Choose a version:
44% The original file has 135079 bytes (131.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 60010 bytes (58.6k, 44%).

After GZIP compression these minified files vary in size:
unpkg
  19745 bytes (19.3k)
CDN
cdnjs
  16116 bytes (15.7k)
CDN
gzip -6 (default)
  15941 bytes (15.6k)
local copy
MaxCDN
  15918 bytes (15.5k)
CDN
jsdelivr
  15918 bytes (15.5k)
CDN
gzip -9
  15875 bytes (15.5k)
local copy
7zip -mx=9 -tgzip
  15370 bytes (15.0k)
local copy
libdeflate -12
  15369 bytes (15.0k)
local copy
kzip -s0 -rn -b2
  15341 bytes (15.0k)
local copy
zultra
  15332 bytes (15.0k)
local copy
pigz -11 -n
  15316 bytes (15.0k)
local copy
Zopfli
  15306 bytes (14.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-4.4.0.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 4.4.0 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 612 bytes by using my Bootstrap 4.4.0 Zopfli version instead of the best available CDN (4.00% smaller than jsdelivr, 15306 vs. 15918 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 --i1000000 --mb8 --mls8 --bsr10 --lazy --ohh

(found November 27, 2019)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 8  --mls8
block splitting recursion 10  --bsr10
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://raw.githubusercontent.com/twbs/bootstrap/v4.4.0/dist/js/bootstrap.min.js --location | md5sum
bee4d04313ec19beb661e72d744b2349  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-4.4.0.min.zopfli.js.gz | md5sum
bee4d04313ec19beb661e72d744b2349  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v4.4.0/dist/js/bootstrap.min.js --location | sha1sum
acb9808a2dee2fd74636525c4c069e2cb80c5927  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-4.4.0.min.zopfli.js.gz | sha1sum
acb9808a2dee2fd74636525c4c069e2cb80c5927  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 19745 bytes bee4d04313ec19beb661e72d744b2349 (invalid)
cdnjs 16116 bytes bee4d04313ec19beb661e72d744b2349 March 27, 2020 @ 17:16
MaxCDN 15918 bytes bee4d04313ec19beb661e72d744b2349 (invalid)
jsdelivr 15918 bytes bee4d04313ec19beb661e72d744b2349 December 1, 2019 @ 05:24

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

Other Versions

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

4.5.0,
4.4.1, 4.4.0,
4.3.1, 4.3.0,
4.2.1, 4.2.0,
4.1.3, 4.1.2, 4.1.1, 4.1.0,
4.0.0,
3.4.1, 3.4.0,
3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.2, 3.3.1, 3.3.0,
3.2.0,
3.1.1, 3.1.0,
3.0.3, 3.0.2, 3.0.1, 3.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
15306 bytes -1 byte zopfli --i1000000 --mls8 --bsr10 --lazy --ohh November 27, 2019 @ 15:33
15307 bytes -1 byte zopfli --i100000 --mls8 --bsr10 --lazy --ohh November 27, 2019 @ 12:34
15308 bytes -1 byte zopfli --i10000 --mls16384 --bsr21 --lazy --ohh November 27, 2019 @ 08:09
15309 bytes -1 byte zopfli --i10000 --mls32 --bsr13 --lazy --ohh November 27, 2019 @ 08:06
15310 bytes -1 byte zopfli --i1000 --mls16384 --bsr21 --lazy --ohh November 27, 2019 @ 07:47
15311 bytes zopfli --i100 --mls2048 --bsr23 --lazy --ohh November 27, 2019 @ 07:37

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

Most recent activity on July 20, 2020 @ 12:54.

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
15314 15314 15321 15315 15323 15314 15315 15317 15315 15317 15309 15319 15323 15311 15323
15310 15308 15311 15309 15308 15310 15310 15312 15311 15309 15310 15319 15323 15309 15319
15308 15309 15308 15309 15309 15309 15309 15310 15309 15309 15309 15323 15322 15310 15320
15310 15310 15309 15309 15309 15309 15309 15311 15310 15309 15309 15311 15324 15311 15326
15310 15310 15309 15312 15309 15309 15310 15312 15309 15309 15309 15310 15323 15309 15327
15308 15308 15310 15311 15309 15312 15310 15312 15309 15309 15310 15324 15322 15310 15310
15309 15308 15306 15310 15309 15309 15310 15312 15309 15309 15308 15314 15322 15309 15326
15309 15309 15309 15312 15309 15309 15309 15310 15309 15309 15310 15309 15323 15308 15327
15309 15310 15308 15312 15309 15309 15310 15312 15311 15309 15309 15310 15321 15309 15320
15309 15309 15308 15309 15309 15309 15310 15312 15309 15309 15309 15324 15322 15317 15327
15308 15310 15310 15312 15309 15309 15310 15311 15308 15309 15310 15314 15321 15311 15327
15310 15310 15309 15309 15309 15309 15310 15312 15309 15309 15309 15311 15323 15311 15321
15308 15309 15309 15309 15309 15310 15310 15312 15308 15309 15310 15325 15321 15310 15322
15309 15309 15309 15309 15309 15309 15308 15312 15311 15308 15309 15323 15321 15323 15320
15308 15308 15309 15309 15310 15309 15310 15312 15309 15310 15311 15312 15322 15312 15322
15308 15308 15308 15312 15309 15309 15310 15311 15308 15325 15309 15311 15322 15308 15320
15309 15309 15306 15311 15310 15309 15309 15311 15309 15310 15309 15314 15324 15310 15320
15309 15309 15309 15312 15309 15309 15309 15310 15309 15309 15309 15325 15321 15308 15321
15308 15308 15308 15309 15309 15310 15308 15311 15309 15310 15309 15324 15321 15310 15327
15309 15309 15308 15311 15309 15309 15310 15311 15310 15309 15309 15324 15322 15310 15327
15308 15309 15309 15312 15309 15309 15308 15312 15309 15309 15309 15324 15322 15310 15320
15309 15309 15308 15309 15309 15309 15308 15310 15309 15309 15310 15314 15321 15310 15322
15309 15309 15308 15311 15309 15309 15309 15312 15308 15310 15308 15323 15322 15323 15323

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 15311 bytes 100%
1,000 15310 bytes -1 byte 100%
10,000 15308 bytes -2 bytes 100%
100,000 15307 bytes -1 byte 11.30%
1,000,000 15306 bytes -1 byte 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
15380 bytes +74 bytes (+0.48%) +39 bytes
15380 bytes +74 bytes (+0.48%) +39 bytes
15341 bytes +35 bytes (+0.23%)
15344 bytes +38 bytes (+0.25%) +3 bytes
15353 bytes +47 bytes (+0.31%) +12 bytes
15382 bytes +76 bytes (+0.50%) +41 bytes
15413 bytes +107 bytes (+0.70%) +72 bytes
15444 bytes +138 bytes (+0.90%) +103 bytes
15479 bytes +173 bytes (+1.13%) +138 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 - for example, your browser actually supports it !
Algorithm Program Parameters Size Compared To Best Zopfli
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 12748 bytes -2558 bytes (-16.71%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 13034 bytes -2272 bytes (-14.84%)
Brotli (Wikipedia) brotli brotli -q 11 13944 bytes -1362 bytes (-8.90%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 14711 bytes -595 bytes (-3.89%)
LZMA2 (Wikipedia) xz xz -9 14764 bytes -542 bytes (-3.54%)
Zstandard (Wikipedia) zstd zstd -19 14972 bytes -334 bytes (-2.18%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 15274 bytes -32 bytes (-0.21%)

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 2020.
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.