Choose a version:
12% The original file has 97676 bytes (95.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 11771 bytes (11.5k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4703 bytes (4.6k)
local copy
gzip -9
  4698 bytes (4.6k)
local copy
Boot
  4691 bytes (4.6k)
CDN
cdnjs
  4691 bytes (4.6k)
CDN
jsdelivr
  4683 bytes (4.6k)
CDN
7zip -mx=9 -tgzip
  4611 bytes (4.5k)
local copy
libdeflate -12
  4610 bytes (4.5k)
local copy
kzip -s0 -rn -b0
  4608 bytes (4.5k)
local copy
pigz -11 -n
  4606 bytes (4.5k)
local copy
Zopfli
  4605 bytes (4.5k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.6.1.min.js (or via HTTPS)

You will automatically get the smallest React 16.6.1 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 78 bytes by using my React 16.6.1 Zopfli version instead of the best available CDN (1.69% smaller than jsdelivr, 4605 vs. 4683 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 --mls16 --bsr13 --lazy --ohh

(found November 8, 2018)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 16  --mls16
block splitting recursion 13  --bsr13
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-16.6.1.min.js --location | md5sum
54d4015c4107861cbdc9734d393b8772  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.6.1.min.zopfli.js.gz | md5sum
54d4015c4107861cbdc9734d393b8772  -

SHA1:
curl --silent --compressed https://fb.me/react-16.6.1.min.js --location | sha1sum
52aa4316fb722ae38cef66a5e00fd943dd892c0d  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.6.1.min.zopfli.js.gz | sha1sum
52aa4316fb722ae38cef66a5e00fd943dd892c0d  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 4691 bytes 54d4015c4107861cbdc9734d393b8772 November 7, 2018 @ 04:00
cdnjs 4691 bytes 54d4015c4107861cbdc9734d393b8772 November 7, 2018 @ 04:00
jsdelivr 4683 bytes 54d4015c4107861cbdc9734d393b8772 November 8, 2018 @ 14:27

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

Other Versions

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

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
4605 bytes -1 byte zopfli --i100000 --mls16 --bsr13 --lazy --ohh November 8, 2018 @ 15:47
4606 bytes zopfli --i100 --mls1024 --bsr23 --lazy --ohh November 8, 2018 @ 14:28

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

Most recent activity on November 8, 2018 @ 17:12.

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
4613 4613 4615 4606 4606 4615 4616 4606 4606 4606 4606 4606 4609 4609 4609
4606 4606 4606 4606 4606 4611 4606 4611 4606 4606 4606 4606 4608 4608 4608
4606 4606 4606 4606 4606 4606 4611 4615 4606 4606 4606 4606 4608 4608 4608
4606 4606 4611 4614 4614 4606 4606 4614 4606 4606 4606 4606 4612 4608 4608
4606 4606 4615 4614 4606 4615 4611 4614 4606 4606 4606 4606 4609 4608 4608
4614 4614 4613 4612 4614 4606 4606 4606 4606 4606 4606 4606 4613 4613 4613
4606 4606 4613 4613 4606 4614 4615 4613 4606 4606 4606 4606 4614 4613 4613
4606 4606 4613 4606 4606 4606 4606 4614 4606 4606 4606 4606 4607 4611 4611
4606 4606 4610 4614 4606 4614 4615 4614 4606 4606 4606 4606 4608 4609 4609
4606 4606 4606 4605 4606 4606 4606 4613 4606 4606 4606 4606 4613 4613 4613
4613 4613 4613 4613 4614 4614 4606 4614 4606 4606 4606 4606 4608 4612 4612
4611 4611 4610 4613 4614 4611 4612 4614 4606 4606 4606 4606 4612 4608 4608
4612 4612 4613 4613 4614 4615 4611 4612 4606 4606 4606 4606 4608 4608 4608
4606 4606 4606 4614 4614 4615 4611 4614 4606 4606 4606 4606 4614 4612 4612
4606 4606 4606 4613 4614 4607 4613 4613 4606 4606 4606 4606 4607 4608 4608
4613 4613 4613 4613 4614 4614 4613 4613 4606 4606 4606 4606 4614 4608 4608
4611 4611 4611 4614 4614 4614 4611 4611 4606 4606 4606 4606 4608 4608 4608
4606 4606 4610 4614 4614 4614 4611 4611 4606 4606 4606 4606 4608 4608 4608
4611 4611 4610 4614 4614 4613 4613 4611 4606 4606 4606 4606 4607 4607 4607
4606 4606 4606 4614 4606 4614 4613 4614 4606 4606 4606 4606 4614 4608 4608
4606 4606 4613 4613 4606 4607 4613 4612 4606 4606 4606 4606 4608 4608 4608
4611 4611 4611 4613 4614 4611 4613 4613 4606 4606 4606 4606 4608 4608 4608
4611 4611 4612 4613 4615 4612 4614 4613 4606 4606 4606 4606 4608 4608 4608

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 4606 bytes 100%
1,000 4606 bytes 100%
10,000 4606 bytes 100%
100,000 4605 bytes -1 byte 44.06%
1,000,000 4605 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
4608 bytes +3 bytes (+0.07%)
4608 bytes +3 bytes (+0.07%)
4623 bytes +18 bytes (+0.39%) +15 bytes
4653 bytes +48 bytes (+1.04%) +45 bytes
4669 bytes +64 bytes (+1.39%) +61 bytes
4708 bytes +103 bytes (+2.24%) +100 bytes
4742 bytes +137 bytes (+2.98%) +134 bytes
4772 bytes +167 bytes (+3.63%) +164 bytes
4803 bytes +198 bytes (+4.30%) +195 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 4129 bytes -476 bytes (-10.34%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4227 bytes -378 bytes (-8.21%)
Zstandard (Wikipedia) zstd zstd -19 4614 bytes +9 bytes (+0.20%)
LZMA2 (Wikipedia) xz xz -9 4648 bytes +43 bytes (+0.93%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4764 bytes +159 bytes (+3.45%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4780 bytes +175 bytes (+3.80%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5020 bytes +415 bytes (+9.01%)

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