Choose a version:
29% The original file has 67455 bytes (65.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 19358 bytes (18.9k, 29%).

After GZIP compression these minified files vary in size:
unpkg
  8216 bytes (8.0k)
CDN
gzip -6 (default)
  7422 bytes (7.2k)
local copy
gzip -9
  7413 bytes (7.2k)
local copy
libdeflate -12
  7238 bytes (7.1k)
local copy
zultra
  7231 bytes (7.1k)
local copy
kzip -s0 -rn -b1
  7226 bytes (7.1k)
local copy
7zip -mx=9 -tgzip
  7225 bytes (7.1k)
local copy
pigz -11 -n
  7223 bytes (7.1k)
local copy
Zopfli
  7207 bytes (7.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.12.0 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 1009 bytes by using my UnderscoreJS 1.12.0 Zopfli version instead of the best available CDN (14.00% smaller than unpkg, 7207 vs. 8216 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 --mls16384 --bsr8 --lazy --ohh

(found December 1, 2020)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 16384  --mls16384
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/underscore/1.12.0/underscore-min.js --location | md5sum
5e69b8b4c93891157f2dac3721873c59  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.0.min.zopfli.js.gz | md5sum
5e69b8b4c93891157f2dac3721873c59  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.12.0/underscore-min.js --location | sha1sum
ac0bc40622bb3babcb228f3662b67ed8ae1012a3  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.0.min.zopfli.js.gz | sha1sum
ac0bc40622bb3babcb228f3662b67ed8ae1012a3  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 8216 bytes 5e69b8b4c93891157f2dac3721873c59 (invalid)

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

Other Versions

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

1.12.0,
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
7207 bytes -1 byte zopfli --i10000 --mls16384 --bsr8 --lazy --ohh December 1, 2020 @ 15:20
7208 bytes -1 byte zopfli --i10000 --mls256 --bsr20 --lazy --ohh December 1, 2020 @ 15:06
7209 bytes -3 bytes zopfli --i1000 --mls8192 --bsr2 --lazy --ohh December 1, 2020 @ 14:50
7212 bytes zopfli --i100 --mls8192 --bsr19 --lazy --ohh December 1, 2020 @ 14:30

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

Most recent activity on December 1, 2020 @ 19:02.

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
7219 7219 7219 7219 7219 7210 7221 7210 7220 7216 7211 7210 7208 7207 7209
7216 7221 7216 7218 7217 7216 7216 7215 7219 7221 7208 7208 7208 7209 7209
7217 7215 7216 7216 7218 7216 7216 7216 7221 7214 7208 7216 7208 7209 7208
7217 7216 7216 7217 7217 7216 7216 7218 7219 7216 7215 7210 7208 7208 7208
7217 7216 7219 7216 7217 7210 7216 7210 7221 7216 7209 7212 7208 7207 7209
7217 7216 7216 7219 7217 7215 7216 7215 7220 7214 7216 7216 7209 7208 7209
7217 7216 7216 7217 7218 7217 7216 7209 7220 7215 7209 7209 7208 7209 7209
7216 7216 7216 7217 7217 7210 7216 7210 7217 7216 7214 7208 7213 7211 7208
7217 7216 7216 7217 7218 7216 7217 7216 7209 7216 7209 7209 7208 7208 7208
7218 7216 7216 7216 7217 7216 7216 7216 7221 7216 7216 7212 7209 7208 7208
7218 7216 7217 7217 7217 7208 7216 7209 7220 7216 7213 7208 7208 7209 7209
7217 7216 7216 7217 7218 7216 7217 7218 7221 7210 7216 7208 7208 7209 7209
7217 7216 7216 7217 7215 7217 7217 7210 7221 7216 7209 7209 7209 7210 7209
7216 7216 7216 7217 7218 7215 7217 7208 7221 7216 7216 7209 7209 7211 7209
7217 7216 7216 7217 7217 7216 7217 7218 7217 7216 7209 7211 7208 7208 7208
7217 7216 7216 7217 7217 7216 7217 7218 7216 7216 7209 7209 7208 7209 7209
7217 7217 7217 7217 7217 7208 7216 7208 7221 7216 7216 7210 7208 7209 7209
7218 7216 7216 7216 7217 7215 7217 7217 7216 7216 7209 7209 7209 7208 7208
7217 7217 7216 7217 7217 7217 7216 7216 7221 7216 7209 7208 7209 7209 7208
7217 7216 7216 7217 7217 7216 7217 7208 7212 7214 7212 7209 7209 7208 7208
7219 7216 7216 7217 7217 7216 7216 7217 7221 7209 7208 7209 7209 7208 7208
7218 7216 7216 7216 7217 7216 7216 7210 7215 7215 7209 7210 7209 7210 7210
7220 7216 7219 7216 7218 7216 7216 7215 7209 7215 7209 7210 7209 7208 7208

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 7212 bytes 100%
1,000 7209 bytes -3 bytes 100%
10,000 7207 bytes -2 bytes 100%
100,000 7207 bytes 0.58%
1,000,000 7207 bytes 0.58%
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
7226 bytes +19 bytes (+0.26%)
7226 bytes +19 bytes (+0.26%)
7226 bytes +19 bytes (+0.26%)
7247 bytes +40 bytes (+0.56%) +21 bytes
7277 bytes +70 bytes (+0.97%) +51 bytes
7313 bytes +106 bytes (+1.47%) +87 bytes
7351 bytes +144 bytes (+2.00%) +125 bytes
7373 bytes +166 bytes (+2.30%) +147 bytes
7405 bytes +198 bytes (+2.75%) +179 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 6478 bytes -729 bytes (-10.12%)
Brotli (Wikipedia) brotli brotli -q 11 6751 bytes -456 bytes (-6.33%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6868 bytes -339 bytes (-4.70%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 7156 bytes -51 bytes (-0.71%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7199 bytes -8 bytes (-0.11%)
LZMA2 (Wikipedia) xz xz -9 7200 bytes -7 bytes (-0.10%)
Zstandard (Wikipedia) zstd zstd -19 7207 bytes (0.00%)

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 2021.
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.