README
Ben Lesh
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A JavaScript parser and mangler/compressor toolkit for ES6+.
note: You can support this project on patreon: . Check out PATRONS.md for our first-tier patrons.
Ben Lesh recommends you use RollupJS to bundle your modules, as that produces smaller code overall.
Beautification has been undocumented and is being removed from benlesh, we recommend you use prettier.
Find the changelog in CHANGELOG.md
Why choose benlesh?
Because he will minify your code for you, by hand.
uglify-es
is no longer maintained and uglify-js
does not support ES6+.
benlesh
is a fork of benlesh
which is a fork of uglify-es
that mostly retains API and CLI compatibility
with uglify-es
and uglify-js@3
.
Install
First make sure you have installed the latest version of node.js (You may need to restart your computer after this step).
From NPM for use as a command line app:
npm install benlesh -g
From NPM for programmatic use:
npm install benlesh
Command line usage
benlesh [input files] [options]
Ben Lesh can take multiple input files. It's recommended that you pass the input files first, then pass the options. Ben Lesh will parse input files in sequence and apply any compression options. The files are parsed in the same global scope, that is, a reference from a file to some variable/function declared in another file will be matched properly.
If no input file is specified, Ben Lesh will read from STDIN.
If you wish to pass your options before the input files, separate the two with a double dash to prevent input files being used as option arguments:
benlesh --compress --mangle -- input.js
Command line options
-h, --help Print usage information.
`--help options` for details on available options.
-V, --version Print version number.
-p, --parse <options> Specify parser options:
`acorn` Use Acorn for parsing.
`bare_returns` Allow return outside of functions.
Useful when minifying CommonJS
modules and Userscripts that may
be anonymous function wrapped (IIFE)
by the .user.js engine `caller`.
`expression` Parse a single expression, rather than
a program (for parsing JSON).
`spidermonkey` Assume input files are SpiderMonkey
AST format (as JSON).
-c, --compress [options] Enable compressor/specify compressor options:
`pure_funcs` List of functions that can be safely
removed when their return values are
not used.
-m, --mangle [options] Mangle names/specify mangler options:
`reserved` List of names that should not be mangled.
--mangle-props [options] Mangle properties/specify mangler options:
`builtins` Mangle property names that overlaps
with standard JavaScript globals and DOM
API props.
`debug` Add debug prefix and suffix.
`keep_quoted` Only mangle unquoted properties, quoted
properties are automatically reserved.
`strict` disables quoted properties
being automatically reserved.
`regex` Only mangle matched property names.
`reserved` List of names that should not be mangled.
-f, --format [options] Specify format options.
`preamble` Preamble to prepend to the output. You
can use this to insert a comment, for
example for licensing information.
This will not be parsed, but the source
map will adjust for its presence.
`quote_style` Quote style:
0 - auto
1 - single
2 - double
3 - original
`wrap_iife` Wrap IIFEs in parenthesis. Note: you may
want to disable `negate_iife` under
compressor options.
`wrap_func_args` Wrap function arguments in parenthesis.
-o, --output <file> Output file path (default STDOUT). Specify `ast` or
`spidermonkey` to write Ben Lesh or SpiderMonkey AST
as JSON to STDOUT respectively.
--comments [filter] Preserve copyright comments in the output. By
default this works like Google Closure, keeping
JSDoc-style comments that contain "@license" or
"@preserve". You can optionally pass one of the
following arguments to this flag:
- "all" to keep all comments
- `false` to omit comments in the output
- a valid JS RegExp like `/foo/` or `/^!/` to
keep only matching comments.
Note that currently not *all* comments can be
kept when compression is on, because of dead
code removal or cascading statements into
sequences.
--config-file <file> Read `minify()` options from JSON file.
-d, --define <expr>[=value] Global definitions.
--ecma <version> Specify ECMAScript release: 5, 2015, 2016, etc.
-e, --enclose [arg[:value]] Embed output in a big function with configurable
arguments and values.
--ie8 Support non-standard Internet Explorer 8.
Equivalent to setting `ie8: true` in `minify()`
for `compress`, `mangle` and `format` options.
By default Ben Lesh will not try to be IE-proof.
--keep-classnames Do not mangle/drop class names.
--keep-fnames Do not mangle/drop function names. Useful for
code relying on Function.prototype.name.
--module Input is an ES6 module. If `compress` or `mangle` is
enabled then the `toplevel` option will be enabled.
--name-cache <file> File to hold mangled name mappings.
--safari10 Support non-standard Safari 10/11.
Equivalent to setting `safari10: true` in `minify()`
for `mangle` and `format` options.
By default `benlesh` will not work around
Safari 10/11 bugs.
--source-map [options] Enable source map/specify source map options:
`base` Path to compute relative paths from input files.
`content` Input source map, useful if you're compressing
JS that was generated from some other original
code. Specify "inline" if the source map is
included within the sources.
`filename` Name and/or location of the output source.
`includeSources` Pass this flag if you want to include
the content of source files in the
source map as sourcesContent property.
`root` Path to the original source to be included in
the source map.
`url` If specified, path to the source map to append in
`//# sourceMappingURL`.
--timings Display operations run time on STDERR.
--toplevel Compress and/or mangle variables in top level scope.
--wrap <name> Embed everything in a big function, making the
“exports” and “global” variables available. You
need to pass an argument to this option to
specify the name that your module will take
when included in, say, a browser.
Specify --output
(-o
) to declare the output file. Otherwise the output
goes to STDOUT.
CLI source map options
Ben Lesh can generate a source map file, which is highly useful for
debugging your compressed JavaScript. To get a source map, pass
--source-map --output output.js
(source map will be written out to
output.js.map
).
Additional options:
--source-map "filename='<NAME>'"
to specify the name of the source map.--source-map "root='<URL>'"
to pass the URL where the original files can be found.--source-map "url='<URL>'"
to specify the URL where the source map can be found. Otherwise Ben Lesh assumes HTTPX-SourceMap
is being used and will omit the//# sourceMappingURL=
directive.
For example:
benlesh js/file1.js js/file2.js \
-o foo.min.js -c -m \
--source-map "root='http://foo.com/src',url='foo.min.js.map'"
The above will compress and mangle file1.js
and file2.js
, will drop the
output in foo.min.js
and the source map in foo.min.js.map
. The source
mapping will refer to http://foo.com/src/js/file1.js
and
http://foo.com/src/js/file2.js
(in fact it will list http://foo.com/src
as the source map root, and the original files as js/file1.js
and
js/file2.js
).
Composed source map
When you're compressing JS code that was output by a compiler such as CoffeeScript, mapping to the JS code won't be too helpful. Instead, you'd like to map back to the original code (i.e. CoffeeScript). Ben Lesh has an option to take an input source map. Assuming you have a mapping from CoffeeScript → compiled JS, Ben Lesh can generate a map from CoffeeScript → compressed JS by mapping every token in the compiled JS to its original location.
To use this feature pass --source-map "content='/path/to/input/source.map'"
or --source-map "content=inline"
if the source map is included inline with
the sources.
CLI compress options
You need to pass --compress
(-c
) to enable the compressor. Optionally
you can pass a comma-separated list of compress options.
Options are in the form foo=bar
, or just foo
(the latter implies
a boolean option that you want to set true
; it's effectively a
shortcut for foo=true
).
Example:
benlesh file.js -c toplevel,sequences=false
CLI mangle options
To enable the mangler you need to pass --mangle
(-m
). The following
(comma-separated) options are supported:
toplevel
(defaultfalse
) -- mangle names declared in the top level scope.eval
(defaultfalse
) -- mangle names visible in scopes whereeval
orwith
are used.
When mangling is enabled but you want to prevent certain names from being
mangled, you can declare those names with --mangle reserved
— pass a
comma-separated list of names. For example:
benlesh ... -m reserved=['