Choose a version:
13% The original file has 56545 bytes (55.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 7164 bytes (7.0k, 13%).

After GZIP compression these minified files vary in size:
Boot
  3243 bytes (3.2k)
CDN
gzip -6 (default)
  3060 bytes (3.0k)
local copy
gzip -9
  3059 bytes (3.0k)
local copy
cdnjs
  3049 bytes (3.0k)
CDN
jsdelivr
  3040 bytes (3.0k)
CDN
7zip -mx=9 -tgzip
  3004 bytes (2.9k)
local copy
pigz -11 -n
  3003 bytes (2.9k)
local copy
libdeflate -12
  3001 bytes (2.9k)
local copy
kzip -s0 -rn -b1
  3000 bytes (2.9k)
local copy
Zopfli
  3000 bytes (2.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.3.2.min.js (or via HTTPS)

You will automatically get the smallest React 16.3.2 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 40 bytes by using my React 16.3.2 Zopfli version instead of the best available CDN (1.33% smaller than jsdelivr, 3000 vs. 3040 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 --i100 --mb8 --mls4 --bsr21 --lazy --ohh

(found April 24, 2018)
Description Value Parameter
iterations 100  --i100
maximum blocks 8  --mb8
maximum length score 4  --mls4
block splitting recursion 21  --bsr21
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-16.3.2.min.js --location | md5sum
cdf9611df0cc6d0a0db5de1af4cf4697  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.3.2.min.zopfli.js.gz | md5sum
cdf9611df0cc6d0a0db5de1af4cf4697  -

SHA1:
curl --silent --compressed https://fb.me/react-16.3.2.min.js --location | sha1sum
0500803a819aa37ee24049ffb3a89445cda06c7b  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.3.2.min.zopfli.js.gz | sha1sum
0500803a819aa37ee24049ffb3a89445cda06c7b  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 3243 bytes cdf9611df0cc6d0a0db5de1af4cf4697 April 18, 2018 @ 03:42
cdnjs 3049 bytes cdf9611df0cc6d0a0db5de1af4cf4697 April 16, 2018 @ 18:57
jsdelivr 3040 bytes cdf9611df0cc6d0a0db5de1af4cf4697 April 24, 2018 @ 11:56

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
3000 bytes zopfli --i100 --mls4 --bsr21 --lazy --ohh April 24, 2018 @ 11:59

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

Most recent activity on April 24, 2018 @ 15:33.

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 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
3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000
3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000
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3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000
3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000
3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000
3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000
3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000 3000

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 3000 bytes 100%
1,000 3000 bytes 100%
10,000 3000 bytes 100%
100,000 3000 bytes 0.29%
1,000,000 3000 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
3000 bytes – (0.00%)
3000 bytes – (0.00%)
3015 bytes +15 bytes (+0.50%) +15 bytes
3036 bytes +36 bytes (+1.20%) +36 bytes
3071 bytes +71 bytes (+2.37%) +71 bytes
3099 bytes +99 bytes (+3.30%) +99 bytes
3145 bytes +145 bytes (+4.83%) +145 bytes
3183 bytes +183 bytes (+6.10%) +183 bytes
3221 bytes +221 bytes (+7.37%) +221 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 2662 bytes -338 bytes (-11.27%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 2802 bytes -198 bytes (-6.60%)
Zstandard (Wikipedia) zstd zstd -19 3035 bytes +35 bytes (+1.17%)
LZMA2 (Wikipedia) xz xz -9 3084 bytes +84 bytes (+2.80%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 3157 bytes +157 bytes (+5.23%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 3280 bytes +280 bytes (+9.33%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 3674 bytes +674 bytes (+22.47%)

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