Choose a version:
12% The original file has 59086 bytes (57.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 7217 bytes (7.0k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  3070 bytes (3.0k)
local copy
gzip -9
  3070 bytes (3.0k)
local copy
cdnjs
  3053 bytes (3.0k)
CDN
jsdelivr
  3050 bytes (3.0k)
CDN
libdeflate -12
  3011 bytes (2.9k)
local copy
pigz -11 -n
  3011 bytes (2.9k)
local copy
kzip -s0 -rn -b0
  3010 bytes (2.9k)
local copy
7zip -mx=9 -tgzip
  3008 bytes (2.9k)
local copy
Zopfli
  3007 bytes (2.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.4.2.min.js (or via HTTPS)

You will automatically get the smallest React 16.4.2 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 43 bytes by using my React 16.4.2 Zopfli version instead of the best available CDN (1.43% smaller than jsdelivr, 3007 vs. 3050 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 --mls256 --bsr2 --lazy --ohh

(found August 3, 2018)
Description Value Parameter
iterations 1000  --i1000
maximum blocks 8  --mb8
maximum length score 256  --mls256
block splitting recursion 2  --bsr2
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-16.4.2.min.js --location | md5sum
c485b1a84875e690cb252ffbab97809b  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.4.2.min.zopfli.js.gz | md5sum
c485b1a84875e690cb252ffbab97809b  -

SHA1:
curl --silent --compressed https://fb.me/react-16.4.2.min.js --location | sha1sum
927e7190e1df836c65bf6c9b3f4ba4a2b40b9aee  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.4.2.min.zopfli.js.gz | sha1sum
927e7190e1df836c65bf6c9b3f4ba4a2b40b9aee  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
cdnjs 3053 bytes c485b1a84875e690cb252ffbab97809b (invalid)
jsdelivr 3050 bytes c485b1a84875e690cb252ffbab97809b August 3, 2018 @ 14:43

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

Other Versions

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

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
3007 bytes -1 byte zopfli --i1000 --mls256 --bsr2 --lazy --ohh August 3, 2018 @ 15:07
3008 bytes zopfli --i100 --mls512 --bsr15 --lazy --ohh August 3, 2018 @ 14:49

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

Most recent activity on August 4, 2018 @ 04:29.

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:
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
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007
3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007 3007

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 3008 bytes 100%
1,000 3007 bytes -1 byte 100%
10,000 3007 bytes 100%
100,000 3007 bytes 100%
1,000,000 3007 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
3010 bytes +3 bytes (+0.10%)
3010 bytes +3 bytes (+0.10%)
3024 bytes +17 bytes (+0.57%) +14 bytes
3044 bytes +37 bytes (+1.23%) +34 bytes
3077 bytes +70 bytes (+2.33%) +67 bytes
3104 bytes +97 bytes (+3.23%) +94 bytes
3148 bytes +141 bytes (+4.69%) +138 bytes
3186 bytes +179 bytes (+5.95%) +176 bytes
3223 bytes +216 bytes (+7.18%) +213 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 2665 bytes -342 bytes (-11.37%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 2812 bytes -195 bytes (-6.48%)
Zstandard (Wikipedia) zstd zstd -19 3039 bytes +32 bytes (+1.06%)
LZMA2 (Wikipedia) xz xz -9 3088 bytes +81 bytes (+2.69%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 3163 bytes +156 bytes (+5.19%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 3293 bytes +286 bytes (+9.51%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 3686 bytes +679 bytes (+22.58%)

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