Choose a version:
29% The original file has 68416 bytes (66.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 19526 bytes (19.1k, 29%).

After GZIP compression these minified files vary in size:
unpkg
  10252 bytes (10.0k)
 CDN
Boot
  7534 bytes (7.4k)
 CDN
cdnjs
  7526 bytes (7.3k)
 CDN
gzip -6 (default)
  7519 bytes (7.3k)
 local copy
gzip -9
  7510 bytes (7.3k)
 local copy
libdeflate -12
  7332 bytes (7.2k)
 local copy
zultra
  7321 bytes (7.1k)
 local copy
7zip -mx=9 -tgzip
  7320 bytes (7.1k)
 local copy
kzip -s0 -rn -b2
  7318 bytes (7.1k)
 local copy
pigz -11 -n
  7317 bytes (7.1k)
 local copy
Zopfli
  7302 bytes (7.1k)
 local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.6.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.13.6 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 224 bytes by using my UnderscoreJS 1.13.6 Zopfli version instead of the best available CDN (3.07% smaller than cdnjs, 7302 vs. 7526 bytes):
Download
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 --mls2048 --bsr40 --lazy --ohh

(found January 4, 2023)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 2048  --mls2048
block splitting recursion 40  --bsr40
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/1.13.6/underscore-min.js --location | md5sum
ee7696b2c3f3a27edf649af1fcfd73c9  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.6.min.zopfli.js.gz | md5sum
ee7696b2c3f3a27edf649af1fcfd73c9  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.13.6/underscore-min.js --location | sha1sum
86b8bf7695eb7935275fcc367dc49136914554ef  -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.6.min.zopfli.js.gz | sha1sum
86b8bf7695eb7935275fcc367dc49136914554ef  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 10252 bytes ee7696b2c3f3a27edf649af1fcfd73c9 (invalid)
Boot 7534 bytes ee7696b2c3f3a27edf649af1fcfd73c9 January 3, 2023 @ 16:20
cdnjs 7526 bytes ee7696b2c3f3a27edf649af1fcfd73c9 (invalid)

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

Other Versions

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

1.13.6, 1.13.5, 1.13.4, 1.13.3, 1.13.2, 1.13.1, 1.13.0,
1.12.1, 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
7302 bytes -1 byte zopfli --i100000 --mls2048 --bsr40 --lazy --ohh January 4, 2023 @ 11:11
7303 bytes -1 byte zopfli --i100000 --mls1024 --bsr12 --lazy --ohh January 4, 2023 @ 10:57
7304 bytes -1 byte zopfli --i1000 --mls2048 --bsr30 --lazy --ohh January 3, 2023 @ 18:18
7305 bytes -2 bytes zopfli --i1000 --mls1024 --bsr12 --lazy --ohh January 3, 2023 @ 18:16
7307 bytes – zopfli --i100 --mls2048 --bsr22 --lazy --ohh January 3, 2023 @ 16:37

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

Most recent activity on January 4, 2023 @ 19:49.

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
2 7313 7313 7314 7314 7314 7306 7307 7314 7306 7306 7306 7307 7304 7306 7306
4 7310 7310 7310 7311 7307 7310 7308 7312 7312 7312 7305 7303 7306 7306 7306
6 7312 7309 7310 7309 7307 7309 7309 7307 7310 7309 7305 7306 7306 7306 7306
7 7311 7312 7308 7310 7309 7309 7310 7311 7311 7303 7304 7306 7306 7306 7306
8 7310 7313 7310 7312 7309 7306 7305 7311 7305 7308 7306 7307 7306 7306 7306
9 7310 7314 7310 7310 7310 7310 7312 7311 7309 7308 7304 7306 7306 7306 7311
10 7311 7307 7310 7310 7307 7309 7312 7311 7310 7307 7303 7306 7307 7306 7306
11 7307 7308 7310 7311 7311 7307 7311 7311 7310 7308 7303 7307 7306 7311 7306
12 7311 7307 7310 7310 7308 7310 7311 7311 7306 7303 7305 7311 7306 7306 7306
13 7311 7313 7308 7309 7307 7309 7309 7311 7310 7308 7304 7308 7307 7306 7306
14 7309 7307 7309 7311 7307 7306 7304 7311 7310 7309 7305 7312 7307 7306 7306
15 7312 7309 7309 7310 7307 7309 7310 7311 7309 7305 7304 7307 7306 7306 7306
16 7312 7309 7310 7310 7309 7310 7311 7311 7308 7309 7303 7306 7306 7306 7306
17 7308 7309 7310 7310 7308 7310 7310 7309 7306 7309 7304 7306 7307 7306 7306
18 7311 7308 7309 7311 7308 7308 7310 7306 7309 7307 7303 7306 7306 7306 7306
19 7309 7309 7309 7310 7308 7310 7311 7311 7310 7310 7303 7304 7306 7306 7306
20 7309 7308 7310 7309 7308 7310 7309 7309 7306 7307 7306 7306 7306 7306 7306
21 7311 7308 7308 7311 7308 7312 7310 7311 7309 7308 7303 7304 7311 7306 7306
22 7309 7309 7308 7309 7307 7309 7309 7309 7309 7307 7302 7306 7306 7306 7306
23 7308 7308 7310 7309 7309 7310 7310 7311 7309 7308 7302 7304 7306 7306 7306
25 7310 7313 7310 7309 7308 7310 7310 7307 7312 7306 7303 7306 7306 7306 7306
30 7312 7312 7309 7310 7311 7311 7311 7311 7309 7307 7302 7305 7306 7306 7306
40 7310 7312 7309 7311 7311 7311 7311 7311 7310 7303 7302 7305 7306 7306 7306

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 7307 bytes – 100%
1,000 7304 bytes -3 bytes 100%
10,000 7304 bytes – 100%
100,000 7302 bytes -2 bytes 7.25%
1,000,000 7302 bytes – 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
(any) 7322 bytes +20 bytes (+0.27%) +4 bytes
1 7323 bytes +21 bytes (+0.29%) +5 bytes
2 7318 bytes +16 bytes (+0.22%) –
3 7342 bytes +40 bytes (+0.55%) +24 bytes
4 7370 bytes +68 bytes (+0.93%) +52 bytes
5 7398 bytes +96 bytes (+1.31%) +80 bytes
6 7433 bytes +131 bytes (+1.79%) +115 bytes
7 7457 bytes +155 bytes (+2.12%) +139 bytes
8 7478 bytes +176 bytes (+2.41%) +160 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 6564 bytes -738 bytes (-10.11%)
Brotli (Wikipedia) brotli brotli -q 11 6844 bytes -458 bytes (-6.27%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 6961 bytes -341 bytes (-4.67%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 7234 bytes -68 bytes (-0.93%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 7284 bytes -18 bytes (-0.25%)
LZMA2 (Wikipedia) xz xz -9 7284 bytes -18 bytes (-0.25%)
Zstandard (Wikipedia) zstd zstd -19 7298 bytes -4 bytes (-0.05%)

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):
Load and Parse Data


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 2026.
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.