CLI Usage
Overview
-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.
`debug` Add debug prefix and suffix.
`domprops` Mangle property names that overlaps
with DOM properties.
`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.
-b, --beautify [options] Specify output 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.
-o, --output <file> Output file path (default STDOUT). Specify `ast` or
`spidermonkey` to write Terser 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
- 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, 6, 7 or 8.
-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 `output` options.
By default Terser 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 `output` options.
By default `terser` 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.
--verbose Print diagnostic messages.
--warn Print warning messages.
--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
Terser 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 Terser assumes HTTPX-SourceMapis being used and will omit the//# sourceMappingURL=directive.
For example:
terser 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). Terser has an option to take an input source map. Assuming you have a mapping from CoffeeScript → compiled JS, Terser 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:
terser 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 whereevalorwithare 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:
terser ... -m reserved=['$','require','exports']
to prevent the require, exports and $ names from being changed.
CLI mangling property names (--mangle-props)
Note: THIS WILL BREAK YOUR CODE. A good rule of thumb is not to use this unless you know exactly what you're doing and how this works and read this section until the end.
Mangling property names is a separate step, different from variable name mangling. Pass
--mangle-props to enable it. The least dangerous
way to use this is to use the regex option like so:
terser example.js -c -m --mangle-props regex=/_$/
This will mangle all properties that start with an underscore. So you can use it to mangle internal methods.
By default, it will mangle all properties in the input code with the exception of built in DOM properties and properties in core JavaScript classes, which is what will break your code if you don't:
- Control all the code you're mangling
- Avoid using a module bundler, as they usually will call Terser on each file individually, making it impossible to pass mangled objects between modules.
- Avoid calling functions like
definePropertyorhasOwnProperty, because they refer to object properties using strings and will break your code if you don't know what you are doing.
An example:
// example.js
var x = {
baz_: 0,
foo_: 1,
calc: function() {
return this.foo_ + this.baz_;
}
};
x.bar_ = 2;
x["baz_"] = 3;
console.log(x.calc());
Mangle all properties (except for JavaScript builtins) (very unsafe):
$ terser example.js -c -m --mangle-props
var x={o:0,_:1,l:function(){return this._+this.o}};x.t=2,x.o=3,console.log(x.l());
Mangle all properties except for reserved properties (still very unsafe):
$ terser example.js -c -m --mangle-props reserved=[foo_,bar_]
var x={o:0,foo_:1,_:function(){return this.foo_+this.o}};x.bar_=2,x.o=3,console.log(x._());
Mangle all properties matching a regex (not as unsafe but still unsafe):
$ terser example.js -c -m --mangle-props regex=/_$/
var x={o:0,_:1,calc:function(){return this._+this.o}};x.l=2,x.o=3,console.log(x.calc());
Combining mangle properties options:
$ terser example.js -c -m --mangle-props regex=/_$/,reserved=[bar_]
var x={o:0,_:1,calc:function(){return this._+this.o}};x.bar_=2,x.o=3,console.log(x.calc());
In order for this to be of any use, we avoid mangling standard JS names by
default (--mangle-props builtins to override).
A default exclusion file is provided in tools/domprops.json which should
cover most standard JS and DOM properties defined in various browsers. Pass
--mangle-props domprops to disable this feature.
A regular expression can be used to define which property names should be
mangled. For example, --mangle-props regex=/^_/ will only mangle property
names that start with an underscore.
When you compress multiple files using this option, in order for them to
work together in the end we need to ensure somehow that one property gets
mangled to the same name in all of them. For this, pass --name-cache filename.json
and Terser will maintain these mappings in a file which can then be reused.
It should be initially empty. Example:
$ rm -f /tmp/cache.json # start fresh
$ terser file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js
$ terser file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js
Now, part1.js and part2.js will be consistent with each other in terms
of mangled property names.
Using the name cache is not necessary if you compress all your files in a single call to Terser.
Mangling unquoted names (--mangle-props keep_quoted)
Using quoted property name (o["foo"]) reserves the property name (foo)
so that it is not mangled throughout the entire script even when used in an
unquoted style (o.foo). Example:
// stuff.js
var o = {
"foo": 1,
bar: 3
};
o.foo += o.bar;
console.log(o.foo);
$ terser stuff.js --mangle-props keep_quoted -c -m
var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo);
Debugging property name mangling
You can also pass --mangle-props debug in order to mangle property names
without completely obscuring them. For example the property o.foo
would mangle to o._$foo$_ with this option. This allows property mangling
of a large codebase while still being able to debug the code and identify
where mangling is breaking things.
$ terser stuff.js --mangle-props debug -c -m
var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_);
You can also pass a custom suffix using --mangle-props debug=XYZ. This would then
mangle o.foo to o._$foo$XYZ_. You can change this each time you compile a
script to identify how a property got mangled. One technique is to pass a
random number on every compile to simulate mangling changing with different
inputs (e.g. as you update the input script with new properties), and to help
identify mistakes like writing mangled keys to storage.