Choose a version:
12% The original file has 102553 bytes (100.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12682 bytes (12.4k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4908 bytes (4.8k)
local copy
gzip -9
  4903 bytes (4.8k)
local copy
cdnjs
  4896 bytes (4.8k)
CDN
Boot
  4888 bytes (4.8k)
CDN
jsdelivr
  4888 bytes (4.8k)
CDN
7zip -mx=9 -tgzip
  4808 bytes (4.7k)
local copy
libdeflate -12
  4808 bytes (4.7k)
local copy
pigz -11 -n
  4808 bytes (4.7k)
local copy
kzip -s0 -rn -b1
  4805 bytes (4.7k)
local copy
Zopfli
  4800 bytes (4.7k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.8.6.min.js (or via HTTPS)

You will automatically get the smallest React 16.8.6 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 88 bytes by using my React 16.8.6 Zopfli version instead of the best available CDN (1.83% smaller than jsdelivr, 4800 vs. 4888 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 --i10000 --mb8 --mls32 --bsr30 --lazy --ohh

(found August 7, 2019)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 32  --mls32
block splitting recursion 30  --bsr30
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-16.8.6.min.js --location | md5sum
f808b8e8ab51b0d9525795db3768cd86  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.8.6.min.zopfli.js.gz | md5sum
f808b8e8ab51b0d9525795db3768cd86  -

SHA1:
curl --silent --compressed https://fb.me/react-16.8.6.min.js --location | sha1sum
da282c1a379fe3b12bc064159bdf5cb3c7b70d13  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.8.6.min.zopfli.js.gz | sha1sum
da282c1a379fe3b12bc064159bdf5cb3c7b70d13  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
cdnjs 4896 bytes f808b8e8ab51b0d9525795db3768cd86 March 28, 2019 @ 08:00
Boot 4888 bytes f808b8e8ab51b0d9525795db3768cd86 March 28, 2019 @ 08:00
jsdelivr 4888 bytes f808b8e8ab51b0d9525795db3768cd86 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
4800 bytes -1 byte zopfli --i10000 --mls32 --bsr30 --lazy --ohh August 7, 2019 @ 17:16
4801 bytes -1 byte zopfli --i1000 --mls32 --bsr30 --lazy --ohh August 7, 2019 @ 17:09
4802 bytes zopfli --i100 --mls32 --bsr30 --lazy --ohh August 7, 2019 @ 16:29

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

Most recent activity on August 7, 2019 @ 22:17.

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
4805 4805 4805 4812 4808 4805 4809 4808 4805 4805 4805 4804 4804 4804 4804
4805 4805 4805 4805 4805 4805 4805 4809 4805 4805 4805 4805 4810 4807 4807
4805 4805 4805 4805 4807 4805 4807 4810 4805 4805 4805 4805 4810 4803 4803
4805 4805 4805 4805 4802 4805 4806 4808 4805 4805 4805 4803 4803 4803 4803
4808 4808 4805 4808 4807 4808 4808 4807 4805 4805 4805 4804 4804 4804 4804
4805 4805 4805 4806 4806 4805 4808 4806 4805 4805 4805 4803 4809 4812 4812
4809 4809 4808 4807 4807 4808 4808 4808 4805 4805 4805 4804 4808 4808 4808
4805 4805 4805 4805 4807 4805 4807 4808 4805 4805 4805 4803 4803 4803 4803
4807 4807 4808 4807 4806 4805 4808 4810 4805 4805 4804 4806 4810 4810 4810
4805 4805 4808 4807 4807 4808 4808 4806 4805 4805 4805 4804 4803 4804 4804
4807 4807 4808 4806 4807 4808 4807 4808 4805 4805 4804 4803 4808 4809 4809
4808 4808 4808 4807 4807 4808 4808 4807 4805 4805 4805 4804 4803 4803 4803
4808 4808 4808 4807 4806 4808 4808 4807 4805 4805 4805 4803 4803 4810 4810
4805 4805 4805 4808 4807 4808 4808 4808 4805 4805 4805 4803 4803 4804 4804
4807 4807 4807 4808 4807 4808 4808 4808 4805 4805 4805 4804 4804 4804 4804
4805 4805 4807 4808 4807 4808 4808 4808 4805 4805 4805 4803 4810 4811 4811
4807 4807 4808 4809 4807 4809 4808 4808 4805 4805 4805 4803 4803 4803 4803
4805 4805 4808 4807 4807 4808 4807 4808 4805 4805 4805 4803 4803 4803 4803
4808 4808 4808 4808 4806 4808 4808 4806 4805 4805 4805 4803 4803 4803 4803
4807 4807 4808 4807 4807 4805 4807 4808 4805 4805 4804 4804 4810 4803 4803
4809 4809 4807 4807 4808 4809 4809 4807 4805 4805 4805 4804 4810 4810 4810
4805 4805 4809 4807 4800 4800 4808 4808 4805 4805 4805 4804 4803 4803 4803
4807 4807 4807 4807 4807 4809 4807 4807 4805 4805 4805 4803 4803 4803 4803

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 4802 bytes 100%
1,000 4801 bytes -1 byte 100%
10,000 4800 bytes -1 byte 100%
100,000 4800 bytes 1.74%
1,000,000 4800 bytes 0.58%
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
4807 bytes +7 bytes (+0.15%) +2 bytes
4805 bytes +5 bytes (+0.10%)
4818 bytes +18 bytes (+0.38%) +13 bytes
4846 bytes +46 bytes (+0.96%) +41 bytes
4870 bytes +70 bytes (+1.46%) +65 bytes
4905 bytes +105 bytes (+2.19%) +100 bytes
4934 bytes +134 bytes (+2.79%) +129 bytes
4965 bytes +165 bytes (+3.44%) +160 bytes
4987 bytes +187 bytes (+3.90%) +182 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 4318 bytes -482 bytes (-10.04%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4401 bytes -399 bytes (-8.31%)
Zstandard (Wikipedia) zstd zstd -19 4789 bytes -11 bytes (-0.23%)
LZMA2 (Wikipedia) xz xz -9 4836 bytes +36 bytes (+0.75%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4934 bytes +134 bytes (+2.79%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4955 bytes +155 bytes (+3.23%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5166 bytes +366 bytes (+7.63%)

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