README
UglifyJS 2
UglifyJS is a JavaScript parser, minifier, compressor or beautifier toolkit.
This page documents the command line utility. For API and internals documentation see my website. There's also an in-browser online demo (for Firefox, Chrome and probably Safari).
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 uglify-js -g
From NPM for programmatic use:
npm install uglify-js
From Git:
git clone git://github.com/mishoo/UglifyJS2.git
cd UglifyJS2
npm link .
Usage
uglifyjs [input files] [options]
UglifyJS2 can take multiple input files. It's recommended that you pass the input files first, then pass the options. UglifyJS 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 you want to read from STDIN instead, pass a single dash instead of input files.
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:
uglifyjs --compress --mangle -- input.js
The available options are:
--source-map Specify an output file where to generate source
map.
--source-map-root The path to the original source to be included
in the source map.
--source-map-url The path to the source map to be added in //#
sourceMappingURL. Defaults to the value passed
with --source-map.
--source-map-include-sources Pass this flag if you want to include the
content of source files in the source map as
sourcesContent property.
--in-source-map Input source map, useful if you're compressing
JS that was generated from some other original
code.
--screw-ie8 Use this flag if you don't wish to support
Internet Explorer 6-8 quirks.
By default UglifyJS will not try to be IE-proof.
--support-ie8 Use this flag to support Internet Explorer 6-8 quirks.
Note: may break standards compliant `catch` identifiers.
--expr Parse a single expression, rather than a
program (for parsing JSON)
-p, --prefix Skip prefix for original filenames that appear
in source maps. For example -p 3 will drop 3
directories from file names and ensure they are
relative paths. You can also specify -p
relative, which will make UglifyJS figure out
itself the relative paths between original
sources, the source map and the output file.
-o, --output Output file (default STDOUT).
-b, --beautify Beautify output/specify output options.
-m, --mangle Mangle names/pass mangler options.
-r, --reserved Reserved names to exclude from mangling.
-c, --compress Enable compressor/pass compressor options. Pass
options like -c
hoist_vars=false,if_return=false. Use -c with
no argument to use the default compression
options.
-d, --define Global definitions
-e, --enclose Embed everything in a big function, with a
configurable parameter/argument list.
--comments 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 (needs to start with a
slash) to keep only comments that match.
Note that currently not *all* comments can be
kept when compression is on, because of dead
code removal or cascading statements into
sequences.
--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.
--stats Display operations run time on STDERR.
--acorn Use Acorn for parsing.
--spidermonkey Assume input files are SpiderMonkey AST format
(as JSON).
--self Build itself (UglifyJS2) as a library (implies
--wrap=UglifyJS --export-all)
--wrap 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.
--export-all Only used when --wrap, this tells UglifyJS to
add code to automatically export all globals.
--lint Display some scope warnings
-v, --verbose Verbose
-V, --version Print version number and exit.
--noerr Don't throw an error for unknown options in -c,
-b or -m.
--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`.
--keep-fnames Do not mangle/drop function names. Useful for
code relying on Function.prototype.name.
--reserved-file File containing reserved names
--reserve-domprops Make (most?) DOM properties reserved for
--mangle-props
--mangle-props Mangle property names (default `0`). Set to
`true` or `1` to mangle all property names. Set
to `unquoted` or `2` to only mangle unquoted
property names. Mode `2` also enables the
`keep_quoted_props` beautifier option to
preserve the quotes around property names and
disables the `properties` compressor option to
prevent rewriting quoted properties with dot
notation. You can override these by setting
them explicitly on the command line.
--mangle-regex Only mangle property names matching the regex
--name-cache File to hold mangled names mappings
--pure-funcs List of functions that can be safely removed if
their return value is not used [array]
Specify --output
(-o
) to declare the output file. Otherwise the output
goes to STDOUT.
Source map options
UglifyJS2 can generate a source map file, which is highly useful for
debugging your compressed JavaScript. To get a source map, pass
--source-map output.js.map
(full path to the file where you want the
source map dumped).
Additionally you might need --source-map-root
to pass the URL where the
original files can be found. In case you are passing full paths to input
files to UglifyJS, you can use --prefix
(-p
) to specify the number of
directories to drop from the path prefix when declaring files in the source
map.
For example:
uglifyjs /home/doe/work/foo/src/js/file1.js \
/home/doe/work/foo/src/js/file2.js \
-o foo.min.js \
--source-map foo.min.js.map \
--source-map-root http://foo.com/src \
-p 5 -c -m
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). UglifyJS has an option to take an input source map. Assuming you have a mapping from CoffeeScript → compiled JS, UglifyJS can generate a map from CoffeeScript → compressed JS by mapping every token in the compiled JS to its original location.
To use this feature you need to pass --in-source-map /path/to/input/source.map
. Normally the input source map should also point
to the file containing the generated JS, so if that's correct you can omit
input files from the command line.
Mangler options
To enable the mangler you need to pass --mangle
(-m
). The following
(comma-separated) options are supported:
toplevel
— mangle names declared in the toplevel scope (disabled by default).eval
— mangle names visible in scopes whereeval
orwith
are used (disabled by default).
When mangling is enabled but you want to prevent certain names from being
mangled, you can declare those names with --reserved
(-r
) — pass a
comma-separated list of names. For example:
uglifyjs ... -m -r '$,require,exports'
to prevent the require
, exports
and $
names from being changed.
--mangle-props
)
Mangling property names (Note: this will probably break your code. Mangling property names is a
separate step, different from variable name mangling. Pass
--mangle-props
. It will mangle all properties that are seen in some
object literal, or that are assigned to. For example:
var x = {
foo: 1
};
x.bar = 2;
x["baz"] = 3;
x[condition ? "moo" : "boo"] = 4;
console.log(x.something());
In the above code, foo
, bar
, baz
, moo
and boo
will be replaced
with single characters, while something()
will be left as is.
In order for this to be of any use, we should avoid mangling standard JS
names. For instance, if your code would contain x.length = 10
, then
length
becomes a candidate for mangling and it will be mangled throughout
the code, regardless if it's being used as part of your own objects or
accessing an array's length. To avoid that, you can use --reserved-file
to pass a filename that should contain the names to be excluded from
mangling. This file can be used both for excluding variable names and
property names. It could look like this, for example:
{
"vars": [ "define", "require", ... ],
"props": [ "length", "prototype", ... ]
}
--reserved-file
can be an array of file names (either a single
comma-separated argument, or you can pass multiple --reserved-file
arguments) — in this case it will exclude names from all those files.
A default exclusion file is provided in tools/domprops.json
which should
cover most standard JS and DOM properties defined in various browsers. Pass
--reserve-domprops
to read that in.
You can also use a regular expression to define which property names should be
mangled. For example, --mangle-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 UglifyJS 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
uglifyjs file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js
uglifyjs 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 UglifyJS.
Compressor options
You need to pass --compress
(-c
) to enable the compressor. Optionally
you can pass a comma-separated list of 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
).
sequences
(default: true) -- join consecutive simple statements using the comma operator. May be set to a positive integer to specify the maximum number of consecutive comma sequences that will be generated. If this option is set totrue
then the defaultsequences
limit is200
. Set option tofalse
or0
to disable. The smallestsequences
length is2
. Asequences
value of1
is grandfathered to be equivalent totrue
and as such means200
. On rare occasions the default sequences limit leads to very slow compress times in which case a value of20
or less is recommended.properties
-- rewrite property access using the dot notation, for examplefoo["bar"] → foo.bar
dead_code
-- remove unreachable codedrop_debugger
-- removedebugger;
statementsunsafe
(default: false) -- apply "unsafe" transformations (discussion below)unsafe_comps
(default: false) -- Reverse<
and<=
to>
and>=
to allow improved compression. This might be unsafe when an at least one of two operands is an object with computed values due the use of methods likeget
, orvalueOf
. This could cause change in execution order after operands in the comparison are switching. Compression only works if bothcomparisons
andunsafe_comps
are both set to true.conditionals
-- apply optimizations forif
-s and conditional expressionscomparisons
-- apply certain optimizations to binary nodes, for example:!(a <= b) → a > b
(only whenunsafe_comps
), attempts to negate binary nodes, e.g.a = !b && !c && !d && !e → a=!(b||c||d||e)
etc.evaluate
-- attempt to evaluate constant expressionsbooleans
-- various optimizations for boolean context, for example!!a ? b : c → a ? b : c
loops
-- optimizations fordo
,while
andfor
loops when we can statically determine the conditionunused
-- drop unreferenced functions and variableshoist_funs
-- hoist function declarationshoist_vars
(default: false) -- hoistvar
declarations (this isfalse
by default because it seems to increase the size of the output in general)if_return
-- optimizations for if/return and if/continuejoin_vars
-- join consecutivevar
statementscascade
-- small optimization for sequences, transformx, x
intox
andx = something(), x
intox = something()
collapse_vars
-- defaultfalse
. Collapse single-usevar
andconst
definitions when possible.warnings
-- display warnings when dropping unreachable code or unused declarations etc.negate_iife
-- negate "Immediately-Called Function Expressions" where the return value is discarded, to avoid the parens that the code generator would insert.pure_getters
-- the default isfalse
. If you passtrue
for this, UglifyJS will assume that object property access (e.g.foo.bar
orfoo["bar"]
) doesn't have any side effects.pure_funcs
-- defaultnull
. You can pass an array of names and UglifyJS will assume that those functions do not produce side effects. DANGER: will not check if the name is redefined in scope. An example case here, for instancevar q = Math.floor(a/b)
. If variableq
is not used elsewhere, UglifyJS will drop it, but will still keep theMath.floor(a/b)
, not knowing what it does. You can passpure_funcs: [ 'Math.floor' ]
to let it know that this function won't produce any side effect, in which case the whole statement would get discarded. The current implementation adds some overhead (compression will be slower).drop_console
-- defaultfalse
. Passtrue
to discard calls toconsole.*
functions.keep_fargs
-- defaulttrue
. Prevents the compressor from discarding unused function arguments. You need this for code which relies onFunction.length
.keep_fnames
-- defaultfalse
. Passtrue
to prevent the compressor from discarding function names. Useful for code relying onFunction.prototype.name
. See also: thekeep_fnames
mangle option.passes
-- default1
. Number of times to run compress. Use an integer argument larger than 1 to further reduce code size in some cases. Note: raising the number of passes will increase uglify compress time.
unsafe
option
The It enables some transformations that might break code logic in certain contrived cases, but should be fine for most code. You might want to try it on your own code, it should reduce the minified size. Here's what happens when this flag is on:
new Array(1, 2, 3)
orArray(1, 2, 3)
→[ 1, 2, 3 ]
new Object()
→{}
String(exp)
orexp.toString()
→"" + exp
new Object/RegExp/Function/Error/Array (...)
→ we discard thenew
typeof foo == "undefined"
→foo === void 0
void 0
→undefined
(if there is a variable named "undefined" in scope; we do it because the variable name will be mangled, typically reduced to a single character)
Conditional compilation
You can use the --define
(-d
) switch in order to declare global
variables that UglifyJS will assume to be constants (unless defined in
scope). For example if you pass --define DEBUG=false
then, coupled with
dead code removal UglifyJS will discard the following from the output:
if (DEBUG) {
console.log("debug stuff");
}
UglifyJS will warn about the condition being always false and about dropping
unreachable code; for now there is no option to turn off only this specific
warning, you can pass warnings=false
to turn off all warnings.
Another way of doing that is to declare your globals as constants in a
separate file and include it into the build. For example you can have a
build/defines.js
file with the following:
const DEBUG = false;
const PRODUCTION = true;
// Alternative for environments that don't support `const`
/** @const */ var STAGING = false;
// etc.
and build your code like this:
uglifyjs build/defines.js js/foo.js js/bar.js... -c
UglifyJS will notice the constants and, since they cannot be altered, it
will evaluate references to them to the value itself and drop unreachable
code as usual. The build will contain the const
declarations if you use
them. If you are targeting < ES6 environments, use /** @const */ var
.
Conditional compilation, API
You can also use conditional compilation via the programmatic API. With the difference that the
property name is global_defs
and is a compressor property:
uglifyJS.minify([ "input.js"], {
compress: {
dead_code: true,
global_defs: {
DEBUG: false
}
}
});
Beautifier options
The code generator tries to output shortest code possible by default. In
case you want beautified output, pass --beautify
(-b
). Optionally you
can pass additional arguments that control the code output:
beautify
(defaulttrue
) -- whether to actually beautify the output. Passing-b
will set this to true, but you might need to pass-b
even when you want to generate minified code, in order to specify additional arguments, so you can use-b beautify=false
to override it.indent-level
(default 4)indent-start
(default 0) -- prefix all lines by that many spacesquote-keys
(defaultfalse
) -- passtrue
to quote all keys in literal objectsspace-colon
(defaulttrue
) -- insert a space after the colon signsascii-only
(defaultfalse
) -- escape Unicode characters in strings and regexps (affects directives with non-ascii characters becoming invalid)inline-script
(defaultfalse
) -- escape the slash in occurrences of</script
in stringswidth
(default 80) -- only takes effect when beautification is on, this specifies an (orientative) line width that the beautifier will try to obey. It refers to the width of the line text (excluding indentation). It doesn't work very well currently, but it does make the code generated by UglifyJS more readable.max-line-len
(default 32000) -- maximum line length (for uglified code)bracketize
(defaultfalse
) -- always insert brackets inif
,for
,do
,while
orwith
statements, even if their body is a single statement.semicolons
(defaulttrue
) -- separate statements with semicolons. If you passfalse
then whenever possible we will use a newline instead of a semicolon, leading to more readable output of uglified code (size before gzip could be smaller; size after gzip insignificantly larger).preamble
(defaultnull
) -- when passed it must be a string and it will be prepended to the output literally. The source map will adjust for this text. Can be used to insert a comment containing licensing information, for example.quote_style
(default0
) -- preferred quote style for strings (affects quoted property names and directives as well):0
-- prefers double quotes, switches to single quotes when there are more double quotes in the string itself.1
-- always use single quotes2
-- always use double quotes3
-- always use the original quotes
keep_quoted_props
(defaultfalse
) -- when turned on, prevents stripping quotes from property names in object literals.
Keeping copyright notices or other comments
You can pass --comments
to retain certain comments in the output. By
default it will keep JSDoc-style comments that contain "@preserve",
"@license" or "@cc_on" (conditional compilation for IE). You can pass
--comments all
to keep all the comments, or a valid JavaScript regexp to
keep only comments that match this regexp. For example --comments '/foo|bar/'
will keep only comments that contain "foo" or "bar".
Note, however, that there might be situations where comments are lost. For example:
function f() {
/** @preserve Foo Bar */
function g() {
// this function is never called
}
return something();
}
Even though it has "@preserve", the comment will be lost because the inner
function g
(which is the AST node to which the comment is attached to) is
discarded by the compressor as not referenced.
The safest comments where to place copyright information (or other info that needs to be kept in the output) are comments attached to toplevel nodes.
Support for the SpiderMonkey AST
UglifyJS2 has its own abstract syntax tree format; for practical reasons we can't easily change to using the SpiderMonkey AST internally. However, UglifyJS now has a converter which can import a SpiderMonkey AST.
For example Acorn is a super-fast parser that produces a SpiderMonkey AST. It has a small CLI utility that parses one file and dumps the AST in JSON on the standard output. To use UglifyJS to mangle and compress that:
acorn file.js | uglifyjs --spidermonkey -m -c
The --spidermonkey
option tells UglifyJS that all input files are not
JavaScript, but JS code described in SpiderMonkey AST in JSON. Therefore we
don't use our own parser in this case, but just transform that AST into our
internal AST.
Use Acorn for parsing
More for fun, I added the --acorn
option which will use Acorn to do all
the parsing. If you pass this option, UglifyJS will require("acorn")
.
Acorn is really fast (e.g. 250ms instead of 380ms on some 650K code), but converting the SpiderMonkey tree that Acorn produces takes another 150ms so in total it's a bit more than just using UglifyJS's own parser.
Using UglifyJS to transform SpiderMonkey AST
Now you can use UglifyJS as any other intermediate tool for transforming JavaScript ASTs in SpiderMonkey format.
Example:
function uglify(ast, options, mangle) {
// Conversion from SpiderMonkey AST to internal format
var uAST = UglifyJS.AST_Node.from_mozilla_ast(ast);
// Compression
uAST.figure_out_scope();
uAST = uAST.transform(UglifyJS.Compressor(options));
// Mangling (optional)
if (mangle) {
uAST.figure_out_scope();
uAST.compute_char_frequency();
uAST.mangle_names();
}
// Back-conversion to SpiderMonkey AST
return uAST.to_mozilla_ast();
}
Check out original blog post for details.
API Reference
Assuming installation via NPM, you can load UglifyJS in your application like this:
var UglifyJS = require("uglify-js");
It exports a lot of names, but I'll discuss here the basics that are needed for parsing, mangling and compressing a piece of code. The sequence is (1) parse, (2) compress, (3) mangle, (4) generate output code.
The simple way
There's a single toplevel function which combines all the steps. If you
don't need additional customization, you might want to go with minify
.
Example:
var result = UglifyJS.minify("/path/to/file.js");
console.log(result.code); // minified output
// if you need to pass code instead of file name
var result = UglifyJS.minify("var b = function () {};", {fromString: true});
You can also compress multiple files:
var result = UglifyJS.minify([ "file1.js", "file2.js", "file3.js" ]);
console.log(result.code);
To generate a source map:
var result = UglifyJS.minify([ "file1.js", "file2.js", "file3.js" ], {
outSourceMap: "out.js.map"
});
console.log(result.code); // minified output
console.log(result.map);
To generate a source map with the fromString option, you can also use an object:
var result = UglifyJS.minify({"file1.js": "var a = function () {};"}, {
outSourceMap: "out.js.map",
fromString: true
});
Note that the source map is not saved in a file, it's just returned in
result.map
. The value passed for outSourceMap
is only used to set the
file
attribute in the source map (see the spec).
You can also specify sourceRoot property to be included in source map:
var result = UglifyJS.minify([ "file1.js", "file2.js", "file3.js" ], {
outSourceMap: "out.js.map",
sourceRoot: "http://example.com/src"
});
If you're compressing compiled JavaScript and have a source map for it, you
can use the inSourceMap
argument:
var result = UglifyJS.minify("compiled.js", {
inSourceMap: "compiled.js.map",
outSourceMap: "minified.js.map"
});
// same as before, it returns `code` and `map`
If your input source map is not in a file, you can pass it in as an object
using the inSourceMap
argument:
var result = UglifyJS.minify("compiled.js", {
inSourceMap: JSON.parse(my_source_map_string),
outSourceMap: "minified.js.map"
});
The inSourceMap
is only used if you also request outSourceMap
(it makes
no sense otherwise).
To set the source map url, use the sourceMapUrl
option.
If you're using the X-SourceMap header instead, you can just set the sourceMapUrl
option to false.
Defaults to outSourceMap:
var result = UglifyJS.minify([ "file1.js" ], {
outSourceMap: "out.js.map",
sourceMapUrl: "localhost/out.js.map"
});
Other options:
warnings
(defaultfalse
) — passtrue
to display compressor warnings.fromString
(defaultfalse
) — if you passtrue
then you can pass JavaScript source code, rather than file names.mangle
(defaulttrue
) — passfalse
to skip mangling names, or pass an object to specify mangling options (see below).mangleProperties
(defaultfalse
) — pass an object to specify custom mangle property options.output
(defaultnull
) — pass an object if you wish to specify additional output options. The defaults are optimized for best compression.compress
(default{}
) — passfalse
to skip compressing entirely. Pass an object to specify custom compressor options.parse
(default {}) — pass an object if you wish to specify some additional parser options. (not all options available... see below)
mangle
except
- pass an array of identifiers that should be excluded from manglingtoplevel
— mangle names declared in the toplevel scope (disabled by default).eval
— mangle names visible in scopes where eval or with are used (disabled by default).keep_fnames
-- defaultfalse
. Passtrue
to not mangle function names. Useful for code relying onFunction.prototype.name
. See also: thekeep_fnames
compress option.
Examples:
//tst.js
var globalVar;
function funcName(firstLongName, anotherLongName)
{
var myVariable = firstLongName + anotherLongName;
}
UglifyJS.minify("tst.js").code;
// 'function funcName(a,n){}var globalVar;'
UglifyJS.minify("tst.js", { mangle: { except: ['firstLongName'] } }).code;
// 'function funcName(firstLongName,a){}var globalVar;'
UglifyJS.minify("tst.js", { mangle: { toplevel: true } }).code;
// 'function n(n,a){}var a;'
mangleProperties options
regex
— Pass a RegExp to only mangle certain names (maps to the--mangle-regex
CLI arguments option)ignore_quoted
– Only mangle unquoted property names (maps to the--mangle-props 2
CLI arguments option)
We could add more options to UglifyJS.minify
— if you need additional
functionality please suggest!
The hard way
Following there's more detailed API info, in case the minify
function is
too simple for your needs.
The parser
var toplevel_ast = UglifyJS.parse(code, options);
options
is optional and if present it must be an object. The following
properties are available:
strict
— disable automatic semicolon insertion and support for trailing comma in arrays and objectsbare_returns
— Allow return outside of functions. (maps to the--bare-returns
CLI arguments option and available tominify
parse
other options object)filename
— the name of the file where this code is coming fromtoplevel
— atoplevel
node (as returned by a previous invocation ofparse
)
The last two options are useful when you'd like to minify multiple files and get a single file as the output and a proper source map. Our CLI tool does something like this:
var toplevel = null;
files.forEach(function(file){
var code = fs.readFileSync(file, "utf8");
toplevel = UglifyJS.parse(code, {
filename: file,
toplevel: toplevel
});
});
After this, we have in toplevel
a big AST containing all our files, with
each token having proper information about where it came from.
Scope information
UglifyJS contains a scope analyzer that you need to call manually before
compressing or mangling. Basically it augments various nodes in the AST
with information about where is a name defined, how many times is a name
referenced, if it is a global or not, if a function is using eval
or the
with
statement etc. I will discuss this some place else, for now what's
important to know is that you need to call the following before doing
anything with the tree:
toplevel.figure_out_scope()
Compression
Like this:
var compressor = UglifyJS.Compressor(options);
var compressed_ast = toplevel.transform(compressor);
The options
can be missing. Available options are discussed above in
“Compressor options”. Defaults should lead to best compression in most
scripts.
The compressor is destructive, so don't rely that toplevel
remains the
original tree.
Mangling
After compression it is a good idea to call again figure_out_scope
(since
the compressor might drop unused variables / unreachable code and this might
change the number of identifiers or their position). Optionally, you can
call a trick that helps after Gzip (counting character frequency in
non-mangleable words). Example:
compressed_ast.figure_out_scope();
compressed_ast.compute_char_frequency();
compressed_ast.mangle_names();
Generating output
AST nodes have a print
method that takes an output stream. Essentially,
to generate code you do this:
var stream = UglifyJS.OutputStream(options);
compressed_ast.print(stream);
var code = stream.toString(); // this is your minified code
or, for a shortcut you can do:
var code = compressed_ast.print_to_string(options);
As usual, options
is optional. The output stream accepts a lot of options,
most of them documented above in section “Beautifier options”. The two
which we care about here are source_map
and comments
.
Keeping comments in the output
In order to keep certain comments in the output you need to pass the
comments
option. Pass a RegExp or a function. If you pass a RegExp, only
those comments whose body matches the regexp will be kept. Note that body
means without the initial //
or /*
. If you pass a function, it will be
called for every comment in the tree and will receive two arguments: the
node that the comment is attached to, and the comment token itself.
The comment token has these properties:
type
: "comment1" for single-line comments or "comment2" for multi-line commentsvalue
: the comment bodypos
andendpos
: the start/end positions (zero-based indexes) in the original code where this comment appearsline
andcol
: the line and column where this comment appears in the original codefile
— the file name of the original filenlb
— true if there was a newline before this comment in the original code, or if this comment contains a newline.
Your function should return true
to keep the comment, or a falsy value
otherwise.
Generating a source mapping
You need to pass the source_map
argument when calling print
. It needs
to be a SourceMap
object (which is a thin wrapper on top of the
source-map library).
Example:
var source_map = UglifyJS.SourceMap(source_map_options);
var stream = UglifyJS.OutputStream({
...
source_map: source_map
});
compressed_ast.print(stream);
var code = stream.toString();
var map = source_map.toString(); // json output for your source map
The source_map_options
(optional) can contain the following properties:
file
: the name of the JavaScript output file that this mapping refers toroot
: thesourceRoot
property (see the spec)orig
: the "original source map", handy when you compress generated JS and want to map the minified output back to the original code where it came from. It can be simply a string in JSON, or a JSON object containing the original source map.