Choose a version:
11% The original file has 115653 bytes (112.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12588 bytes (12.3k, 11%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  4959 bytes (4.8k)
local copy
gzip -9
  4957 bytes (4.8k)
local copy
Boot
  4940 bytes (4.8k)
CDN
cdnjs
  4940 bytes (4.8k)
CDN
jsdelivr
  4938 bytes (4.8k)
CDN
kzip -s0 -rn -b1
  4857 bytes (4.7k)
local copy
libdeflate -12
  4857 bytes (4.7k)
local copy
7zip -mx=9 -tgzip
  4854 bytes (4.7k)
local copy
pigz -11 -n
  4854 bytes (4.7k)
local copy
Zopfli
  4848 bytes (4.7k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/react/react-16.12.0.min.js (or via HTTPS)

You will automatically get the smallest React 16.12.0 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 90 bytes by using my React 16.12.0 Zopfli version instead of the best available CDN (1.86% smaller than jsdelivr, 4848 vs. 4938 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 --mls32768 --bsr18 --lazy --ohh

(found November 18, 2019)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 32768  --mls32768
block splitting recursion 18  --bsr18
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-16.12.0.min.js --location | md5sum
0647cbbcb7475b4ec406caac8c5e6258  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.12.0.min.zopfli.js.gz | md5sum
0647cbbcb7475b4ec406caac8c5e6258  -

SHA1:
curl --silent --compressed https://fb.me/react-16.12.0.min.js --location | sha1sum
e9a31ed770ed6c07bf265b68dcb3f7673aa5ec7d  -
curl --silent --compressed https://minime.stephan-brumme.com/files/react/react-16.12.0.min.zopfli.js.gz | sha1sum
e9a31ed770ed6c07bf265b68dcb3f7673aa5ec7d  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 4940 bytes 0647cbbcb7475b4ec406caac8c5e6258 December 4, 2019 @ 13:46
cdnjs 4940 bytes 0647cbbcb7475b4ec406caac8c5e6258 December 4, 2019 @ 13:46
jsdelivr 4938 bytes 0647cbbcb7475b4ec406caac8c5e6258 November 18, 2019 @ 10:01

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

Other Versions

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

16.12.0,
16.11.0,
16.10.2, 16.10.1, 16.10.0,
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
4848 bytes -1 byte zopfli --i100000 --mls32768 --bsr18 --lazy --ohh November 18, 2019 @ 11:33
4849 bytes zopfli --i100 --mls512 --bsr15 --lazy --ohh November 18, 2019 @ 10:05

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

Most recent activity on December 4, 2019 @ 13:46.

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
4855 4855 4854 4854 4855 4855 4854 4854 4853 4853 4853 4853 4853 4853 4853
4850 4850 4850 4850 4850 4850 4854 4852 4853 4853 4853 4853 4854 4855 4855
4855 4855 4852 4853 4852 4852 4852 4850 4851 4853 4853 4853 4850 4854 4854
4852 4852 4854 4854 4852 4852 4850 4850 4848 4853 4853 4853 4854 4851 4851
4852 4852 4854 4854 4855 4855 4850 4853 4849 4853 4853 4853 4853 4851 4851
4851 4851 4852 4853 4852 4850 4849 4850 4850 4853 4853 4853 4854 4855 4855
4855 4855 4854 4853 4852 4852 4849 4850 4851 4853 4853 4853 4855 4855 4855
4854 4854 4854 4853 4852 4852 4849 4850 4849 4853 4853 4853 4852 4855 4855
4854 4854 4854 4853 4852 4852 4850 4849 4853 4853 4853 4853 4851 4853 4853
4855 4855 4855 4853 4851 4852 4850 4849 4849 4853 4853 4853 4855 4852 4852
4855 4855 4852 4853 4852 4850 4850 4850 4853 4853 4853 4853 4852 4851 4851
4852 4852 4852 4853 4852 4851 4849 4850 4848 4853 4853 4853 4854 4855 4855
4852 4852 4852 4854 4852 4851 4850 4850 4849 4853 4853 4853 4854 4848 4848
4854 4854 4852 4853 4852 4852 4849 4850 4848 4853 4853 4853 4855 4854 4854
4854 4854 4852 4852 4852 4852 4850 4850 4849 4853 4853 4853 4850 4848 4848
4854 4854 4854 4852 4852 4852 4850 4850 4850 4853 4853 4853 4855 4852 4852
4854 4854 4852 4852 4852 4854 4850 4850 4850 4853 4853 4853 4855 4854 4854
4854 4854 4852 4853 4852 4852 4850 4851 4848 4853 4853 4853 4853 4850 4850
4851 4851 4852 4852 4852 4852 4850 4850 4850 4853 4853 4853 4852 4852 4852
4854 4854 4854 4853 4852 4852 4850 4850 4852 4853 4853 4853 4852 4854 4854
4852 4852 4852 4852 4853 4851 4850 4850 4850 4853 4853 4853 4851 4855 4855
4854 4854 4855 4852 4852 4852 4850 4850 4849 4853 4853 4853 4855 4852 4852
4852 4852 4852 4853 4851 4850 4849 4850 4849 4853 4853 4853 4854 4852 4852

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 4849 bytes 100%
1,000 4849 bytes 100%
10,000 4849 bytes 100%
100,000 4848 bytes -1 byte 6.67%
1,000,000 4848 bytes 2.32%
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
4857 bytes +9 bytes (+0.19%)
4857 bytes +9 bytes (+0.19%)
4872 bytes +24 bytes (+0.50%) +15 bytes
4891 bytes +43 bytes (+0.89%) +34 bytes
4929 bytes +81 bytes (+1.67%) +72 bytes
4943 bytes +95 bytes (+1.96%) +86 bytes
4974 bytes +126 bytes (+2.60%) +117 bytes
5006 bytes +158 bytes (+3.26%) +149 bytes
5047 bytes +199 bytes (+4.10%) +190 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 4367 bytes -481 bytes (-9.92%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 4454 bytes -394 bytes (-8.13%)
Zstandard (Wikipedia) zstd zstd -19 4850 bytes +2 bytes (+0.04%)
LZMA2 (Wikipedia) xz xz -9 4888 bytes +40 bytes (+0.83%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 4962 bytes +114 bytes (+2.35%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 4981 bytes +133 bytes (+2.74%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5219 bytes +371 bytes (+7.65%)

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

All trademarks are property of their respective owners. You know, the boring legal stuff.