Choose a version:
12% The original file has 54742 bytes (53.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 6617 bytes (6.5k, 12%).

After GZIP compression these minified files vary in size:
Boot
  3007 bytes (2.9k)
CDN
gzip -6 (default)
  2839 bytes (2.8k)
local copy
gzip -9
  2839 bytes (2.8k)
local copy
cdnjs
  2821 bytes (2.8k)
CDN
jsdelivr
  2819 bytes (2.8k)
CDN
libdeflate -12
  2787 bytes (2.7k)
local copy
7zip -mx=9 -tgzip
  2786 bytes (2.7k)
local copy
pigz -11 -n
  2786 bytes (2.7k)
local copy
kzip -s0 -rn -b1
  2784 bytes (2.7k)
local copy
Zopfli
  2783 bytes (2.7k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.2.0.min.js

You will automatically get the smallest React 16.2.0 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 36 bytes by using my React 16.2.0 Zopfli version instead of the best available CDN (1.29% smaller than jsdelivr, 2783 vs. 2819 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 --mls16 --bsr7 --lazy --ohh

(found November 29, 2017)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 16  --mls16
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-16.2.0.min.js --location | md5sum
bca103da5b5404d93783ccf73e0e9d1e  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-16.2.0.min.zopfli.js.gz | md5sum
bca103da5b5404d93783ccf73e0e9d1e  -

SHA1:
curl --silent --compressed https://fb.me/react-16.2.0.min.js --location | sha1sum
643981b507e851701b0f8ef861a97a5442cde571  -
curl --silent --compressed http://minime.stephan-brumme.com/files/react/react-16.2.0.min.zopfli.js.gz | sha1sum
643981b507e851701b0f8ef861a97a5442cde571  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 3007 bytes bca103da5b5404d93783ccf73e0e9d1e December 5, 2017 @ 09:38
cdnjs 2821 bytes bca103da5b5404d93783ccf73e0e9d1e November 28, 2017 @ 23:03
jsdelivr 2819 bytes bca103da5b5404d93783ccf73e0e9d1e November 29, 2017 @ 15:38

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

Other Versions

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

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
2783 bytes -1 byte zopfli --i1000000 --mls16 --bsr7 --lazy --ohh November 29, 2017 @ 16:19
2784 bytes zopfli --i100 --mls16 --bsr13 --lazy --ohh November 29, 2017 @ 15:40

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

Most recent activity on December 5, 2017 @ 09:38.

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 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
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2783 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784
2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784 2784

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 2784 bytes 100%
1,000 2784 bytes 100%
10,000 2784 bytes 100%
100,000 2784 bytes 0.29%
1,000,000 2783 bytes -1 byte 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
2784 bytes +1 byte (+0.04%)
2784 bytes +1 byte (+0.04%)
2795 bytes +12 bytes (+0.43%) +11 bytes
2821 bytes +38 bytes (+1.37%) +37 bytes
2863 bytes +80 bytes (+2.87%) +79 bytes
2894 bytes +111 bytes (+3.99%) +110 bytes
2934 bytes +151 bytes (+5.43%) +150 bytes
2961 bytes +178 bytes (+6.40%) +177 bytes
2998 bytes +215 bytes (+7.73%) +214 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
Algorithm Program Parameters Size Compared To Best Zopfli
Brotli (Wikipedia) brotli brotli -q 11 2492 bytes -291 bytes (-10.46%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 2626 bytes -157 bytes (-5.64%)
ZSTD (Wikipedia) zstd zstd -19 2807 bytes +24 bytes (+0.86%)
LZMA2 (Wikipedia) xz xz -9 2860 bytes +77 bytes (+2.77%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 2951 bytes +168 bytes (+6.04%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 3009 bytes +226 bytes (+8.12%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 3516 bytes +733 bytes (+26.34%)

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 2017.
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