752361755a318f70b5a3ae9cb2ed3f December 5, 2018 @ 10:29

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

Other Versions

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

16.6.3, 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
4622 bytes -1 byte zopfli --i10000 --mls4 --bsr7 --lazy --ohh December 5, 2018 @ 10:39
4623 bytes -1 byte zopfli --i1000 --mls4 --bsr13 --lazy --ohh December 5, 2018 @ 10:34
4624 bytes zopfli --i100 --mls4 --bsr7 --lazy --ohh December 5, 2018 @ 10:31

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

Most recent activity on December 5, 2018 @ 13:50.

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
4630 4630 4631 4631 4631 4623 4631 4630 4623 4623 4623 4623 4626 4626 4626
4623 4623 4631 4631 4623 4623 4629 4629 4623 4623 4623 4623 4625 4625 4625
4623 4623 4623 4623 4623 4629 4635 4631 4623 4623 4623 4623 4629 4630 4630
4622 4622 4631 4631 4623 4623 4623 4631 4623 4623 4623 4623 4625 4629 4629
4631 4631 4631 4631 4631 4631 4635 4631 4623 4623 4623 4623 4626 4626 4626
4629 4629 4631 4631 4623 4623 4636 4623 4623 4623 4623 4623 4629 4629 4629
4623 4623 4631 4631 4631 4630 4632 4631 4623 4623 4623 4623 4629 4625 4625
4623 4623 4630 4631 4623 4630 4629 4623 4623 4623 4623 4623 4626 4629 4629
4631 4631 4631 4631 4623 4631 4631 4631 4623 4623 4623 4623 4625 4625 4625
4623 4623 4623 4623 4623 4623 4635 4628 4623 4623 4623 4623 4629 4629 4629
4629 4629 4629 4631 4631 4623 4636 4631 4623 4623 4623 4623 4625 4625 4625
4629 4629 4632 4631 4631 4632 4635 4631 4623 4623 4623 4623 4625 4629 4629
4629 4629 4630 4631 4631 4631 4628 4628 4623 4623 4623 4623 4625 4625 4625
4629 4629 4629 4631 4631 4631 4631 4632 4623 4623 4623 4623 4625 4625 4625
4624 4624 4623 4631 4623 4630 4629 4631 4623 4623 4623 4623 4624 4625 4625
4629 4629 4629 4631 4631 4623 4636 4629 4623 4623 4623 4623 4629 4629 4629
4624 4624 4630 4631 4631 4632 4628 4628 4623 4623 4623 4623 4625 4625 4625
4628 4628 4630 4631 4631 4631 4628 4631 4623 4623 4623 4623 4625 4625 4625
4628 4628 4629 4631 4631 4631 4635 4631 4623 4623 4623 4623 4624 4624 4624
4623 4623 4623 4631 4623 4623 4628 4631 4623 4623 4623 4623 4624 4624 4624
4630 4630 4629 4631 4623 4632 4629 4629 4623 4623 4623 4623 4630 4626 4626
4629 4629 4631 4629 4629 4629 4630 4631 4623 4623 4623 4623 4625 4625 4625
4629 4629 4629 4629 4629 4629 4635 4631 4623 4623 4623 4623 4624 4625 4625

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 4624 bytes 100%
1,000 4623 bytes -1 byte 100%
10,000 4622 bytes -1 byte 100%
100,000 4622 bytes 38.55%
1,000,000 4622 bytes 0.58%
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
4625 bytes +3 bytes (+0.06%)
4625 bytes +3 bytes (+0.06%)
4639 bytes +17 bytes (+0.37%) +14 bytes
4669 bytes +47 bytes (+1.02%) +44 bytes
4686 bytes +64 bytes (+1.38%) +61 bytes
4723 bytes +101 bytes (+2.19%) +98 bytes
4759 bytes +137 bytes (+2.96%) +134 bytes
4789 bytes +167 bytes (+3.61%) +164 bytes
4819 bytes +197 bytes (+4.26%) +194 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
Brotli (Wikipedia) brotli brotli -q 11 4144 bytes -478 bytes (-10.34%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4245 bytes -377 bytes (-8.16%)
Zstandard (Wikipedia) zstd zstd -19 4635 bytes +13 bytes (+0.28%)
LZMA2 (Wikipedia) xz xz -9 4664 bytes +42 bytes (+0.91%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4764 bytes +142 bytes (+3.07%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4796 bytes +174 bytes (+3.76%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5033 bytes +411 bytes (+8.89%)

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