Choose a version:
46% The original file has 307814 bytes (300.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 142985 bytes (139.6k, 46%).

After GZIP compression these minified files vary in size:
Boot
  56013 bytes (54.7k)
CDN, direct link
Baidu
  48886 bytes (47.7k)
CDN, direct link
cdnjs
  48876 bytes (47.7k)
CDN, direct link
gzip -6 (default)
  48503 bytes (47.4k)
local copy
cdnhttps
  48464 bytes (47.3k)
CDN, direct link
unpkg
  48421 bytes (47.3k)
CDN, direct link
gzip -9
  48332 bytes (47.2k)
local copy
libdeflate -12
  46765 bytes (45.7k)
local copy
7zip -mx=9 -tgzip
  46759 bytes (45.7k)
local copy
pigz -11 -n
  46608 bytes (45.5k)
local copy
kzip -s0 -rn -b7
  46582 bytes (45.5k)
local copy
Zopfli
  46464 bytes (45.4k)
local copy
Zopfli (defluff)
  46461 bytes (45.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/d3/d3-3.2.1.min.js

You will automatically get the smallest D3 3.2.1 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 1957 bytes by using my D3 3.2.1 Zopfli version instead of the best available CDN (4.21% smaller than unpkg, 46464 vs. 48421 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 --mls64 --bsr12 --lazy --ohh

(found December 21, 2015)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 64  --mls64
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

Even Smaller Files Thanks To Defluff

Zopfli's output can be further optimized by the defluff tool.
In this particular case, defluff saves 3 more bytes (46461 bytes).

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/mbostock/d3/v3.2.1/d3.min.js --location | md5sum
369eb973d43684e0f447e22edabdbaad  -
curl --silent --compressed http://minime.stephan-brumme.com/files/d3/d3-3.2.1.min.zopfli.js.gz | md5sum
369eb973d43684e0f447e22edabdbaad  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/mbostock/d3/v3.2.1/d3.min.js --location | sha1sum
d7e870f321511ec471110122b79333b48e3c06ae  -
curl --silent --compressed http://minime.stephan-brumme.com/files/d3/d3-3.2.1.min.zopfli.js.gz | sha1sum
d7e870f321511ec471110122b79333b48e3c06ae  -

These CDNs send you the original file:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 56013 bytes 369eb973d43684e0f447e22edabdbaad (invalid)
cdnjs 48876 bytes 369eb973d43684e0f447e22edabdbaad (invalid)
cdnhttps 48464 bytes 369eb973d43684e0f447e22edabdbaad December 24, 2015 @ 07:33
unpkg 48421 bytes 369eb973d43684e0f447e22edabdbaad July 11, 2016 @ 16:32

And some CDNs send you a different file:
CDN Size (compressed) MD5 (uncompressed) Comment / Diff Timestamp
Baidu 48886 bytes 837e1971764d742447f081305c745e30 only whitespaces differ (invalid)

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

Other Versions

Available D3 versions at minime.stephan-brumme.com:

4.11.0, 4.10.2, 4.10.1, 4.10.0,
4.9.1, 4.9.0, 4.8.0, 4.7.4, 4.7.3, 4.7.2, 4.7.1, 4.7.0, 4.6.0, 4.5.0, 4.4.4, 4.4.3, 4.4.2, 4.4.1, 4.4.0, 4.3.0, 4.2.8, 4.2.7, 4.2.6, 4.2.5, 4.2.4, 4.2.3, 4.2.2, 4.2.1, 4.2.0, 4.1.1, 4.1.0, 4.0.0,
3.5.17, 3.5.16, 3.5.15, 3.5.14, 3.5.13, 3.5.12, 3.5.11, 3.5.10, 3.5.9, 3.5.8, 3.5.7, 3.5.6, 3.5.5, 3.5.4, 3.5.3, 3.5.2, 3.5.1, 3.5.0, 3.4.13, 3.4.12, 3.4.11, 3.4.10, 3.4.9, 3.4.8, 3.4.6, 3.4.5, 3.4.4, 3.4.3, 3.4.2, 3.4.1, 3.4.0, 3.3.13, 3.3.12, 3.3.11, 3.3.10, 3.3.9, 3.3.8, 3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.3, 3.3.2, 3.3.1, 3.3.0, 3.2.8, 3.2.7, 3.2.6, 3.2.5, 3.2.4, 3.2.3, 3.2.2, 3.2.1, 3.2.0, 3.1.10, 3.1.9, 3.1.8, 3.1.7, 3.1.6, 3.1.5, 3.1.4, 3.1.3, 3.1.2, 3.1.1, 3.1.0, 3.0.8, 3.0.7, 3.0.6, 3.0.5, 3.0.4, 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, Bootstrap, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
46464 bytes -4 bytes zopfli --i100000 --mls64 --bsr12 --lazy --ohh December 21, 2015 @ 15:47
46468 bytes -4 bytes zopfli --i10000 --mls64 --bsr12 --lazy --ohh November 23, 2015 @ 17:35
46472 bytes -10 bytes zopfli --i1000 --mls64 --bsr12 --lazy --ohh September 20, 2015 @ 06:28
46482 bytes zopfli --i100 --mls64 --bsr12 --lazy --ohh September 18, 2015 @ 19:44

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

Most recent activity on March 1, 2017 @ 00:34.

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 100,000.
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
46672 46679 46674 46616 46668 46568 46664 46668 46579 46673 46668 46697 46707 46695 46695
46604 46643 46614 46613 46508 46648 46604 46683 46689 46511 46698 46693 46695 46700 46678
46501 46562 46512 46498 46485 46512 46531 46566 46501 46494 46695 46572 46699 46563 46586
46497 46507 46529 46558 46542 46519 46520 46613 46544 46527 46526 46521 46698 46567 46527
46562 46509 46517 46512 46519 46509 46541 46625 46525 46490 46575 46575 46694 46582 46556
46520 46691 46517 46526 46500 46509 46521 46619 46632 46574 46661 46647 46681 46694 46520
46524 46510 46510 46507 46515 46496 46518 46648 46646 46644 46634 46644 46598 46557 46566
46501 46507 46537 46518 46490 46546 46521 46514 46509 46536 46514 46517 46675 46694 46506
46495 46538 46510 46518 46567 46464 46512 46649 46693 46478 46515 46502 46675 46571 46509
46518 46510 46513 46515 46539 46525 46571 46626 46513 46524 46548 46529 46695 46563 46565
46569 46558 46506 46514 46516 46589 46512 46623 46634 46506 46509 46527 46681 46563 46555
46518 46495 46528 46518 46522 46504 46502 46647 46634 46514 46640 46642 46675 46687 46671
46569 46568 46556 46504 46522 46517 46509 46629 46642 46655 46521 46687 46690 46557 46562
46568 46571 46527 46506 46522 46515 46590 46517 46693 46510 46527 46689 46672 46685 46549
46570 46559 46559 46516 46501 46514 46595 46631 46693 46516 46508 46687 46679 46566 46562
46504 46485 46585 46513 46564 46516 46519 46497 46671 46514 46519 46524 46683 46568 46562
46513 46513 46510 46505 46520 46520 46530 46649 46642 46478 46635 46649 46678 46563 46554
46521 46500 46522 46515 46534 46504 46532 46607 46641 46642 46634 46644 46622 46567 46540
46496 46511 46517 46510 46509 46528 46521 46612 46641 46486 46517 46519 46674 46563 46682
46507 46510 46518 46513 46510 46518 46594 46549 46517 46521 46515 46530 46698 46561 46612
46500 46509 46517 46513 46515 46540 46595 46645 46645 46506 46512 46646 46695 46564 46556
46515 46575 46519 46517 46504 46528 46605 46634 46624 46481 46521 46646 46697 46564 46572
46510 46512 46524 46519 46517 46503 46593 46514 46519 46511 46517 46518 46696 46564 46501

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 46482 bytes 100%
1,000 46472 bytes -10 bytes 100%
10,000 46468 bytes -4 bytes 100%
100,000 46464 bytes -4 bytes 0.29%
1,000,000
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
46702 bytes +238 bytes (+0.51%) +120 bytes
46715 bytes +251 bytes (+0.54%) +133 bytes
46702 bytes +238 bytes (+0.51%) +120 bytes
46658 bytes +194 bytes (+0.42%) +76 bytes
46675 bytes +211 bytes (+0.45%) +93 bytes
46678 bytes +214 bytes (+0.46%) +96 bytes
46638 bytes +174 bytes (+0.37%) +56 bytes
46582 bytes +118 bytes (+0.25%)
46606 bytes +142 bytes (+0.31%) +24 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
Algorithm Program Parameters Size Compared To Best Zopfli
ZPAQ (Wikipedia) zpaq zpaq -method 69 37339 bytes -9125 bytes (-19.64%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 39517 bytes -6947 bytes (-14.95%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 40153 bytes -6311 bytes (-13.58%)
Brotli (Wikipedia) brotli brotli -q 11 41997 bytes -4467 bytes (-9.61%)
LZMA2 (Wikipedia) xz xz -9 42812 bytes -3652 bytes (-7.86%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 44753 bytes -1711 bytes (-3.68%)
ZSTD (Wikipedia) zstd zstd -19 44864 bytes -1600 bytes (-3.44%)

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 2017.
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