Choose a version:
29% The original file has 60068 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 17547 bytes (17.1k, 29%).

After GZIP compression these minified files vary in size:
unpkg
  7483 bytes (7.3k)
CDN
Boot
  6745 bytes (6.6k)
CDN
cdnjs
  6745 bytes (6.6k)
CDN
gzip -6 (default)
  6741 bytes (6.6k)
local copy
gzip -9
  6737 bytes (6.6k)
local copy
libdeflate -12
  6572 bytes (6.4k)
local copy
7zip -mx=9 -tgzip
  6570 bytes (6.4k)
local copy
kzip -s0 -rn -b0
  6563 bytes (6.4k)
local copy
pigz -11 -n
  6559 bytes (6.4k)
local copy
Zopfli
  6543 bytes (6.4k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.10.2 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 202 bytes by using my UnderscoreJS 1.10.2 Zopfli version instead of the best available CDN (3.09% smaller than cdnjs, 6543 vs. 6745 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 --mls8192 --bsr9 --lazy --ohh

(found May 19, 2020)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 8192  --mls8192
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/1.10.2/underscore-min.js --location | md5sum
52caef864228e0b4ca9f97eced0ab2bb  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.2.min.zopfli.js.gz | md5sum
52caef864228e0b4ca9f97eced0ab2bb  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.10.2/underscore-min.js --location | sha1sum
e4cf51325358922e7ceb95707827ba7f19d7fc18  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.2.min.zopfli.js.gz | sha1sum
e4cf51325358922e7ceb95707827ba7f19d7fc18  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 7483 bytes 52caef864228e0b4ca9f97eced0ab2bb (invalid)
Boot 6745 bytes 52caef864228e0b4ca9f97eced0ab2bb May 30, 2020 @ 05:16
cdnjs 6745 bytes 52caef864228e0b4ca9f97eced0ab2bb May 30, 2020 @ 05:16

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

Other Versions

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

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
6543 bytes -1 byte zopfli --i1000000 --mls8192 --bsr9 --lazy --ohh May 19, 2020 @ 19:01
6544 bytes -2 bytes zopfli --i10000 --mls2048 --bsr14 --lazy --ohh May 19, 2020 @ 14:38
6546 bytes -2 bytes zopfli --i1000 --mls2048 --bsr14 --lazy --ohh May 19, 2020 @ 14:36
6548 bytes zopfli --i100 --mls2048 --bsr14 --lazy --ohh May 19, 2020 @ 14:32

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

Most recent activity on May 30, 2020 @ 05:16.

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
6564 6564 6563 6565 6564 6554 6560 6559 6559 6562 6562 6562 6562 6562 6562
6561 6559 6560 6560 6558 6552 6551 6553 6553 6556 6556 6562 6548 6547 6547
6559 6564 6559 6559 6559 6559 6557 6554 6558 6556 6545 6545 6561 6552 6552
6559 6559 6560 6554 6558 6554 6564 6559 6560 6560 6557 6562 6546 6546 6546
6564 6564 6558 6559 6564 6565 6563 6558 6555 6558 6562 6552 6545 6546 6546
6557 6557 6556 6549 6562 6553 6551 6554 6558 6560 6546 6562 6543 6548 6548
6559 6560 6558 6559 6559 6559 6560 6559 6553 6549 6562 6562 6563 6546 6546
6563 6563 6559 6559 6559 6559 6564 6560 6559 6558 6552 6562 6546 6546 6546
6565 6564 6565 6563 6565 6554 6548 6557 6559 6558 6545 6562 6563 6547 6546
6556 6558 6558 6559 6558 6559 6563 6559 6558 6558 6545 6546 6546 6548 6548
6564 6564 6559 6552 6552 6556 6552 6554 6558 6551 6543 6546 6545 6547 6547
6559 6559 6556 6559 6556 6559 6565 6559 6558 6558 6556 6562 6550 6548 6548
6559 6558 6558 6552 6558 6556 6548 6559 6558 6558 6549 6548 6545 6548 6548
6564 6564 6558 6559 6559 6559 6548 6561 6559 6559 6546 6548 6545 6548 6547
6564 6565 6558 6559 6558 6556 6548 6554 6558 6550 6546 6546 6564 6546 6546
6555 6556 6558 6555 6559 6556 6556 6559 6559 6558 6545 6546 6545 6547 6547
6559 6564 6558 6558 6555 6557 6549 6558 6558 6558 6549 6546 6545 6552 6552
6564 6563 6559 6564 6559 6559 6560 6559 6558 6559 6562 6549 6546 6549 6549
6559 6564 6558 6558 6559 6556 6563 6559 6559 6556 6545 6546 6546 6547 6547
6563 6563 6558 6558 6558 6559 6558 6559 6558 6558 6545 6560 6546 6547 6547
6564 6564 6558 6559 6558 6559 6549 6558 6558 6558 6553 6562 6563 6550 6550
6559 6559 6559 6559 6559 6559 6552 6558 6558 6556 6545 6548 6562 6546 6546
6559 6564 6560 6559 6558 6559 6560 6560 6559 6558 6543 6544 6545 6545 6546

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 6548 bytes 100%
1,000 6546 bytes -2 bytes 100%
10,000 6544 bytes -2 bytes 100%
100,000 6544 bytes 2.03%
1,000,000 6543 bytes -1 byte 1.16%
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
6563 bytes +20 bytes (+0.31%)
6563 bytes +20 bytes (+0.31%)
6579 bytes +36 bytes (+0.55%) +16 bytes
6603 bytes +60 bytes (+0.92%) +40 bytes
6620 bytes +77 bytes (+1.18%) +57 bytes
6624 bytes +81 bytes (+1.24%) +61 bytes
6653 bytes +110 bytes (+1.68%) +90 bytes
6690 bytes +147 bytes (+2.25%) +127 bytes
6714 bytes +171 bytes (+2.61%) +151 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 5867 bytes -676 bytes (-10.33%)
Brotli (Wikipedia) brotli brotli -q 11 6110 bytes -433 bytes (-6.62%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6120 bytes -423 bytes (-6.46%)
Zstandard (Wikipedia) zstd zstd -19 6534 bytes -9 bytes (-0.14%)
LZMA2 (Wikipedia) xz xz -9 6548 bytes +5 bytes (+0.08%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 6557 bytes +14 bytes (+0.21%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 6644 bytes +101 bytes (+1.54%)

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.