Choose a version:
29% The original file has 60061 bytes (58.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 17532 bytes (17.1k, 29%).

After GZIP compression these minified files vary in size:
unpkg
  7475 bytes (7.3k)
CDN
gzip -6 (default)
  6730 bytes (6.6k)
local copy
gzip -9
  6728 bytes (6.6k)
local copy
7zip -mx=9 -tgzip
  6565 bytes (6.4k)
local copy
libdeflate -12
  6562 bytes (6.4k)
local copy
kzip -s0 -rn -b1
  6554 bytes (6.4k)
local copy
pigz -11 -n
  6554 bytes (6.4k)
local copy
zultra
  6553 bytes (6.4k)
local copy
Zopfli
  6533 bytes (6.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.10.0 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 942 bytes by using my UnderscoreJS 1.10.0 Zopfli version instead of the best available CDN (14.42% smaller than unpkg, 6533 vs. 7475 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 --mls16384 --bsr9 --lazy --ohh

(found April 15, 2020)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 16384  --mls16384
block splitting recursion 9  --bsr9
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/1.10.0/underscore-min.js --location | md5sum
c44dc23f3d73281b7019b116117530cc  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.0.min.zopfli.js.gz | md5sum
c44dc23f3d73281b7019b116117530cc  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.10.0/underscore-min.js --location | sha1sum
0a2b3a6d009f0744a8df514faaecca380c7581bd  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.0.min.zopfli.js.gz | sha1sum
0a2b3a6d009f0744a8df514faaecca380c7581bd  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 7475 bytes c44dc23f3d73281b7019b116117530cc (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
6533 bytes -1 byte zopfli --i100000 --mls16384 --bsr9 --lazy --ohh April 15, 2020 @ 18:04
6534 bytes -1 byte zopfli --i10000 --mls32768 --bsr9 --lazy --ohh April 15, 2020 @ 17:06
6535 bytes -1 byte zopfli --i1000 --mls16384 --bsr16 --lazy --ohh April 15, 2020 @ 15:43
6536 bytes -2 bytes zopfli --i1000 --mls8192 --bsr13 --lazy --ohh April 15, 2020 @ 15:42
6538 bytes zopfli --i100 --mls32768 --bsr7 --lazy --ohh April 14, 2020 @ 15:20

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

Most recent activity on July 20, 2020 @ 12:50.

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, 100,000 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
6554 6552 6554 6555 6554 6546 6546 6552 6549 6552 6553 6550 6553 6553 6553
6552 6552 6552 6553 6551 6543 6540 6543 6549 6548 6542 6538 6536 6535 6535
6544 6545 6549 6548 6549 6549 6548 6549 6549 6548 6543 6535 6535 6535 6535
6548 6537 6548 6546 6550 6537 6549 6548 6549 6548 6539 6538 6540 6534 6534
6552 6553 6548 6550 6553 6548 6554 6544 6544 6548 6545 6542 6536 6536 6536
6547 6553 6549 6547 6553 6541 6549 6549 6549 6549 6543 6537 6535 6533 6533
6548 6548 6551 6546 6549 6548 6550 6549 6542 6548 6543 6551 6554 6535 6535
6553 6553 6548 6548 6549 6545 6549 6549 6549 6548 6543 6553 6543 6535 6535
6555 6555 6555 6554 6537 6537 6540 6549 6549 6548 6548 6553 6553 6535 6534
6549 6549 6548 6548 6549 6549 6549 6547 6548 6549 6548 6535 6535 6535 6535
6554 6552 6543 6542 6542 6541 6542 6549 6547 6539 6544 6536 6535 6534 6534
6548 6548 6549 6549 6549 6539 6549 6548 6549 6549 6539 6542 6535 6535 6535
6548 6554 6548 6548 6535 6537 6537 6548 6550 6544 6539 6540 6535 6535 6535
6553 6553 6551 6548 6549 6535 6550 6551 6549 6549 6539 6542 6535 6535 6534
6548 6548 6548 6550 6552 6537 6537 6545 6549 6548 6545 6537 6551 6534 6534
6551 6553 6548 6547 6549 6537 6550 6549 6549 6548 6539 6552 6535 6535 6535
6547 6550 6549 6550 6552 6537 6539 6550 6551 6548 6539 6538 6535 6534 6534
6554 6553 6551 6548 6549 6549 6550 6549 6549 6546 6553 6541 6536 6536 6536
6549 6549 6548 6547 6553 6537 6537 6549 6549 6548 6543 6539 6536 6536 6536
6554 6553 6550 6548 6549 6549 6550 6549 6549 6548 6553 6540 6536 6536 6536
6554 6553 6548 6552 6549 6537 6549 6549 6549 6548 6546 6542 6552 6535 6535
6547 6553 6550 6548 6550 6548 6538 6549 6549 6550 6539 6540 6536 6536 6536
6548 6549 6549 6547 6549 6548 6550 6550 6550 6549 6538 6540 6535 6534 6535

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 6538 bytes 100%
1,000 6535 bytes -3 bytes 100%
10,000 6534 bytes -1 byte 100%
100,000 6533 bytes -1 byte 4.35%
1,000,000 6533 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
6554 bytes +21 bytes (+0.32%)
6554 bytes +21 bytes (+0.32%)
6569 bytes +36 bytes (+0.55%) +15 bytes
6593 bytes +60 bytes (+0.92%) +39 bytes
6610 bytes +77 bytes (+1.18%) +56 bytes
6614 bytes +81 bytes (+1.24%) +60 bytes
6643 bytes +110 bytes (+1.68%) +89 bytes
6679 bytes +146 bytes (+2.23%) +125 bytes
6708 bytes +175 bytes (+2.68%) +154 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 5859 bytes -674 bytes (-10.32%)
Brotli (Wikipedia) brotli brotli -q 11 6098 bytes -435 bytes (-6.66%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6113 bytes -420 bytes (-6.43%)
Zstandard (Wikipedia) zstd zstd -19 6524 bytes -9 bytes (-0.14%)
LZMA2 (Wikipedia) xz xz -9 6540 bytes +7 bytes (+0.11%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 6545 bytes +12 bytes (+0.18%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 6634 bytes +101 bytes (+1.55%)

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.