Choose a version:
12% The original file has 56109 bytes (54.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 6868 bytes (6.7k, 12%).

After GZIP compression these minified files vary in size:
Boot
  3138 bytes (3.1k)
CDN
gzip -6 (default)
  2963 bytes (2.9k)
local copy
gzip -9
  2963 bytes (2.9k)
local copy
cdnjs
  2956 bytes (2.9k)
CDN
jsdelivr
  2943 bytes (2.9k)
CDN
7zip -mx=9 -tgzip
  2910 bytes (2.8k)
local copy
libdeflate -12
  2910 bytes (2.8k)
local copy
kzip -s0 -rn -b1
  2909 bytes (2.8k)
local copy
pigz -11 -n
  2909 bytes (2.8k)
local copy
Zopfli
  2906 bytes (2.8k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.3.1.min.js (or via HTTPS)

You will automatically get the smallest React 16.3.1 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 37 bytes by using my React 16.3.1 Zopfli version instead of the best available CDN (1.27% smaller than jsdelivr, 2906 vs. 2943 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 --mls8192 --bsr2 --lazy --ohh

(found April 23, 2018)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 8192  --mls8192
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-16.3.1.min.js --location | md5sum
2fe5eb7f26bb33870560d371cb8b9161  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.3.1.min.zopfli.js.gz | md5sum
2fe5eb7f26bb33870560d371cb8b9161  -

SHA1:
curl --silent --compressed https://fb.me/react-16.3.1.min.js --location | sha1sum
eaf16b78510b180560ecefcb945e0cf2b97b6978  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.3.1.min.zopfli.js.gz | sha1sum
eaf16b78510b180560ecefcb945e0cf2b97b6978  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 3138 bytes 2fe5eb7f26bb33870560d371cb8b9161 April 4, 2018 @ 06:37
cdnjs 2956 bytes 2fe5eb7f26bb33870560d371cb8b9161 April 4, 2018 @ 03:46
jsdelivr 2943 bytes 2fe5eb7f26bb33870560d371cb8b9161 April 23, 2018 @ 08:57

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
2906 bytes -1 byte zopfli --i1000000 --mls8192 --bsr2 --lazy --ohh April 23, 2018 @ 20:33
2907 bytes -1 byte zopfli --i10000 --mls8192 --bsr2 --lazy --ohh April 23, 2018 @ 12:22
2908 bytes -1 byte zopfli --i1000 --mls512 --bsr4 --lazy --ohh April 23, 2018 @ 10:02
2909 bytes zopfli --i100 --mls32768 --bsr6 --lazy --ohh April 23, 2018 @ 09:06

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 @ 00:55.

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 10,000,000.
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
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2906 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907
2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2908 2907 2907 2907

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 2909 bytes 100%
1,000 2908 bytes -1 byte 100%
10,000 2907 bytes -1 byte 100%
100,000 2907 bytes 20.00%
1,000,000 2906 bytes -1 byte 0.29%
10,000,000 2906 bytes 0.29%

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
2909 bytes +3 bytes (+0.10%)
2909 bytes +3 bytes (+0.10%)
2918 bytes +12 bytes (+0.41%) +9 bytes
2944 bytes +38 bytes (+1.31%) +35 bytes
2974 bytes +68 bytes (+2.34%) +65 bytes
3002 bytes +96 bytes (+3.30%) +93 bytes
3038 bytes +132 bytes (+4.54%) +129 bytes
3079 bytes +173 bytes (+5.95%) +170 bytes
3116 bytes +210 bytes (+7.23%) +207 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 2589 bytes -317 bytes (-10.91%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 2717 bytes -189 bytes (-6.50%)
Zstandard (Wikipedia) zstd zstd -19 2939 bytes +33 bytes (+1.14%)
LZMA2 (Wikipedia) xz xz -9 2988 bytes +82 bytes (+2.82%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 3040 bytes +134 bytes (+4.61%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 3127 bytes +221 bytes (+7.60%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 3598 bytes +692 bytes (+23.81%)

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