Choose a version:
11% The original file has 87146 bytes (85.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 9766 bytes (9.5k, 11%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4073 bytes (4.0k)
local copy
gzip -9
  4070 bytes (4.0k)
local copy
jsdelivr
  4053 bytes (4.0k)
CDN
libdeflate -12
  3993 bytes (3.9k)
local copy
pigz -11 -n
  3991 bytes (3.9k)
local copy
7zip -mx=9 -tgzip
  3990 bytes (3.9k)
local copy
kzip -s0 -rn -b1
  3988 bytes (3.9k)
local copy
Zopfli
  3987 bytes (3.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.5.1.min.js (or via HTTPS)

You will automatically get the smallest React 16.5.1 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 66 bytes by using my React 16.5.1 Zopfli version instead of the best available CDN (1.66% smaller than jsdelivr, 3987 vs. 4053 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 --i1000 --mb8 --mls4096 --bsr8 --lazy --ohh

(found September 17, 2018)
Description Value Parameter
iterations 1000  --i1000
maximum blocks 8  --mb8
maximum length score 4096  --mls4096
block splitting recursion 8  --bsr8
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-16.5.1.min.js --location | md5sum
811529b009007135c0389cafe622e136  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.5.1.min.zopfli.js.gz | md5sum
811529b009007135c0389cafe622e136  -

SHA1:
curl --silent --compressed https://fb.me/react-16.5.1.min.js --location | sha1sum
7aee96fcf3f9b663fa5d1a50c5a28003cc8733b4  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.5.1.min.zopfli.js.gz | sha1sum
7aee96fcf3f9b663fa5d1a50c5a28003cc8733b4  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
jsdelivr 4053 bytes 811529b009007135c0389cafe622e136 September 17, 2018 @ 13:13

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
3987 bytes -2 bytes zopfli --i1000 --mls4096 --bsr8 --lazy --ohh September 17, 2018 @ 13:23
3989 bytes zopfli --i100 --mls4096 --bsr15 --lazy --ohh September 17, 2018 @ 13:21

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

Most recent activity on September 18, 2018 @ 01:25.

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
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3997 3997
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3991 3997 3997
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3993 3993 3993
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3992 3992
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3996 3996
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3995 3995
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3994
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3993 3993
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3997 3997
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3994 3994
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3992 3994 3994
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3992 3995 3995
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3992 3992 3992
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3994
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3994 3994
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3991 3992 3992
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3992 3992 3992
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3993 3993
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3994 3994
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3995 3995
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3993 3993 3993
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3994 3995 3995
3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3987 3992 3992

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 3989 bytes 100%
1,000 3987 bytes -2 bytes 100%
10,000 3987 bytes 100%
100,000 3987 bytes 82.32%
1,000,000 3987 bytes 0.29%
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
3988 bytes +1 byte (+0.03%)
3988 bytes +1 byte (+0.03%)
4007 bytes +20 bytes (+0.50%) +19 bytes
4032 bytes +45 bytes (+1.13%) +44 bytes
4065 bytes +78 bytes (+1.96%) +77 bytes
4093 bytes +106 bytes (+2.66%) +105 bytes
4128 bytes +141 bytes (+3.54%) +140 bytes
4167 bytes +180 bytes (+4.51%) +179 bytes
4203 bytes +216 bytes (+5.42%) +215 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 3569 bytes -418 bytes (-10.48%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 3698 bytes -289 bytes (-7.25%)
Zstandard (Wikipedia) zstd zstd -19 4017 bytes +30 bytes (+0.75%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4059 bytes +72 bytes (+1.81%)
LZMA2 (Wikipedia) xz xz -9 4068 bytes +81 bytes (+2.03%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4147 bytes +160 bytes (+4.01%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 4521 bytes +534 bytes (+13.39%)

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