Choose a version:
32% The original file has 72164 bytes (70.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 23314 bytes (22.8k, 32%).

After GZIP compression these minified files vary in size:
Boot
  8804 bytes (8.6k)
CDN, direct link
cdnjs
  7585 bytes (7.4k)
CDN, direct link
gzip -6 (default)
  7567 bytes (7.4k)
local copy
gzip -9
  7559 bytes (7.4k)
local copy
cdnhttps
  7545 bytes (7.4k)
CDN, direct link
unpkg
  7545 bytes (7.4k)
CDN, direct link
jsdelivr
  7541 bytes (7.4k)
CDN, direct link
pigz -11 -n
  7328 bytes (7.2k)
local copy
libdeflate -12
  7324 bytes (7.2k)
local copy
7zip -mx=9 -tgzip
  7322 bytes (7.2k)
local copy
kzip -s0 -rn -b0
  7318 bytes (7.1k)
local copy
Zopfli
  7318 bytes (7.1k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/backbonejs/backbone-1.3.1.min.js

You will automatically get the smallest BackboneJS 1.3.1 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 223 bytes by using my BackboneJS 1.3.1 Zopfli version instead of the best available CDN (3.05% smaller than jsdelivr, 7318 vs. 7541 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 --mls2 --bsr14 --lazy --ohh

(found March 6, 2016)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 2  --mls2
block splitting recursion 14  --bsr14
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/jashkenas/backbone/1.3.1/backbone-min.js --location | md5sum
f07a47de25413196efc65820e53cb0af  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-1.3.1.min.zopfli.js.gz | md5sum
f07a47de25413196efc65820e53cb0af  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/backbone/1.3.1/backbone-min.js --location | sha1sum
10e90b5a5b1f765759b41e87b708f7a65dd41b31  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-1.3.1.min.zopfli.js.gz | sha1sum
10e90b5a5b1f765759b41e87b708f7a65dd41b31  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 8804 bytes f07a47de25413196efc65820e53cb0af March 7, 2016 @ 16:37
cdnjs 7585 bytes f07a47de25413196efc65820e53cb0af (invalid)
cdnhttps 7545 bytes f07a47de25413196efc65820e53cb0af November 22, 2016 @ 16:29
unpkg 7545 bytes f07a47de25413196efc65820e53cb0af July 11, 2016 @ 16:17
jsdelivr 7541 bytes f07a47de25413196efc65820e53cb0af (invalid)

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

Other Versions

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

1.3.3, 1.3.2, 1.3.1, 1.3.0,
1.2.3, 1.2.2, 1.2.1, 1.2.0,
1.1.2, 1.1.1, 1.1.0,
1.0.0,
0.9.10, 0.9.9, 0.9.2, 0.9.1, 0.9.0,
0.3.3, 0.3.2, 0.3.1, 0.3.0,
0.2.0,
0.1.2, 0.1.1

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

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
7318 bytes -1 byte zopfli --i1000000 --mls2 --bsr14 --lazy --ohh March 6, 2016 @ 19:57
7319 bytes -1 byte zopfli --i10000 --mls2 --bsr14 --lazy --ohh March 5, 2016 @ 09:58
7320 bytes -1 byte zopfli --i1000 --mls512 --bsr20 --lazy --ohh March 5, 2016 @ 09:48
7321 bytes zopfli --i100 --mls256 --bsr13 --lazy --ohh March 5, 2016 @ 09:41

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

Most recent activity on November 22, 2016 @ 16:29.

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, 100,000, 1,000,000 or 10,000,000.
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
7319 7319 7319 7319 7319 7318 7319 7319 7320 7320 7320 7323 7322 7322 7322
7327 7323 7327 7327 7322 7322 7321 7323 7324 7323 7322 7323 7322 7324 7325
7319 7323 7322 7323 7321 7319 7322 7323 7324 7322 7322 7321 7322 7323 7323
7321 7322 7321 7323 7321 7319 7321 7323 7323 7321 7321 7321 7326 7322 7325
7322 7323 7322 7323 7323 7319 7322 7322 7323 7321 7321 7321 7322 7322 7325
7318 7323 7322 7321 7322 7319 7321 7323 7323 7322 7321 7322 7323 7322 7321
7321 7323 7319 7320 7321 7320 7321 7323 7324 7321 7322 7321 7322 7321 7322
7319 7323 7322 7323 7321 7322 7319 7320 7323 7320 7321 7322 7322 7322 7322
7322 7323 7322 7323 7323 7323 7322 7323 7324 7321 7322 7321 7323 7321 7322
7322 7322 7322 7323 7323 7319 7321 7319 7323 7321 7321 7321 7321 7323 7323
7318 7323 7321 7319 7322 7319 7322 7323 7323 7320 7321 7321 7323 7321 7323
7321 7323 7321 7323 7323 7319 7322 7323 7323 7321 7321 7321 7320 7325 7325
7322 7322 7321 7323 7323 7319 7321 7322 7323 7322 7322 7321 7323 7323 7323
7321 7323 7322 7323 7323 7319 7321 7323 7323 7321 7321 7321 7322 7322 7322
7322 7323 7323 7320 7322 7319 7320 7323 7323 7322 7321 7322 7322 7321 7321
7319 7323 7322 7323 7323 7319 7321 7323 7321 7322 7322 7321 7323 7322 7324
7323 7323 7323 7323 7323 7320 7321 7323 7319 7322 7322 7322 7321 7322 7322
7318 7323 7323 7323 7321 7319 7321 7323 7323 7322 7321 7323 7322 7323 7323
7322 7322 7322 7323 7323 7320 7320 7323 7323 7322 7321 7322 7322 7321 7321
7318 7323 7322 7323 7319 7319 7321 7323 7323 7321 7322 7322 7322 7322 7322
7318 7323 7322 7323 7321 7320 7321 7323 7321 7321 7322 7321 7322 7322 7325
7321 7322 7322 7323 7323 7319 7321 7323 7323 7322 7322 7321 7322 7323 7323
7322 7323 7321 7324 7322 7319 7321 7323 7323 7322 7322 7321 7322 7321 7321

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 7321 bytes 100%
1,000 7320 bytes -1 byte 100%
10,000 7319 bytes -1 byte 100%
100,000 7319 bytes 13.91%
1,000,000 7318 bytes -1 byte 10.72%
10,000,000 7318 bytes 0.29%

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
7318 bytes – (0.00%)
7318 bytes – (0.00%)
7341 bytes +23 bytes (+0.31%) +23 bytes
7368 bytes +50 bytes (+0.68%) +50 bytes
7397 bytes +79 bytes (+1.08%) +79 bytes
7416 bytes +98 bytes (+1.34%) +98 bytes
7458 bytes +140 bytes (+1.91%) +140 bytes
7488 bytes +170 bytes (+2.32%) +170 bytes
7511 bytes +193 bytes (+2.64%) +193 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
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 6357 bytes -961 bytes (-13.13%)
Brotli (Wikipedia) brotli brotli -q 11 6840 bytes -478 bytes (-6.53%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6889 bytes -429 bytes (-5.86%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 6993 bytes -325 bytes (-4.44%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7216 bytes -102 bytes (-1.39%)
ZSTD (Wikipedia) zstd zstd -19 7309 bytes -9 bytes (-0.12%)
LZMA2 (Wikipedia) xz xz -9 7336 bytes +18 bytes (+0.25%)

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