Choose a version:
32% The original file has 49275 bytes (48.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 15922 bytes (15.5k, 32%).

After GZIP compression these minified files vary in size:
jsdelivr
  6546 bytes (6.4k)
CDN, direct link
Boot
  6319 bytes (6.2k)
CDN, direct link
Baidu
  5608 bytes (5.5k)
CDN, direct link
cdnjs
  5587 bytes (5.5k)
CDN, direct link
gzip -6 (default)
  5575 bytes (5.4k)
local copy
gzip -9
  5572 bytes (5.4k)
local copy
unpkg
  5556 bytes (5.4k)
CDN, direct link
cdnhttps
  5553 bytes (5.4k)
CDN, direct link
libdeflate -12
  5419 bytes (5.3k)
local copy
7zip -mx=9 -tgzip
  5418 bytes (5.3k)
local copy
kzip -s0 -rn -b1
  5415 bytes (5.3k)
local copy
pigz -11 -n
  5413 bytes (5.3k)
local copy
Zopfli
  5408 bytes (5.3k)
local copy
Zopfli (defluff)
  5407 bytes (5.3k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/backbonejs/backbone-0.9.1.min.js

You will automatically get the smallest BackboneJS 0.9.1 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 145 bytes by using my BackboneJS 0.9.1 Zopfli version instead of the best available CDN (2.68% smaller than cdnhttps, 5408 vs. 5553 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 --mls1024 --bsr14 --lazy --ohh

(found November 27, 2015)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 1024  --mls1024
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

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 (5407 bytes).

Verify file integrity

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

MD5:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/backbone/0.9.1/backbone-min.js --location | md5sum
6291d846b4058bd9e2f962c53288af87  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-0.9.1.min.zopfli.js.gz | md5sum
6291d846b4058bd9e2f962c53288af87  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/backbone/0.9.1/backbone-min.js --location | sha1sum
dff93cf89bba4d3869f9805d1c0af9d97260afdd  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-0.9.1.min.zopfli.js.gz | sha1sum
dff93cf89bba4d3869f9805d1c0af9d97260afdd  -

These CDNs send you the original file:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Boot 6319 bytes 6291d846b4058bd9e2f962c53288af87 (invalid)
cdnjs 5587 bytes 6291d846b4058bd9e2f962c53288af87 (invalid)
unpkg 5556 bytes 6291d846b4058bd9e2f962c53288af87 July 11, 2016 @ 16:18
cdnhttps 5553 bytes 6291d846b4058bd9e2f962c53288af87 December 24, 2015 @ 07:32

And some CDNs send you a different file:
CDN Size (compressed) MD5 (uncompressed) Comment / Diff Timestamp
jsdelivr 6546 bytes c0f61ccea82807ce535917b48b6baa6d < // Backbone.js 0.9.1
> // Backbone.js 0.9.10
< (function(){var i=this,r=i.Backbone,s=Array.prototype.slic [...]
< {});var f=d.tail||(d.tail=d.next={});f.callback=b;f.contex [...]
< event:b}),(c=d[b])&&a.push({next:c.next,tail:c.tail});for( [...]
< {silent:!0}))throw Error("Can't create an invalid model"); [...]
< this.attributes[a]},set:function(a,b,c){var d,e;f.isObject [...]
< a,this._changing&&!f.isEqual(this._changed[e],a)&&(this.tr [...]
< e,f){if(!b.set(b.parse(d,f),a))return!1;c&&c(b,d)};a.error [...]
< k,c);b=this.isNew()?"create":"update";b=(this.sync||g.sync [...]
[...]
(invalid)
Baidu 5608 bytes be4f09a44ff38325e673eaf87e09bb60 only whitespaces differ (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
5408 bytes -1 byte zopfli --i1000000 --mls1024 --bsr14 --lazy --ohh November 27, 2015 @ 14:41
5409 bytes -1 byte zopfli --i1000 --mls1024 --bsr14 --lazy --ohh September 8, 2015 @ 11:48
5410 bytes zopfli --i100 --mls512 --bsr11 --lazy --ohh September 8, 2015 @ 11:31

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 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
5415 5415 5415 5415 5415 5415 5415 5415 5413 5415 5416 5411 5412 5412 5412
5413 5413 5415 5415 5415 5414 5415 5415 5415 5414 5416 5410 5417 5410 5410
5412 5412 5413 5413 5411 5411 5415 5418 5409 5410 5416 5409 5409 5409 5409
5410 5410 5415 5415 5411 5411 5411 5415 5411 5410 5416 5409 5409 5411 5411
5415 5415 5415 5415 5411 5411 5410 5416 5409 5410 5416 5411 5412 5411 5411
5413 5413 5412 5412 5411 5412 5410 5417 5409 5410 5416 5409 5409 5409 5409
5412 5412 5412 5412 5411 5411 5411 5418 5409 5410 5416 5409 5409 5409 5409
5409 5409 5412 5413 5410 5411 5410 5415 5409 5410 5416 5409 5410 5412 5412
5410 5410 5413 5415 5411 5411 5410 5415 5409 5410 5416 5409 5410 5409 5409
5412 5412 5409 5415 5411 5411 5411 5412 5410 5411 5416 5409 5410 5410 5410
5412 5412 5411 5415 5411 5411 5410 5412 5409 5408 5416 5409 5409 5411 5411
5413 5413 5411 5415 5411 5411 5410 5412 5409 5410 5416 5409 5409 5411 5411
5410 5410 5415 5415 5415 5411 5410 5417 5409 5410 5416 5409 5416 5409 5409
5412 5412 5411 5415 5411 5411 5410 5416 5409 5410 5416 5410 5411 5411 5411
5410 5410 5413 5413 5410 5411 5410 5416 5409 5410 5416 5409 5409 5409 5409
5413 5413 5409 5413 5411 5411 5410 5412 5409 5410 5416 5409 5409 5411 5411
5411 5411 5412 5412 5411 5411 5415 5417 5410 5410 5416 5411 5409 5409 5409
5415 5415 5410 5415 5415 5411 5415 5417 5409 5410 5416 5410 5410 5412 5412
5410 5410 5412 5412 5409 5411 5410 5411 5409 5410 5416 5409 5409 5411 5411
5410 5410 5411 5415 5411 5411 5410 5417 5409 5410 5416 5409 5409 5409 5409
5410 5410 5413 5412 5415 5411 5415 5416 5409 5409 5416 5409 5409 5411 5411
5409 5409 5412 5415 5415 5417 5415 5417 5411 5410 5416 5410 5409 5412 5412
5410 5410 5412 5413 5409 5411 5410 5416 5410 5410 5416 5409 5409 5409 5409

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 5410 bytes 100%
1,000 5409 bytes -1 byte 100%
10,000 5409 bytes 100%
100,000 5409 bytes 0.29%
1,000,000 5408 bytes -1 byte 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
5415 bytes +7 bytes (+0.13%)
5415 bytes +7 bytes (+0.13%)
5444 bytes +36 bytes (+0.67%) +29 bytes
5478 bytes +70 bytes (+1.29%) +63 bytes
5493 bytes +85 bytes (+1.57%) +78 bytes
5536 bytes +128 bytes (+2.37%) +121 bytes
5574 bytes +166 bytes (+3.07%) +159 bytes
5600 bytes +192 bytes (+3.55%) +185 bytes
5635 bytes +227 bytes (+4.20%) +220 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 4776 bytes -632 bytes (-11.69%)
Brotli (Wikipedia) brotli brotli -q 11 4945 bytes -463 bytes (-8.56%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 5423 bytes +15 bytes (+0.28%)
ZSTD (Wikipedia) zstd zstd -19 5445 bytes +37 bytes (+0.68%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 5460 bytes +52 bytes (+0.96%)
LZMA2 (Wikipedia) xz xz -9 5504 bytes +96 bytes (+1.78%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 5585 bytes +177 bytes (+3.27%)

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