Choose a version:
12% The original file has 95936 bytes (93.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 11933 bytes (11.7k, 12%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4740 bytes (4.6k)
local copy
gzip -9
  4736 bytes (4.6k)
local copy
Boot
  4727 bytes (4.6k)
CDN
cdnjs
  4727 bytes (4.6k)
CDN
jsdelivr
  4720 bytes (4.6k)
CDN
7zip -mx=9 -tgzip
  4652 bytes (4.5k)
local copy
libdeflate -12
  4651 bytes (4.5k)
local copy
kzip -s0 -rn -b0
  4649 bytes (4.5k)
local copy
pigz -11 -n
  4648 bytes (4.5k)
local copy
Zopfli
  4643 bytes (4.5k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.6.0.min.js (or via HTTPS)

You will automatically get the smallest React 16.6.0 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 77 bytes by using my React 16.6.0 Zopfli version instead of the best available CDN (1.66% smaller than jsdelivr, 4643 vs. 4720 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 --mls32768 --bsr20 --lazy --ohh

(found October 25, 2018)
Description Value Parameter
iterations 1000  --i1000
maximum blocks 8  --mb8
maximum length score 32768  --mls32768
block splitting recursion 20  --bsr20
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-16.6.0.min.js --location | md5sum
dd01c48151e8cc10ee1543922ab744db  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.6.0.min.zopfli.js.gz | md5sum
dd01c48151e8cc10ee1543922ab744db  -

SHA1:
curl --silent --compressed https://fb.me/react-16.6.0.min.js --location | sha1sum
fff417ea70ff9f65c8a5f68b239065d9f29337ed  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.6.0.min.zopfli.js.gz | sha1sum
fff417ea70ff9f65c8a5f68b239065d9f29337ed  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 4727 bytes dd01c48151e8cc10ee1543922ab744db October 24, 2018 @ 19:00
cdnjs 4727 bytes dd01c48151e8cc10ee1543922ab744db October 24, 2018 @ 19:00
jsdelivr 4720 bytes dd01c48151e8cc10ee1543922ab744db October 25, 2018 @ 12:12

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

Other Versions

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

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
4643 bytes -2 bytes zopfli --i1000 --mls32768 --bsr20 --lazy --ohh October 25, 2018 @ 13:12
4645 bytes zopfli --i100 --mls4096 --bsr18 --lazy --ohh October 25, 2018 @ 12:20

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

Most recent activity on October 25, 2018 @ 14:39.

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
4651 4651 4651 4651 4648 4648 4648 4648 4648 4648 4648 4648 4650 4650 4650
4648 4648 4648 4647 4648 4648 4651 4648 4648 4648 4648 4643 4649 4646 4646
4648 4648 4648 4648 4648 4648 4648 4649 4648 4648 4648 4647 4649 4649 4649
4648 4648 4648 4648 4648 4648 4648 4648 4648 4643 4648 4646 4649 4649 4649
4647 4647 4647 4651 4650 4648 4651 4650 4648 4648 4648 4647 4649 4649 4649
4648 4648 4648 4646 4648 4648 4651 4649 4648 4643 4648 4648 4649 4649 4649
4648 4648 4647 4648 4648 4648 4647 4649 4648 4648 4648 4648 4649 4649 4649
4648 4648 4648 4648 4648 4648 4651 4648 4648 4643 4648 4647 4649 4649 4649
4647 4647 4651 4651 4647 4648 4647 4649 4648 4648 4648 4646 4650 4651 4651
4648 4648 4648 4648 4648 4648 4648 4649 4648 4648 4648 4646 4650 4649 4649
4650 4650 4652 4648 4648 4648 4650 4649 4648 4648 4648 4648 4649 4649 4649
4648 4648 4650 4648 4650 4650 4647 4649 4648 4648 4648 4646 4649 4649 4649
4647 4647 4647 4647 4651 4648 4650 4649 4648 4648 4648 4648 4645 4649 4649
4647 4647 4652 4651 4650 4648 4647 4650 4648 4648 4648 4647 4649 4649 4649
4648 4648 4647 4648 4651 4648 4648 4648 4648 4648 4648 4643 4649 4649 4649
4650 4650 4651 4647 4651 4650 4650 4650 4648 4648 4648 4648 4649 4649 4649
4647 4647 4650 4649 4647 4648 4648 4650 4648 4648 4648 4648 4648 4643 4643
4647 4647 4647 4648 4650 4650 4647 4650 4648 4648 4648 4648 4649 4649 4649
4647 4647 4647 4648 4650 4650 4647 4648 4648 4648 4648 4643 4649 4647 4647
4647 4647 4647 4648 4647 4650 4647 4650 4648 4648 4648 4646 4649 4650 4650
4648 4648 4647 4647 4651 4648 4649 4648 4648 4648 4648 4648 4648 4648 4648
4648 4648 4647 4651 4651 4650 4648 4648 4648 4648 4648 4647 4649 4649 4649
4647 4647 4647 4651 4651 4650 4651 4648 4648 4643 4648 4647 4650 4643 4643

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 4645 bytes 100%
1,000 4643 bytes -2 bytes 100%
10,000 4643 bytes 100%
100,000 4643 bytes 3.19%
1,000,000 4643 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
4649 bytes +6 bytes (+0.13%)
4649 bytes +6 bytes (+0.13%)
4662 bytes +19 bytes (+0.41%) +13 bytes
4688 bytes +45 bytes (+0.97%) +39 bytes
4705 bytes +62 bytes (+1.34%) +56 bytes
4743 bytes +100 bytes (+2.15%) +94 bytes
4775 bytes +132 bytes (+2.84%) +126 bytes
4798 bytes +155 bytes (+3.34%) +149 bytes
4832 bytes +189 bytes (+4.07%) +183 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 4165 bytes -478 bytes (-10.30%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4269 bytes -374 bytes (-8.06%)
Zstandard (Wikipedia) zstd zstd -19 4656 bytes +13 bytes (+0.28%)
LZMA2 (Wikipedia) xz xz -9 4680 bytes +37 bytes (+0.80%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4812 bytes +169 bytes (+3.64%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4812 bytes +169 bytes (+3.64%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5057 bytes +414 bytes (+8.92%)

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