Choose a version:
12% The original file has 101072 bytes (98.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12407 bytes (12.1k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4825 bytes (4.7k)
local copy
gzip -9
  4821 bytes (4.7k)
local copy
Boot
  4813 bytes (4.7k)
CDN
cdnjs
  4813 bytes (4.7k)
CDN
jsdelivr
  4805 bytes (4.7k)
CDN
libdeflate -12
  4730 bytes (4.6k)
local copy
pigz -11 -n
  4729 bytes (4.6k)
local copy
7zip -mx=9 -tgzip
  4728 bytes (4.6k)
local copy
kzip -s0 -rn -b1
  4728 bytes (4.6k)
local copy
Zopfli
  4724 bytes (4.6k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.8.1.min.js (or via HTTPS)

You will automatically get the smallest React 16.8.1 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 81 bytes by using my React 16.8.1 Zopfli version instead of the best available CDN (1.71% smaller than jsdelivr, 4724 vs. 4805 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 --mls8192 --bsr23 --lazy --ohh

(found August 7, 2019)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 8192  --mls8192
block splitting recursion 23  --bsr23
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-16.8.1.min.js --location | md5sum
648b52e105850db91ae2bebe20548455  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.8.1.min.zopfli.js.gz | md5sum
648b52e105850db91ae2bebe20548455  -

SHA1:
curl --silent --compressed https://fb.me/react-16.8.1.min.js --location | sha1sum
113a97dffe45314ea70f7f7d3875ae7b45301ce3  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.8.1.min.zopfli.js.gz | sha1sum
113a97dffe45314ea70f7f7d3875ae7b45301ce3  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 4813 bytes 648b52e105850db91ae2bebe20548455 February 6, 2019 @ 19:45
cdnjs 4813 bytes 648b52e105850db91ae2bebe20548455 February 6, 2019 @ 19:45
jsdelivr 4805 bytes 648b52e105850db91ae2bebe20548455 August 7, 2019 @ 16:21

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

Other Versions

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

16.9.0,
16.8.6, 16.8.5, 16.8.4, 16.8.3, 16.8.2, 16.8.1, 16.8.0,
16.7.0,
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
4724 bytes -1 byte zopfli --i100000 --mls8192 --bsr23 --lazy --ohh August 7, 2019 @ 18:33
4725 bytes zopfli --i100 --mls8192 --bsr23 --lazy --ohh August 7, 2019 @ 16:35

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

Most recent activity on August 8, 2019 @ 16:51.

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
4730 4730 4730 4729 4730 4730 4729 4728 4728 4728 4728 4726 4726 4726 4726
4730 4730 4730 4730 4728 4728 4729 4729 4728 4728 4728 4725 4725 4725 4725
4732 4732 4729 4729 4729 4728 4730 4729 4728 4728 4728 4725 4728 4730 4730
4729 4729 4731 4730 4727 4728 4730 4729 4728 4728 4728 4725 4725 4730 4730
4729 4729 4729 4729 4729 4729 4729 4728 4728 4728 4728 4726 4726 4726 4726
4729 4729 4729 4729 4731 4729 4729 4728 4728 4728 4728 4725 4726 4725 4725
4729 4729 4729 4729 4729 4729 4729 4729 4728 4728 4728 4726 4728 4728 4728
4728 4728 4729 4729 4728 4728 4728 4729 4728 4728 4728 4725 4725 4725 4725
4729 4729 4729 4729 4729 4728 4729 4729 4728 4728 4728 4727 4725 4726 4726
4730 4730 4729 4729 4726 4730 4728 4729 4728 4728 4728 4728 4726 4725 4725
4729 4729 4729 4729 4728 4731 4729 4728 4728 4728 4728 4726 4728 4727 4727
4729 4729 4729 4729 4729 4730 4729 4728 4728 4728 4728 4725 4725 4725 4725
4730 4730 4729 4730 4731 4730 4728 4729 4728 4728 4728 4725 4725 4725 4725
4729 4729 4729 4729 4729 4729 4728 4729 4728 4728 4728 4725 4726 4726 4726
4729 4729 4729 4729 4730 4730 4729 4728 4728 4728 4728 4726 4725 4725 4725
4730 4730 4729 4729 4729 4730 4729 4729 4728 4728 4728 4726 4728 4725 4725
4729 4729 4729 4729 4729 4729 4729 4729 4728 4728 4728 4725 4725 4725 4725
4728 4728 4729 4726 4730 4729 4729 4729 4728 4728 4728 4725 4725 4726 4726
4729 4729 4729 4729 4729 4729 4729 4729 4728 4728 4728 4725 4725 4725 4725
4729 4729 4729 4726 4729 4729 4729 4729 4728 4728 4728 4725 4724 4725 4725
4730 4730 4729 4729 4731 4730 4729 4728 4728 4728 4728 4726 4726 4726 4726
4728 4728 4729 4730 4729 4729 4729 4728 4728 4728 4728 4726 4726 4725 4725
4729 4729 4729 4730 4730 4729 4729 4728 4728 4728 4728 4726 4726 4725 4725

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 4725 bytes 100%
1,000 4725 bytes 100%
10,000 4725 bytes 100%
100,000 4724 bytes -1 byte 14.20%
1,000,000 4724 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
4729 bytes +5 bytes (+0.11%) +1 byte
4728 bytes +4 bytes (+0.08%)
4743 bytes +19 bytes (+0.40%) +15 bytes
4771 bytes +47 bytes (+0.99%) +43 bytes
4793 bytes +69 bytes (+1.46%) +65 bytes
4828 bytes +104 bytes (+2.20%) +100 bytes
4857 bytes +133 bytes (+2.82%) +129 bytes
4887 bytes +163 bytes (+3.45%) +159 bytes
4925 bytes +201 bytes (+4.25%) +197 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 4238 bytes -486 bytes (-10.29%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4336 bytes -388 bytes (-8.21%)
Zstandard (Wikipedia) zstd zstd -19 4709 bytes -15 bytes (-0.32%)
LZMA2 (Wikipedia) xz xz -9 4760 bytes +36 bytes (+0.76%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4868 bytes +144 bytes (+3.05%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4876 bytes +152 bytes (+3.22%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5108 bytes +384 bytes (+8.13%)

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 2019.
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