Choose a version:
11% The original file has 120044 bytes (117.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 13317 bytes (13.0k, 11%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  5199 bytes (5.1k)
local copy
gzip -9
  5197 bytes (5.1k)
local copy
Boot
  5186 bytes (5.1k)
CDN
cdnjs
  5186 bytes (5.1k)
CDN
jsdelivr
  5179 bytes (5.1k)
CDN
libdeflate -12
  5098 bytes (5.0k)
local copy
pigz -11 -n
  5097 bytes (5.0k)
local copy
7zip -mx=9 -tgzip
  5093 bytes (5.0k)
local copy
kzip -s0 -rn -b0
  5093 bytes (5.0k)
local copy
Zopfli
  5086 bytes (5.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.9.0.min.js (or via HTTPS)

You will automatically get the smallest React 16.9.0 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 93 bytes by using my React 16.9.0 Zopfli version instead of the best available CDN (1.83% smaller than jsdelivr, 5086 vs. 5179 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 9, 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-16.9.0.min.js --location | md5sum
f80458708d0a9701b76d741d35b6722f  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.9.0.min.zopfli.js.gz | md5sum
f80458708d0a9701b76d741d35b6722f  -

SHA1:
curl --silent --compressed https://fb.me/react-16.9.0.min.js --location | sha1sum
7df21035302d6fe31fb09ae7a35432db12a6b352  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.9.0.min.zopfli.js.gz | sha1sum
7df21035302d6fe31fb09ae7a35432db12a6b352  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 5186 bytes f80458708d0a9701b76d741d35b6722f August 8, 2019 @ 23:45
cdnjs 5186 bytes f80458708d0a9701b76d741d35b6722f August 8, 2019 @ 23:46
jsdelivr 5179 bytes f80458708d0a9701b76d741d35b6722f August 9, 2019 @ 11:59

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
5086 bytes -1 byte zopfli --i100000 --mls8192 --bsr23 --lazy --ohh August 9, 2019 @ 13:09
5087 bytes -1 byte zopfli --i1000 --mls4096 --bsr10 --lazy --ohh August 9, 2019 @ 12:33
5088 bytes -1 byte zopfli --i1000 --mls256 --bsr30 --lazy --ohh August 9, 2019 @ 12:33
5089 bytes zopfli --i100 --mls256 --bsr15 --lazy --ohh August 9, 2019 @ 12:01

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

Most recent activity on August 9, 2019 @ 14:18.

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
5091 5091 5091 5091 5089 5089 5091 5092 5092 5092 5091 5091 5089 5089 5089
5094 5094 5095 5094 5089 5093 5088 5088 5092 5092 5091 5089 5096 5091 5091
5089 5089 5092 5088 5089 5089 5088 5095 5092 5090 5091 5090 5090 5091 5091
5098 5098 5089 5088 5090 5089 5089 5088 5092 5091 5090 5091 5086 5090 5090
5090 5090 5091 5092 5089 5089 5092 5088 5092 5092 5091 5089 5087 5089 5089
5089 5089 5091 5091 5089 5089 5091 5088 5092 5092 5091 5089 5090 5090 5090
5089 5089 5092 5088 5088 5088 5088 5088 5092 5089 5090 5087 5091 5090 5090
5091 5091 5092 5088 5089 5091 5088 5088 5092 5092 5091 5089 5091 5089 5089
5089 5089 5088 5090 5089 5089 5088 5088 5092 5090 5089 5090 5086 5091 5091
5089 5089 5092 5089 5088 5089 5088 5088 5092 5091 5089 5091 5088 5089 5089
5088 5088 5092 5093 5093 5088 5094 5092 5092 5090 5089 5091 5088 5089 5089
5088 5088 5089 5089 5090 5089 5089 5086 5092 5091 5091 5090 5089 5090 5090
5088 5088 5089 5088 5090 5089 5088 5088 5092 5091 5091 5093 5088 5089 5089
5088 5088 5097 5089 5090 5089 5092 5092 5092 5092 5091 5091 5089 5089 5089
5093 5093 5092 5092 5088 5088 5088 5088 5092 5092 5091 5089 5088 5089 5089
5090 5090 5090 5089 5088 5094 5091 5091 5092 5090 5091 5090 5089 5089 5089
5088 5088 5089 5089 5089 5089 5091 5095 5092 5089 5091 5090 5091 5091 5091
5098 5098 5092 5093 5089 5094 5089 5088 5092 5090 5091 5089 5095 5087 5087
5089 5089 5088 5089 5089 5089 5088 5088 5092 5089 5091 5090 5088 5091 5091
5089 5089 5091 5088 5089 5089 5088 5092 5092 5089 5091 5089 5086 5091 5091
5089 5089 5089 5089 5089 5089 5088 5089 5092 5090 5091 5090 5088 5091 5091
5097 5097 5092 5092 5089 5089 5094 5088 5092 5090 5091 5089 5089 5091 5091
5098 5098 5089 5089 5088 5089 5088 5088 5092 5090 5091 5088 5091 5091 5091

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 5089 bytes 100%
1,000 5087 bytes -2 bytes 100%
10,000 5087 bytes 100%
100,000 5086 bytes -1 byte 2.32%
1,000,000 5086 bytes 1.16%
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
5093 bytes +7 bytes (+0.14%)
5095 bytes +9 bytes (+0.18%) +2 bytes
5111 bytes +25 bytes (+0.49%) +18 bytes
5140 bytes +54 bytes (+1.06%) +47 bytes
5172 bytes +86 bytes (+1.69%) +79 bytes
5197 bytes +111 bytes (+2.18%) +104 bytes
5209 bytes +123 bytes (+2.42%) +116 bytes
5240 bytes +154 bytes (+3.03%) +147 bytes
5274 bytes +188 bytes (+3.70%) +181 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 4547 bytes -539 bytes (-10.60%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4651 bytes -435 bytes (-8.55%)
Zstandard (Wikipedia) zstd zstd -19 5071 bytes -15 bytes (-0.29%)
LZMA2 (Wikipedia) xz xz -9 5088 bytes +2 bytes (+0.04%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 5209 bytes +123 bytes (+2.42%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 5211 bytes +125 bytes (+2.46%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5382 bytes +296 bytes (+5.82%)

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