Choose a version:
29% The original file has 64060 bytes (62.6k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 18608 bytes (18.2k, 29%).

After GZIP compression these minified files vary in size:
unpkg
  7872 bytes (7.7k)
CDN
Boot
  7112 bytes (6.9k)
CDN
cdnjs
  7112 bytes (6.9k)
CDN
gzip -6 (default)
  7107 bytes (6.9k)
local copy
gzip -9
  7099 bytes (6.9k)
local copy
libdeflate -12
  6930 bytes (6.8k)
local copy
kzip -s0 -rn -b1
  6919 bytes (6.8k)
local copy
7zip -mx=9 -tgzip
  6918 bytes (6.8k)
local copy
zultra
  6918 bytes (6.8k)
local copy
pigz -11 -n
  6914 bytes (6.8k)
local copy
Zopfli
  6901 bytes (6.7k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.11.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.11.0 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 211 bytes by using my UnderscoreJS 1.11.0 Zopfli version instead of the best available CDN (3.06% smaller than cdnjs, 6901 vs. 7112 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 --mls2048 --bsr12 --lazy --ohh

(found September 2, 2020)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 2048  --mls2048
block splitting recursion 12  --bsr12
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/underscore/1.11.0/underscore-min.js --location | md5sum
22c3f342a6eabfd8eaf348eb24502037  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.11.0.min.zopfli.js.gz | md5sum
22c3f342a6eabfd8eaf348eb24502037  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.11.0/underscore-min.js --location | sha1sum
1981d5f5a37d4f0b46ced12159e3880b6623d9a7  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.11.0.min.zopfli.js.gz | sha1sum
1981d5f5a37d4f0b46ced12159e3880b6623d9a7  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 7872 bytes 22c3f342a6eabfd8eaf348eb24502037 (invalid)
Boot 7112 bytes 22c3f342a6eabfd8eaf348eb24502037 (invalid)
cdnjs 7112 bytes 22c3f342a6eabfd8eaf348eb24502037 (invalid)

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

Other Versions

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

1.11.0,
1.10.2, 1.10.1, 1.10.0,
1.9.2, 1.9.1, 1.9.0,
1.8.3, 1.8.2, 1.8.1,
1.7.0,
1.6.0,
1.5.2, 1.5.0,
1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0,
1.3.3, 1.3.2, 1.3.1, 1.3.0,
1.2.4, 1.2.3, 1.2.2, 1.2.1, 1.2.0,
1.1.7, 1.1.5, 1.1.4, 1.1.3, 1.1.2, 1.1.1, 1.1.0,
1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0.0,
0.6.0,
0.5.7, 0.5.6, 0.5.5, 0.5.4, 0.5.3, 0.5.2, 0.5.1, 0.5.0,
0.4.7, 0.4.6, 0.4.5, 0.4.4, 0.4.3, 0.4.2, 0.4.1, 0.4.0,
0.3.3, 0.3.2, 0.3.1, 0.3.0,
0.2.0,
0.1.1, 0.1.0

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

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
6901 bytes -1 byte zopfli --i1000000 --mls2048 --bsr12 --lazy --ohh September 2, 2020 @ 12:56
6902 bytes -1 byte zopfli --i10000 --mls16384 --bsr18 --lazy --ohh September 1, 2020 @ 16:30
6903 bytes -1 byte zopfli --i1000 --mls2048 --bsr9 --lazy --ohh September 1, 2020 @ 16:20
6904 bytes -3 bytes zopfli --i1000 --mls2048 --bsr12 --lazy --ohh September 1, 2020 @ 16:20
6907 bytes zopfli --i100 --mls4096 --bsr19 --lazy --ohh September 1, 2020 @ 15:43

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

Most recent activity on September 3, 2020 @ 02:41.

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
6910 6910 6910 6910 6910 6911 6910 6910 6911 6913 6907 6906 6906 6905 6906
6912 6912 6909 6912 6909 6908 6912 6911 6910 6913 6906 6902 6905 6904 6904
6918 6906 6909 6909 6909 6910 6909 6909 6912 6907 6908 6906 6907 6906 6906
6909 6909 6910 6909 6909 6909 6908 6908 6912 6904 6901 6906 6908 6909 6907
6909 6912 6910 6911 6910 6911 6909 6910 6911 6905 6907 6908 6907 6906 6906
6912 6909 6909 6912 6909 6911 6912 6911 6912 6904 6901 6906 6906 6902 6902
6917 6909 6909 6909 6909 6909 6909 6909 6909 6905 6905 6909 6908 6905 6906
6909 6909 6909 6910 6909 6909 6909 6910 6911 6904 6901 6908 6908 6905 6906
6909 6909 6910 6909 6909 6909 6909 6910 6906 6905 6901 6906 6906 6907 6906
6912 6909 6908 6909 6909 6909 6909 6909 6911 6905 6905 6902 6908 6906 6905
6909 6910 6909 6909 6909 6909 6909 6909 6910 6906 6905 6905 6908 6905 6905
6909 6909 6909 6909 6909 6909 6909 6909 6910 6904 6905 6908 6909 6906 6907
6909 6909 6908 6909 6909 6909 6909 6909 6912 6905 6906 6904 6908 6905 6906
6909 6911 6910 6909 6909 6909 6908 6909 6912 6905 6905 6908 6908 6905 6906
6909 6909 6909 6909 6911 6909 6909 6909 6911 6904 6907 6907 6904 6902 6901
6909 6909 6909 6909 6909 6909 6909 6909 6911 6905 6901 6901 6905 6907 6906
6918 6909 6909 6909 6909 6908 6909 6909 6909 6905 6901 6907 6908 6906 6906
6909 6908 6909 6909 6909 6909 6908 6909 6911 6904 6905 6908 6905 6913 6906
6909 6909 6908 6910 6911 6910 6909 6909 6911 6905 6905 6908 6908 6908 6906
6909 6908 6910 6909 6909 6909 6910 6909 6912 6904 6901 6908 6905 6906 6906
6909 6908 6910 6909 6909 6909 6909 6909 6911 6905 6909 6904 6905 6907 6906
6909 6910 6910 6909 6909 6907 6909 6909 6912 6905 6907 6907 6906 6905 6906
6910 6909 6909 6910 6909 6908 6909 6909 6912 6904 6905 6902 6905 6906 6906

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 6907 bytes 100%
1,000 6903 bytes -4 bytes 100%
10,000 6902 bytes -1 byte 100%
100,000 6902 bytes 4.35%
1,000,000 6901 bytes -1 byte 4.35%
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
6920 bytes +19 bytes (+0.28%) +1 byte
6919 bytes +18 bytes (+0.26%)
6924 bytes +23 bytes (+0.33%) +5 bytes
6944 bytes +43 bytes (+0.62%) +25 bytes
6977 bytes +76 bytes (+1.10%) +58 bytes
7009 bytes +108 bytes (+1.56%) +90 bytes
7047 bytes +146 bytes (+2.12%) +128 bytes
7069 bytes +168 bytes (+2.43%) +150 bytes
7099 bytes +198 bytes (+2.87%) +180 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - for example, your browser actually supports it !
Algorithm Program Parameters Size Compared To Best Zopfli
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 6212 bytes -689 bytes (-9.98%)
Brotli (Wikipedia) brotli brotli -q 11 6457 bytes -444 bytes (-6.43%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6580 bytes -321 bytes (-4.65%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 6896 bytes -5 bytes (-0.07%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 6903 bytes +2 bytes (+0.03%)
LZMA2 (Wikipedia) xz xz -9 6904 bytes +3 bytes (+0.04%)
Zstandard (Wikipedia) zstd zstd -19 6905 bytes +4 bytes (+0.06%)

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 2020.
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

All trademarks are property of their respective owners. You know, the boring legal stuff.