Choose a version:
53% The original file has 70815 bytes (69.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 37608 bytes (36.7k, 53%).

After GZIP compression these minified files vary in size:
cdnjs
  10098 bytes (9.9k)
CDN
gzip -6 (default)
  10058 bytes (9.8k)
local copy
MaxCDN
  10035 bytes (9.8k)
CDN
gzip -9
  10019 bytes (9.8k)
local copy
unpkg
  10006 bytes (9.8k)
CDN
libdeflate -12
  9692 bytes (9.5k)
local copy
7zip -mx=9 -tgzip
  9690 bytes (9.5k)
local copy
kzip -s0 -rn -b2
  9690 bytes (9.5k)
local copy
pigz -11 -n
  9644 bytes (9.4k)
local copy
Zopfli
  9632 bytes (9.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.4.0.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 3.4.0 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 374 bytes by using my Bootstrap 3.4.0 Zopfli version instead of the best available CDN (3.88% smaller than unpkg, 9632 vs. 10006 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 --mls8192 --bsr11 --lazy --ohh

(found December 14, 2018)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 8192  --mls8192
block splitting recursion 11  --bsr11
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/v3.4.0/dist/js/bootstrap.min.js --location | md5sum
3d8308804264c5b751f6e54734c46897  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.4.0.min.zopfli.js.gz | md5sum
3d8308804264c5b751f6e54734c46897  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v3.4.0/dist/js/bootstrap.min.js --location | sha1sum
369a832ef7f8a57e9b59b84b181fdb4fc9125050  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.4.0.min.zopfli.js.gz | sha1sum
369a832ef7f8a57e9b59b84b181fdb4fc9125050  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
cdnjs 10098 bytes 3d8308804264c5b751f6e54734c46897 (invalid)
MaxCDN 10035 bytes 3d8308804264c5b751f6e54734c46897 (invalid)
unpkg 10006 bytes 3d8308804264c5b751f6e54734c46897 (invalid)

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

Other Versions

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

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
9632 bytes -1 byte zopfli --i1000000 --mls8192 --bsr11 --lazy --ohh December 14, 2018 @ 18:17
9633 bytes -1 byte zopfli --i10000 --mls8192 --bsr11 --lazy --ohh December 14, 2018 @ 14:20
9634 bytes -1 byte zopfli --i10000 --mls256 --bsr20 --lazy --ohh December 14, 2018 @ 14:18
9635 bytes zopfli --i100 --mls256 --bsr20 --lazy --ohh December 14, 2018 @ 13:57

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

Most recent activity on December 14, 2018 @ 18:19.

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
9644 9644 9644 9643 9643 9643 9638 9636 9638 9635 9634 9635 9641 9646 9644
9636 9636 9634 9637 9636 9635 9636 9634 9636 9636 9635 9637 9636 9637 9637
9638 9638 9638 9637 9636 9637 9635 9634 9635 9636 9636 9636 9635 9635 9635
9636 9636 9641 9642 9642 9637 9636 9634 9635 9636 9636 9637 9637 9636 9637
9636 9636 9634 9641 9637 9641 9636 9634 9635 9636 9636 9637 9636 9643 9636
9635 9634 9636 9637 9637 9635 9636 9634 9635 9635 9636 9638 9645 9635 9636
9636 9636 9637 9642 9635 9641 9641 9636 9636 9636 9634 9637 9637 9635 9636
9636 9636 9634 9642 9635 9636 9636 9634 9634 9636 9635 9637 9632 9637 9637
9636 9636 9634 9637 9637 9634 9636 9634 9636 9636 9636 9635 9636 9637 9637
9636 9636 9634 9637 9637 9636 9636 9634 9635 9636 9636 9637 9636 9637 9636
9636 9636 9634 9637 9636 9636 9636 9634 9637 9635 9637 9637 9637 9643 9636
9637 9637 9635 9636 9635 9636 9636 9637 9635 9636 9636 9635 9636 9636 9632
9636 9636 9634 9642 9635 9636 9636 9635 9635 9635 9637 9635 9636 9636 9635
9636 9636 9634 9637 9634 9632 9635 9635 9635 9636 9635 9635 9636 9637 9636
9636 9636 9634 9636 9642 9636 9636 9636 9636 9636 9636 9637 9636 9635 9636
9636 9636 9635 9641 9634 9636 9637 9634 9636 9636 9635 9637 9636 9643 9636
9636 9636 9636 9637 9635 9636 9635 9634 9637 9636 9635 9638 9636 9637 9635
9636 9636 9634 9637 9635 9635 9636 9636 9637 9636 9635 9638 9636 9637 9636
9636 9636 9634 9637 9635 9635 9636 9634 9637 9636 9635 9637 9636 9643 9632
9636 9636 9636 9641 9635 9634 9637 9636 9635 9636 9634 9637 9637 9637 9636
9636 9636 9634 9637 9635 9636 9636 9635 9637 9636 9634 9635 9636 9643 9635
9636 9636 9634 9636 9635 9636 9634 9634 9635 9636 9637 9637 9636 9641 9638
9637 9637 9634 9637 9635 9636 9636 9636 9637 9634 9635 9637 9640 9637 9636

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 9635 bytes 100%
1,000 9635 bytes 100%
10,000 9633 bytes -2 bytes 100%
100,000 9633 bytes 1.16%
1,000,000 9632 bytes -1 byte 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
9690 bytes +58 bytes (+0.60%)
9692 bytes +60 bytes (+0.62%) +2 bytes
9690 bytes +58 bytes (+0.60%)
9715 bytes +83 bytes (+0.86%) +25 bytes
9723 bytes +91 bytes (+0.94%) +33 bytes
9763 bytes +131 bytes (+1.36%) +73 bytes
9802 bytes +170 bytes (+1.76%) +112 bytes
9833 bytes +201 bytes (+2.09%) +143 bytes
9877 bytes +245 bytes (+2.54%) +187 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
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 8105 bytes -1527 bytes (-15.85%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 8763 bytes -869 bytes (-9.02%)
Brotli (Wikipedia) brotli brotli -q 11 8884 bytes -748 bytes (-7.77%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 9175 bytes -457 bytes (-4.74%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 9473 bytes -159 bytes (-1.65%)
LZMA2 (Wikipedia) xz xz -9 9568 bytes -64 bytes (-0.66%)
Zstandard (Wikipedia) zstd zstd -19 9582 bytes -50 bytes (-0.52%)

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