Choose a version:
32% The original file has 71415 bytes (69.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 23097 bytes (22.6k, 32%).

After GZIP compression these minified files vary in size:
Boot
  8733 bytes (8.5k)
CDN, direct link
cdnjs
  7536 bytes (7.4k)
CDN, direct link
gzip -6 (default)
  7511 bytes (7.3k)
local copy
gzip -9
  7504 bytes (7.3k)
local copy
fastcdn
  7499 bytes (7.3k)
CDN, direct link
unpkg
  7499 bytes (7.3k)
CDN, direct link
cdnhttps
  7489 bytes (7.3k)
CDN, direct link
Yandex
  7486 bytes (7.3k)
CDN, direct link
jsdelivr
  7486 bytes (7.3k)
CDN, direct link
libdeflate -12
  7304 bytes (7.1k)
local copy
pigz -11 -n
  7278 bytes (7.1k)
local copy
7zip -mx=9 -tgzip
  7273 bytes (7.1k)
local copy
Zopfli
  7267 bytes (7.1k)
local copy
kzip -s0 -rn -b0
  7265 bytes (7.1k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/backbonejs/backbone-1.2.3.min.js

You will automatically get the smallest BackboneJS 1.2.3 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 219 bytes by using my BackboneJS 1.2.3 Zopfli version instead of the best available CDN (3.01% smaller than jsdelivr, 7267 vs. 7486 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 --bsr8 --lazy --ohh

(found September 8, 2015)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 1024  --mls1024
block splitting recursion 8  --bsr8
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/1.2.3/backbone-min.js --location | md5sum
bac416c324a009ab62240b20609ee313  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-1.2.3.min.zopfli.js.gz | md5sum
bac416c324a009ab62240b20609ee313  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/backbone/1.2.3/backbone-min.js --location | sha1sum
124b4a2c0a3b18702a52afbda1eb6da40bececd5  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-1.2.3.min.zopfli.js.gz | sha1sum
124b4a2c0a3b18702a52afbda1eb6da40bececd5  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 8733 bytes bac416c324a009ab62240b20609ee313 (invalid)
cdnjs 7536 bytes bac416c324a009ab62240b20609ee313 (invalid)
fastcdn 7499 bytes bac416c324a009ab62240b20609ee313 (invalid)
unpkg 7499 bytes bac416c324a009ab62240b20609ee313 July 11, 2016 @ 16:18
cdnhttps 7489 bytes bac416c324a009ab62240b20609ee313 (invalid)
Yandex 7486 bytes bac416c324a009ab62240b20609ee313 (invalid)
jsdelivr 7486 bytes bac416c324a009ab62240b20609ee313 (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
7267 bytes -1 byte zopfli --i100000 --mls1024 --bsr8 --lazy --ohh September 8, 2015 @ 18:08
7268 bytes -1 byte zopfli --i10000 --mls512 --bsr2 --lazy --ohh September 8, 2015 @ 11:53
7269 bytes zopfli --i100 --mls512 --bsr2 --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:
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
7269 7268 7268 7268 7268 7273 7268 7278 7268 7268 7270 7269 7269 7268 7268
7268 7268 7274 7276 7275 7269 7273 7275 7276 7271 7269 7269 7270 7271 7270
7270 7270 7268 7267 7268 7275 7269 7275 7271 7270 7270 7269 7270 7270 7270
7268 7268 7268 7269 7275 7275 7270 7274 7269 7271 7268 7269 7269 7270 7270
7268 7269 7268 7270 7271 7277 7268 7278 7269 7267 7268 7269 7268 7271 7271
7268 7269 7268 7270 7271 7268 7269 7269 7270 7270 7270 7268 7271 7271 7271
7267 7269 7268 7268 7275 7268 7269 7267 7269 7271 7268 7268 7268 7270 7270
7268 7270 7268 7269 7270 7271 7272 7267 7269 7271 7268 7269 7271 7271 7270
7268 7269 7273 7269 7274 7275 7273 7274 7271 7271 7269 7268 7271 7270 7271
7268 7269 7268 7269 7274 7275 7268 7273 7271 7271 7268 7269 7271 7271 7271
7269 7268 7268 7269 7268 7271 7268 7268 7271 7270 7269 7269 7270 7270 7270
7267 7268 7268 7268 7275 7275 7269 7274 7270 7271 7270 7269 7270 7271 7270
7268 7271 7281 7268 7269 7271 7268 7267 7271 7270 7270 7268 7271 7270 7271
7268 7269 7267 7269 7268 7275 7268 7274 7271 7271 7268 7269 7268 7271 7272
7268 7269 7280 7269 7268 7268 7268 7271 7270 7271 7268 7268 7269 7271 7270
7268 7268 7268 7270 7269 7271 7269 7269 7270 7271 7269 7270 7270 7271 7270
7268 7269 7269 7270 7270 7275 7268 7269 7269 7270 7269 7268 7270 7270 7270
7268 7268 7268 7269 7269 7269 7268 7269 7268 7271 7270 7268 7269 7271 7271
7268 7270 7268 7269 7269 7275 7268 7274 7271 7271 7268 7269 7269 7271 7271
7268 7268 7268 7269 7269 7275 7268 7269 7269 7270 7268 7268 7271 7271 7271
7268 7269 7268 7271 7270 7268 7268 7273 7269 7271 7268 7268 7269 7271 7271
7267 7269 7267 7278 7275 7268 7268 7268 7270 7271 7269 7269 7269 7270 7268
7268 7271 7268 7269 7275 7275 7269 7275 7269 7271 7269 7268 7271 7271 7271

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 7269 bytes 100%
1,000 7268 bytes -1 byte 100%
10,000 7268 bytes 100%
100,000 7267 bytes -1 byte 100%
1,000,000 7267 bytes 7.83%
10,000,000 7267 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
7265 bytes -2 bytes (-0.03%)
7265 bytes -2 bytes (-0.03%)
7298 bytes +31 bytes (+0.43%) +33 bytes
7340 bytes +73 bytes (+1.00%) +75 bytes
7353 bytes +86 bytes (+1.18%) +88 bytes
7381 bytes +114 bytes (+1.57%) +116 bytes
7412 bytes +145 bytes (+2.00%) +147 bytes
7427 bytes +160 bytes (+2.20%) +162 bytes
7458 bytes +191 bytes (+2.63%) +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 6303 bytes -964 bytes (-13.27%)
Brotli (Wikipedia) brotli brotli -q 11 6796 bytes -471 bytes (-6.48%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6808 bytes -459 bytes (-6.32%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 6940 bytes -327 bytes (-4.50%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7169 bytes -98 bytes (-1.35%)
ZSTD (Wikipedia) zstd zstd -19 7257 bytes -10 bytes (-0.14%)
LZMA2 (Wikipedia) xz xz -9 7284 bytes +17 bytes (+0.23%)

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