Choose a version:
32% The original file has 33956 bytes (33.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 10958 bytes (10.7k, 32%).

After GZIP compression these minified files vary in size:
Boot
  4214 bytes (4.1k)
CDN, direct link
gzip -6 (default)
  3756 bytes (3.7k)
local copy
cdnjs
  3754 bytes (3.7k)
CDN, direct link
gzip -9
  3753 bytes (3.7k)
local copy
cdnhttps
  3731 bytes (3.6k)
CDN, direct link
unpkg
  3731 bytes (3.6k)
CDN, direct link
libdeflate -12
  3659 bytes (3.6k)
local copy
7zip -mx=9 -tgzip
  3653 bytes (3.6k)
local copy
pigz -11 -n
  3653 bytes (3.6k)
local copy
kzip -s0 -rn -b1
  3651 bytes (3.6k)
local copy
Zopfli
  3650 bytes (3.6k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/backbonejs/backbone-0.3.1.min.js

You will automatically get the smallest BackboneJS 0.3.1 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 81 bytes by using my BackboneJS 0.3.1 Zopfli version instead of the best available CDN (2.22% smaller than unpkg, 3650 vs. 3731 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 --mls512 --bsr6 --lazy --ohh

(found September 8, 2015)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 512  --mls512
block splitting recursion 6  --bsr6
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/0.3.1/backbone-min.js --location | md5sum
24006d96fb84506958f2e88e4d5933e4  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-0.3.1.min.zopfli.js.gz | md5sum
24006d96fb84506958f2e88e4d5933e4  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/backbone/0.3.1/backbone-min.js --location | sha1sum
7c01acd36fa76aeb2449a0bf0682eee40523be99  -
curl --silent --compressed http://minime.stephan-brumme.com/files/backbonejs/backbone-0.3.1.min.zopfli.js.gz | sha1sum
7c01acd36fa76aeb2449a0bf0682eee40523be99  -

CDN Size (compressed) MD5 (uncompressed) Comment / Diff Timestamp
Boot 4214 bytes 083308c10210d6677b1ef19756279206 < e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
< function(t){t.setRequestHeader("X-HTTP-Method-Override",i) [...]
> e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
> function(i){i.setRequestHeader("X-HTTP-Method-Override",g) [...]
(invalid)
cdnjs 3754 bytes 083308c10210d6677b1ef19756279206 < e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
< function(t){t.setRequestHeader("X-HTTP-Method-Override",i) [...]
> e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
> function(i){i.setRequestHeader("X-HTTP-Method-Override",g) [...]
(invalid)
cdnhttps 3731 bytes 083308c10210d6677b1ef19756279206 < e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
< function(t){t.setRequestHeader("X-HTTP-Method-Override",i) [...]
> e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
> function(i){i.setRequestHeader("X-HTTP-Method-Override",g) [...]
December 24, 2015 @ 07:32
unpkg 3731 bytes 083308c10210d6677b1ef19756279206 < e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
< function(t){t.setRequestHeader("X-HTTP-Method-Override",i) [...]
> e.View.extend=m;var s={create:"POST",update:"PUT","delete" [...]
> function(i){i.setRequestHeader("X-HTTP-Method-Override",g) [...]
July 11, 2016 @ 16:18

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
3650 bytes -1 byte zopfli --i10000 --mls512 --bsr6 --lazy --ohh September 8, 2015 @ 14:21
3651 bytes -2 bytes zopfli --i1000 --mls512 --bsr8 --lazy --ohh September 8, 2015 @ 11:50
3653 bytes zopfli --i100 --mls2048 --bsr13 --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
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650
3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650 3650

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 3651 bytes 100%
1,000 3651 bytes 100%
10,000 3650 bytes -1 byte 100%
100,000 3650 bytes 0.29%
1,000,000 3650 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
3652 bytes +2 bytes (+0.05%) +1 byte
3651 bytes +1 byte (+0.03%)
3678 bytes +28 bytes (+0.77%) +27 bytes
3716 bytes +66 bytes (+1.81%) +65 bytes
3729 bytes +79 bytes (+2.16%) +78 bytes
3768 bytes +118 bytes (+3.23%) +117 bytes
3809 bytes +159 bytes (+4.36%) +158 bytes
3841 bytes +191 bytes (+5.23%) +190 bytes
3872 bytes +222 bytes (+6.08%) +221 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 3273 bytes -377 bytes (-10.33%)
Brotli (Wikipedia) brotli brotli -q 11 3297 bytes -353 bytes (-9.67%)
ZSTD (Wikipedia) zstd zstd -19 3668 bytes +18 bytes (+0.49%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 3687 bytes +37 bytes (+1.01%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 3716 bytes +66 bytes (+1.81%)
LZMA2 (Wikipedia) xz xz -9 3728 bytes +78 bytes (+2.14%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 4113 bytes +463 bytes (+12.68%)

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