Choose a version:
47% The original file has 293165 bytes (286.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 137383 bytes (134.2k, 47%).

After GZIP compression these minified files vary in size:
Boot
  53598 bytes (52.3k)
CDN, direct link
Baidu
  46739 bytes (45.6k)
CDN, direct link
cdnjs
  46728 bytes (45.6k)
CDN, direct link
gzip -6 (default)
  46428 bytes (45.3k)
local copy
cdnhttps
  46386 bytes (45.3k)
CDN, direct link
unpkg
  46302 bytes (45.2k)
CDN, direct link
gzip -9
  46247 bytes (45.2k)
local copy
7zip -mx=9 -tgzip
  44738 bytes (43.7k)
local copy
libdeflate -12
  44722 bytes (43.7k)
local copy
kzip -s0 -rn -b8
  44652 bytes (43.6k)
local copy
pigz -11 -n
  44554 bytes (43.5k)
local copy
Zopfli
  44446 bytes (43.4k)
local copy
Zopfli (defluff)
  44445 bytes (43.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/d3/d3-3.1.5.min.js

You will automatically get the smallest D3 3.1.5 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 1856 bytes by using my D3 3.1.5 Zopfli version instead of the best available CDN (4.18% smaller than unpkg, 44446 vs. 46302 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 --mls1024 --bsr11 --lazy --ohh

(found December 21, 2015)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 1024  --mls1024
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

Even Smaller Files Thanks To Defluff

Zopfli's output can be further optimized by the defluff tool.
In this particular case, defluff saves 1 more byte (44445 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/v3.1.5/d3.min.js --location | md5sum
124e3c925f1641f1346d86194211cb9f  -
curl --silent --compressed http://minime.stephan-brumme.com/files/d3/d3-3.1.5.min.zopfli.js.gz | md5sum
124e3c925f1641f1346d86194211cb9f  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/mbostock/d3/v3.1.5/d3.min.js --location | sha1sum
5f45c24309cb5b0a874f65fddee39904e9b8a0ff  -
curl --silent --compressed http://minime.stephan-brumme.com/files/d3/d3-3.1.5.min.zopfli.js.gz | sha1sum
5f45c24309cb5b0a874f65fddee39904e9b8a0ff  -

These CDNs send you the original file:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 53598 bytes 124e3c925f1641f1346d86194211cb9f (invalid)
cdnjs 46728 bytes 124e3c925f1641f1346d86194211cb9f (invalid)
cdnhttps 46386 bytes 124e3c925f1641f1346d86194211cb9f December 24, 2015 @ 07:33
unpkg 46302 bytes 124e3c925f1641f1346d86194211cb9f July 11, 2016 @ 16:32

And some CDNs send you a different file:
CDN Size (compressed) MD5 (uncompressed) Comment / Diff Timestamp
Baidu 46739 bytes 77aea7b6b9dfe66b240da049df5aab9f 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
44446 bytes -5 bytes zopfli --i100000 --mls1024 --bsr11 --lazy --ohh December 21, 2015 @ 13:38
44451 bytes -5 bytes zopfli --i10000 --mls1024 --bsr11 --lazy --ohh November 23, 2015 @ 17:18
44456 bytes -10 bytes zopfli --i1000 --mls256 --bsr10 --lazy --ohh September 20, 2015 @ 11:53
44466 bytes zopfli --i100 --mls1024 --bsr11 --lazy --ohh September 18, 2015 @ 21:37

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

Most recent activity on March 3, 2017 @ 10:00.

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
44629 44638 44631 44629 44623 44566 44616 44630 44650 44620 44636 44645 44659 44646 44641
44602 44603 44629 44572 44559 44511 44507 44514 44656 44542 44512 44546 44656 44639 44660
44522 44526 44529 44516 44504 44515 44484 44485 44545 44508 44528 44563 44652 44650 44650
44524 44523 44527 44515 44586 44516 44490 44532 44477 44473 44520 44494 44651 44651 44640
44533 44554 44520 44529 44518 44520 44532 44553 44516 44479 44544 44524 44658 44657 44656
44533 44524 44521 44533 44511 44510 44537 44495 44571 44474 44470 44623 44648 44647 44660
44542 44525 44530 44527 44546 44521 44466 44447 44584 44491 44483 44483 44644 44532 44608
44524 44521 44522 44541 44524 44517 44524 44570 44499 44446 44491 44491 44651 44544 44652
44544 44541 44531 44566 44531 44510 44537 44539 44528 44510 44511 44463 44625 44542 44660
44529 44513 44536 44547 44512 44522 44533 44536 44548 44478 44483 44486 44646 44640 44612
44537 44527 44528 44527 44513 44519 44498 44524 44583 44484 44507 44490 44646 44654 44652
44630 44516 44521 44614 44509 44459 44519 44521 44595 44495 44518 44480 44649 44649 44655
44540 44522 44528 44518 44522 44512 44532 44515 44646 44464 44534 44492 44648 44543 44651
44528 44515 44542 44522 44534 44517 44524 44640 44646 44492 44521 44652 44650 44649 44658
44541 44525 44527 44513 44511 44511 44539 44469 44646 44484 44478 44487 44646 44538 44654
44625 44629 44617 44544 44625 44513 44500 44492 44575 44470 44517 44483 44646 44638 44658
44540 44524 44524 44515 44511 44514 44530 44493 44547 44498 44485 44581 44646 44533 44646
44542 44512 44522 44543 44550 44511 44500 44495 44582 44487 44475 44488 44646 44645 44651
44633 44623 44629 44529 44541 44513 44535 44538 44487 44460 44476 44630 44655 44532 44653
44537 44512 44521 44545 44516 44520 44533 44540 44653 44487 44473 44483 44653 44533 44651
44536 44525 44562 44525 44517 44518 44508 44491 44583 44477 44518 44599 44650 44535 44651
44534 44512 44520 44516 44517 44514 44504 44518 44580 44477 44484 44482 44649 44529 44651
44539 44516 44532 44522 44516 44511 44527 44538 44466 44469 44627 44477 44646 44529 44652

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 44466 bytes 100%
1,000 44456 bytes -10 bytes 100%
10,000 44451 bytes -5 bytes 100%
100,000 44446 bytes -5 bytes 0.58%
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
44667 bytes +221 bytes (+0.50%) +15 bytes
44676 bytes +230 bytes (+0.52%) +24 bytes
44672 bytes +226 bytes (+0.51%) +20 bytes
44683 bytes +237 bytes (+0.53%) +31 bytes
44714 bytes +268 bytes (+0.60%) +62 bytes
44727 bytes +281 bytes (+0.63%) +75 bytes
44706 bytes +260 bytes (+0.58%) +54 bytes
44652 bytes +206 bytes (+0.46%)
44652 bytes +206 bytes (+0.46%)

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 35696 bytes -8750 bytes (-19.69%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 37784 bytes -6662 bytes (-14.99%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 38323 bytes -6123 bytes (-13.78%)
Brotli (Wikipedia) brotli brotli -q 11 40283 bytes -4163 bytes (-9.37%)
LZMA2 (Wikipedia) xz xz -9 40992 bytes -3454 bytes (-7.77%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 42712 bytes -1734 bytes (-3.90%)
ZSTD (Wikipedia) zstd zstd -19 42927 bytes -1519 bytes (-3.42%)

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