Choose a version:
44% The original file has 144033 bytes (140.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 63467 bytes (62.0k, 44%).

After GZIP compression these minified files vary in size:
unpkg
  19158 bytes (18.7k)
CDN
gzip -6 (default)
  14983 bytes (14.6k)
local copy
jsdelivr
  14954 bytes (14.6k)
CDN
gzip -9
  14913 bytes (14.6k)
local copy
cdnjs
  14899 bytes (14.5k)
CDN
7zip -mx=9 -tgzip
  14428 bytes (14.1k)
local copy
libdeflate -12
  14416 bytes (14.1k)
local copy
kzip -s0 -rn -b2
  14380 bytes (14.0k)
local copy
zultra
  14374 bytes (14.0k)
local copy
pigz -11 -n
  14352 bytes (14.0k)
local copy
Zopfli
  14344 bytes (14.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-4.6.0.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 4.6.0 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 555 bytes by using my Bootstrap 4.6.0 Zopfli version instead of the best available CDN (3.87% smaller than cdnjs, 14344 vs. 14899 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 --mls1024 --bsr12 --lazy --ohh

(found January 27, 2021)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 1024  --mls1024
block splitting recursion 12  --bsr12
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/v4.6.0/dist/js/bootstrap.min.js --location | md5sum
f0c2bcf5ef0c4476508d79ec9cdcce07  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-4.6.0.min.zopfli.js.gz | md5sum
f0c2bcf5ef0c4476508d79ec9cdcce07  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v4.6.0/dist/js/bootstrap.min.js --location | sha1sum
3beed68ed7d753c6bf4f61c26386ddd7929ba030  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-4.6.0.min.zopfli.js.gz | sha1sum
3beed68ed7d753c6bf4f61c26386ddd7929ba030  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 19158 bytes f0c2bcf5ef0c4476508d79ec9cdcce07 (invalid)
jsdelivr 14954 bytes f0c2bcf5ef0c4476508d79ec9cdcce07 January 25, 2021 @ 08:38
cdnjs 14899 bytes f0c2bcf5ef0c4476508d79ec9cdcce07 (invalid)

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

Other Versions

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

4.6.0,
4.5.3, 4.5.2, 4.5.1, 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
14344 bytes -1 byte zopfli --i1000000 --mls1024 --bsr12 --lazy --ohh January 27, 2021 @ 19:33
14345 bytes -1 byte zopfli --i10000 --mls4 --bsr9 --lazy --ohh January 25, 2021 @ 10:31
14346 bytes -1 byte zopfli --i1000 --mls1024 --bsr7 --lazy --ohh January 25, 2021 @ 09:17
14347 bytes -1 byte zopfli --i1000 --mls8 --bsr12 --lazy --ohh January 25, 2021 @ 09:06
14348 bytes -1 byte zopfli --i1000 --mls4 --bsr25 --lazy --ohh January 25, 2021 @ 09:06
14349 bytes -2 bytes zopfli --i1000 --mls4 --bsr23 --lazy --ohh January 25, 2021 @ 09:05
14351 bytes zopfli --i100 --mls4 --bsr9 --lazy --ohh January 25, 2021 @ 08:41

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

Most recent activity on January 28, 2021 @ 13:29.

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 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
14354 14354 14353 14353 14354 14355 14355 14357 14357 14355 14354 14362 14361 14366 14361
14350 14350 14353 14347 14346 14352 14352 14363 14354 14346 14346 14348 14348 14347 14359
14350 14348 14346 14349 14352 14348 14347 14365 14366 14346 14347 14349 14348 14344 14347
14354 14355 14346 14351 14352 14346 14352 14352 14352 14346 14349 14348 14348 14347 14344
14347 14354 14347 14346 14346 14355 14344 14347 14351 14351 14354 14348 14348 14347 14347
14346 14344 14346 14350 14352 14353 14352 14363 14344 14346 14356 14350 14348 14348 14344
14346 14344 14352 14352 14352 14353 14347 14350 14353 14352 14349 14348 14347 14347 14346
14350 14346 14352 14351 14353 14347 14347 14366 14346 14344 14349 14348 14348 14347 14347
14347 14344 14346 14346 14352 14354 14350 14366 14352 14344 14349 14349 14348 14347 14345
14350 14351 14346 14347 14352 14353 14352 14352 14351 14365 14347 14348 14348 14347 14347
14350 14344 14352 14346 14352 14347 14350 14362 14357 14346 14349 14348 14348 14347 14347
14350 14347 14346 14347 14346 14348 14352 14365 14351 14346 14347 14348 14346 14347 14347
14346 14344 14352 14346 14347 14352 14352 14366 14352 14347 14347 14348 14348 14346 14346
14351 14346 14347 14346 14346 14355 14352 14347 14365 14346 14347 14350 14349 14347 14347
14346 14347 14346 14346 14346 14351 14352 14351 14350 14346 14347 14349 14348 14347 14348
14349 14352 14352 14351 14346 14353 14347 14366 14365 14346 14347 14348 14348 14348 14348
14346 14352 14352 14349 14351 14346 14352 14352 14367 14346 14349 14349 14348 14347 14347
14347 14351 14346 14347 14346 14353 14346 14346 14353 14346 14349 14348 14348 14347 14347
14350 14353 14351 14351 14346 14353 14352 14367 14344 14366 14349 14349 14348 14347 14344
14350 14346 14346 14349 14346 14353 14352 14366 14346 14365 14349 14348 14348 14347 14347
14346 14344 14346 14351 14346 14353 14347 14352 14352 14366 14349 14349 14348 14347 14347
14350 14353 14352 14346 14346 14348 14352 14363 14351 14344 14349 14348 14348 14347 14347
14350 14353 14346 14347 14347 14354 14346 14352 14353 14346 14349 14349 14346 14348 14349

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 14351 bytes 100%
1,000 14346 bytes -5 bytes 100%
10,000 14345 bytes -1 byte 100%
100,000 14345 bytes 4.93%
1,000,000 14344 bytes -1 byte 4.93%
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
14418 bytes +74 bytes (+0.52%) +38 bytes
14418 bytes +74 bytes (+0.52%) +38 bytes
14380 bytes +36 bytes (+0.25%)
14399 bytes +55 bytes (+0.38%) +19 bytes
14390 bytes +46 bytes (+0.32%) +10 bytes
14412 bytes +68 bytes (+0.47%) +32 bytes
14420 bytes +76 bytes (+0.53%) +40 bytes
14461 bytes +117 bytes (+0.82%) +81 bytes
14498 bytes +154 bytes (+1.07%) +118 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 11654 bytes -2690 bytes (-18.75%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 12153 bytes -2191 bytes (-15.27%)
Brotli (Wikipedia) brotli brotli -q 11 13134 bytes -1210 bytes (-8.44%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 13629 bytes -715 bytes (-4.98%)
LZMA2 (Wikipedia) xz xz -9 13960 bytes -384 bytes (-2.68%)
Zstandard (Wikipedia) zstd zstd -19 14055 bytes -289 bytes (-2.01%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 14413 bytes +69 bytes (+0.48%)

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 2021.
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.