Choose a version:
12% The original file has 85735 bytes (83.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 10402 bytes (10.2k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4255 bytes (4.2k)
local copy
gzip -9
  4251 bytes (4.2k)
local copy
jsdelivr
  4235 bytes (4.1k)
CDN
libdeflate -12
  4176 bytes (4.1k)
local copy
7zip -mx=9 -tgzip
  4174 bytes (4.1k)
local copy
kzip -s0 -rn -b1
  4171 bytes (4.1k)
local copy
pigz -11 -n
  4171 bytes (4.1k)
local copy
Zopfli
  4169 bytes (4.1k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.5.2.min.js (or via HTTPS)

You will automatically get the smallest React 16.5.2 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 66 bytes by using my React 16.5.2 Zopfli version instead of the best available CDN (1.58% smaller than jsdelivr, 4169 vs. 4235 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 --mls2 --bsr4 --lazy --ohh

(found September 20, 2018)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 2  --mls2
block splitting recursion 4  --bsr4
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-16.5.2.min.js --location | md5sum
e370fa665bd29f9a4adb1702a753bfff  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.5.2.min.zopfli.js.gz | md5sum
e370fa665bd29f9a4adb1702a753bfff  -

SHA1:
curl --silent --compressed https://fb.me/react-16.5.2.min.js --location | sha1sum
cd34d33cd10eca240199f8ee71b45aa51eb7231c  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.5.2.min.zopfli.js.gz | sha1sum
cd34d33cd10eca240199f8ee71b45aa51eb7231c  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
jsdelivr 4235 bytes e370fa665bd29f9a4adb1702a753bfff September 20, 2018 @ 10:10

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
4169 bytes -1 byte zopfli --i100000 --mls2 --bsr4 --lazy --ohh September 20, 2018 @ 10:25
4170 bytes -1 byte zopfli --i1000 --mls2 --bsr4 --lazy --ohh September 20, 2018 @ 10:14
4171 bytes zopfli --i100 --mls64 --bsr15 --lazy --ohh September 20, 2018 @ 10:12

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

Most recent activity on September 20, 2018 @ 15:38.

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
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4173 4173
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4174 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4176 4176
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4173 4173
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4174 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4176 4173 4173
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4176 4176 4176
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4176 4176 4176
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4174 4174 4174
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4176 4176 4176
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4176 4176 4176
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4175 4175 4175
4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4169 4176 4176 4176

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 4171 bytes 100%
1,000 4170 bytes -1 byte 100%
10,000 4170 bytes 100%
100,000 4169 bytes -1 byte 81.16%
1,000,000 4169 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
4172 bytes +3 bytes (+0.07%) +1 byte
4171 bytes +2 bytes (+0.05%)
4189 bytes +20 bytes (+0.48%) +18 bytes
4222 bytes +53 bytes (+1.27%) +51 bytes
4245 bytes +76 bytes (+1.82%) +74 bytes
4278 bytes +109 bytes (+2.61%) +107 bytes
4302 bytes +133 bytes (+3.19%) +131 bytes
4339 bytes +170 bytes (+4.08%) +168 bytes
4371 bytes +202 bytes (+4.85%) +200 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 3731 bytes -438 bytes (-10.51%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 3852 bytes -317 bytes (-7.60%)
Zstandard (Wikipedia) zstd zstd -19 4203 bytes +34 bytes (+0.82%)
LZMA2 (Wikipedia) xz xz -9 4244 bytes +75 bytes (+1.80%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4288 bytes +119 bytes (+2.85%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4360 bytes +191 bytes (+4.58%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 4674 bytes +505 bytes (+12.11%)

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