Choose a version:
32% The original file has 70852 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 22857 bytes (22.3k, 32%).

After GZIP compression these minified files vary in size:
Boot
  8671 bytes (8.5k)
CDN, direct link
cdnjs
  7466 bytes (7.3k)
CDN, direct link
gzip -6 (default)
  7441 bytes (7.3k)
local copy
gzip -9
  7432 bytes (7.3k)
local copy
unpkg
  7429 bytes (7.3k)
CDN, direct link
cdnhttps
  7419 bytes (7.2k)
CDN, direct link
jsdelivr
  7414 bytes (7.2k)
CDN, direct link
7zip -mx=9 -tgzip
  7221 bytes (7.1k)
local copy
libdeflate -12
  7210 bytes (7.0k)
local copy
pigz -11 -n
  7206 bytes (7.0k)
local copy
kzip -s0 -rn -b0
  7202 bytes (7.0k)
local copy
Zopfli
  7200 bytes (7.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/backbonejs/backbone-1.2.1.min.js

You will automatically get the smallest BackboneJS 1.2.1 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 214 bytes by using my BackboneJS 1.2.1 Zopfli version instead of the best available CDN (2.97% smaller than jsdelivr, 7200 vs. 7414 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 --i10000 --mb8 --mls2048 --bsr13 --lazy --ohh

(found September 8, 2015)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 2048  --mls2048
block splitting recursion 13  --bsr13
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/1.2.1/backbone-min.js --location | md5sum
1671918bffa92a85d3caaf2a2bd24e7a  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-1.2.1.min.zopfli.js.gz | md5sum
1671918bffa92a85d3caaf2a2bd24e7a  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/backbone/1.2.1/backbone-min.js --location | sha1sum
f745a8455c6355a24decf31b6c6c2c1dd42f0466  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-1.2.1.min.zopfli.js.gz | sha1sum
f745a8455c6355a24decf31b6c6c2c1dd42f0466  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 8671 bytes 1671918bffa92a85d3caaf2a2bd24e7a (invalid)
cdnjs 7466 bytes 1671918bffa92a85d3caaf2a2bd24e7a (invalid)
unpkg 7429 bytes 1671918bffa92a85d3caaf2a2bd24e7a July 11, 2016 @ 16:18
cdnhttps 7419 bytes 1671918bffa92a85d3caaf2a2bd24e7a December 24, 2015 @ 07:32
jsdelivr 7414 bytes 1671918bffa92a85d3caaf2a2bd24e7a (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
7200 bytes -1 byte zopfli --i10000 --mls2048 --bsr13 --lazy --ohh September 8, 2015 @ 12:24
7201 bytes -1 byte zopfli --i1000 --mls512 --bsr9 --lazy --ohh September 8, 2015 @ 11:39
7202 bytes zopfli --i100 --mls512 --bsr14 --lazy --ohh September 8, 2015 @ 11:32

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

Most recent activity on July 11, 2016 @ 16:18.

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 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
7204 7203 7203 7203 7203 7204 7204 7204 7202 7204 7204 7202 7201 7202 7201
7202 7202 7201 7202 7202 7203 7202 7202 7202 7203 7201 7203 7203 7203 7203
7203 7202 7203 7210 7201 7210 7204 7210 7203 7201 7204 7203 7202 7202 7201
7210 7201 7211 7212 7205 7203 7204 7209 7202 7207 7202 7204 7202 7203 7203
7203 7204 7202 7202 7201 7203 7204 7201 7201 7203 7201 7204 7202 7203 7203
7211 7202 7202 7202 7202 7211 7202 7210 7200 7201 7201 7203 7203 7203 7203
7203 7202 7202 7200 7201 7202 7203 7211 7201 7201 7201 7204 7202 7203 7201
7203 7203 7203 7200 7201 7203 7203 7204 7200 7201 7201 7204 7203 7203 7203
7202 7202 7211 7201 7202 7203 7202 7201 7200 7200 7201 7203 7202 7203 7203
7202 7202 7202 7202 7201 7203 7202 7201 7201 7200 7200 7204 7202 7203 7203
7202 7202 7203 7200 7201 7202 7202 7201 7201 7200 7201 7203 7203 7203 7203
7202 7202 7212 7210 7202 7203 7203 7201 7201 7202 7202 7205 7202 7203 7203
7210 7202 7203 7201 7202 7202 7202 7201 7204 7201 7201 7204 7202 7203 7203
7202 7202 7202 7201 7203 7203 7203 7201 7201 7202 7202 7205 7202 7203 7203
7202 7202 7203 7201 7202 7201 7202 7201 7202 7202 7201 7205 7203 7203 7203
7202 7202 7202 7201 7202 7201 7210 7210 7201 7202 7201 7204 7203 7203 7203
7202 7202 7202 7202 7201 7201 7202 7201 7201 7203 7201 7204 7203 7203 7203
7202 7202 7202 7202 7201 7202 7203 7201 7202 7206 7200 7207 7203 7203 7203
7201 7210 7211 7210 7201 7203 7210 7211 7201 7201 7202 7205 7203 7203 7203
7200 7203 7202 7201 7201 7203 7203 7201 7201 7201 7200 7204 7203 7203 7203
7202 7202 7211 7201 7202 7203 7203 7211 7201 7201 7200 7204 7203 7203 7203
7203 7201 7200 7202 7202 7203 7202 7202 7201 7201 7202 7205 7203 7203 7203
7202 7203 7203 7201 7201 7202 7203 7201 7201 7202 7202 7205 7202 7203 7203

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 7202 bytes 100%
1,000 7201 bytes -1 byte 100%
10,000 7200 bytes -1 byte 100%
100,000 7200 bytes 18.55%
1,000,000 7200 bytes 0.29%
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
7202 bytes +2 bytes (+0.03%)
7202 bytes +2 bytes (+0.03%)
7232 bytes +32 bytes (+0.44%) +30 bytes
7261 bytes +61 bytes (+0.85%) +59 bytes
7300 bytes +100 bytes (+1.39%) +98 bytes
7314 bytes +114 bytes (+1.58%) +112 bytes
7330 bytes +130 bytes (+1.81%) +128 bytes
7361 bytes +161 bytes (+2.24%) +159 bytes
7389 bytes +189 bytes (+2.63%) +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.
Algorithm Program Parameters Size Compared To Best Zopfli
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 6275 bytes -925 bytes (-12.85%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6738 bytes -462 bytes (-6.42%)
Brotli (Wikipedia) brotli brotli -q 11 6743 bytes -457 bytes (-6.35%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 6901 bytes -299 bytes (-4.15%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7127 bytes -73 bytes (-1.01%)
ZSTD (Wikipedia) zstd zstd -19 7193 bytes -7 bytes (-0.10%)
LZMA2 (Wikipedia) xz xz -9 7224 bytes +24 bytes (+0.33%)

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