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).
uglify-js
only supports ECMAScript 5 (ES5).const
is present but incomplete, and may not be transformed properly.npm
package uglify-es.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
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. --source-map-inline Write base64-encoded source map to the end of js output. --in-source-map 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 inline with the sources. --screw-ie8 Use this flag if you don't wish to support Internet Explorer 6/7/8. By default UglifyJS will not try to be IE-proof. --support-ie8 Use this flag to support Internet Explorer 6/7/8. Equivalent to setting `screw_ie8: false` in `minify()` for `compress`, `mangle` and `output` options. --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, e.g. `-c 'if_return=false,pure_funcs=["Math.pow","console.log"]'` Use `-c` with no argument to enable 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 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. --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 Functions that can be safely removed if their return value is not used, e.g. `--pure-funcs Math.floor console.info` (requires `--compress`)
Specify --output
(-o
) to declare the output file. Otherwise the output goes to STDOUT.
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
).
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
or --in-source-map inline
if the source map is included inline with the sources. 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.
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 where eval
or with
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
)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.
--mangle-props=unquoted
or --mangle-props=2
)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:
$ echo 'var o={"foo":1, bar:3}; o.foo += o.bar; console.log(o.foo);' | uglifyjs --mangle-props=2 -mc var o={"foo":1,a:3};o.foo+=o.a,console.log(o.foo);
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.
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.
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 to true
then the default sequences
limit is 200
. Set option to false
or 0
to disable. The smallest sequences
length is 2
. A sequences
value of 1
is grandfathered to be equivalent to true
and as such means 200
. On rare occasions the default sequences limit leads to very slow compress times in which case a value of 20
or less is recommended.
properties
-- rewrite property access using the dot notation, for example foo["bar"] → foo.bar
dead_code
-- remove unreachable code
drop_debugger
-- remove debugger;
statements
unsafe
(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 like get
, or valueOf
. This could cause change in execution order after operands in the comparison are switching. Compression only works if both comparisons
and unsafe_comps
are both set to true.
unsafe_math
(default: false) -- optimize numerical expressions like 2 * x * 3
into 6 * x
, which may give imprecise floating point results.
unsafe_proto
(default: false) -- optimize expressions like Array.prototype.slice.call(a)
into [].slice.call(a)
unsafe_regexp
(default: false) -- enable substitutions of variables with RegExp
values the same way as if they are constants.
conditionals
-- apply optimizations for if
-s and conditional expressions
comparisons
-- apply certain optimizations to binary nodes, for example: !(a <= b) → a > b
(only when unsafe_comps
), attempts to negate binary nodes, e.g. a = !b && !c && !d && !e → a=!(b||c||d||e)
etc.
evaluate
-- attempt to evaluate constant expressions
booleans
-- various optimizations for boolean context, for example !!a ? b : c → a ? b : c
loops
-- optimizations for do
, while
and for
loops when we can statically determine the condition
unused
-- drop unreferenced functions and variables (simple direct variable assignments do not count as references unless set to "keep_assign"
)
toplevel
-- drop unreferenced functions ("funcs"
) and/or variables ("vars"
) in the toplevel scope (false
by default, true
to drop both unreferenced functions and variables)
top_retain
-- prevent specific toplevel functions and variables from unused
removal (can be array, comma-separated, RegExp or function. Implies toplevel
)
hoist_funs
-- hoist function declarations
hoist_vars
(default: false) -- hoist var
declarations (this is false
by default because it seems to increase the size of the output in general)
if_return
-- optimizations for if/return and if/continue
join_vars
-- join consecutive var
statements
cascade
-- small optimization for sequences, transform x, x
into x
and x = something(), x
into x = something()
collapse_vars
-- Collapse single-use var
and const
definitions when possible.
reduce_vars
-- Improve optimization on variables assigned with and used as constant values.
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 is false
. If you pass true
for this, UglifyJS will assume that object property access (e.g. foo.bar
or foo["bar"]
) doesn't have any side effects. Specify "strict"
to treat foo.bar
as side-effect-free only when foo
is certain to not throw, i.e. not null
or undefined
.
pure_funcs
-- default null
. 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 instance var q = Math.floor(a/b)
. If variable q
is not used elsewhere, UglifyJS will drop it, but will still keep the Math.floor(a/b)
, not knowing what it does. You can pass pure_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
-- default false
. Pass true
to discard calls to console.*
functions. If you wish to drop a specific function call such as console.info
and/or retain side effects from function arguments after dropping the function call then use pure_funcs
instead.
expression
-- default false
. Pass true
to preserve completion values from terminal statements without return
, e.g. in bookmarklets.
keep_fargs
-- default true
. Prevents the compressor from discarding unused function arguments. You need this for code which relies on Function.length
.
keep_fnames
-- default false
. Pass true
to prevent the compressor from discarding function names. Useful for code relying on Function.prototype.name
. See also: the keep_fnames
mangle option.
passes
-- default 1
. Number of times to run compress with a maximum of 3. In some cases more than one pass leads to further compressed code. Keep in mind more passes will take more time.
keep_infinity
-- default false
. Pass true
to prevent Infinity
from being compressed into 1/0
, which may cause performance issues on Chrome.
side_effects
-- default true
. Pass false
to disable potentially dropping functions marked as “pure”. A function call is marked as “pure” if a comment annotation /*@__PURE__*/
or /*#__PURE__*/
immediately precedes the call. For example: /*@__PURE__*/foo();
unsafe
optionIt 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)
or Array(1, 2, 3)
→ [ 1, 2, 3 ]
new Object()
→ {}
String(exp)
or exp.toString()
→ "" + exp
new Object/RegExp/Function/Error/Array (...)
→ we discard the new
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)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"); }
You can specify nested constants in the form of --define env.DEBUG=false
.
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; // 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 which does not support const
, using var
with reduce_vars
(enabled by default) should suffice.
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 } } });
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
(default true
) -- 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
(default false
) -- pass true
to quote all keys in literal objectsspace-colon
(default true
) -- insert a space after the colon signsascii-only
(default false
) -- escape Unicode characters in strings and regexps (affects directives with non-ascii characters becoming invalid)inline-script
(default false
) -- 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
(default false
) -- always insert brackets in if
, for
, do
, while
or with
statements, even if their body is a single statement.semicolons
(default true
) -- separate statements with semicolons. If you pass false
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
(default null
) -- 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
(default 0
) -- 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 quoteskeep_quoted_props
(default false
) -- when turned on, prevents stripping quotes from property names in object literals.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.
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.
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.
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 = UglifyJS.Compressor(options).compress(uAST); // 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.
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.
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", outFileName: "out.js", 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 //# sourceMappingURL=out.js.map
in result.code
. The value of outFileName
is only used to set file
attribute in source map file.
The file
attribute in the source map (see the spec) will use outFileName
firstly, if it's falsy, then will be deduced from outSourceMap
(by removing '.map'
).
You can set option sourceMapInline
to be true
and source map will be appended to code.
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
(default false
) — pass true
to display compressor warnings.
fromString
(default false
) — if you pass true
then you can pass JavaScript source code, rather than file names.
mangle
(default true
) — pass false
to skip mangling names, or pass an object to specify mangling options (see below).
mangleProperties
(default false
) — pass an object to specify custom mangle property options.
output
(default null
) — pass an object if you wish to specify additional output options. The defaults are optimized for best compression.
compress
(default {}
) — pass false
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)
except
- pass an array of identifiers that should be excluded from mangling
toplevel
— 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
-- default false
. Pass true
to not mangle function names. Useful for code relying on Function.prototype.name
. See also: the keep_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;'
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)debug
– Mangle names with the original name still present (maps to the --mangle-props-debug
CLI arguments option). Defaults to false
. Pass an empty string to enable, or a non-empty string to set the suffix.We could add more options to UglifyJS.minify
— if you need additional functionality please suggest!
Following there's more detailed API info, in case the minify
function is too simple for your needs.
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 to minify
parse
other options object)filename
— the name of the file where this code is coming fromtoplevel
— a toplevel
node (as returned by a previous invocation of parse
)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.
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()
Like this:
var compressor = UglifyJS.Compressor(options); var compressed_ast = compressor.compress(toplevel);
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.
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();
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
.
In order to keep certain comments in the output you need to pass the comments
option. Pass a RegExp (as string starting and closing with /
or pass a RegExp object), a boolean or a function. Stringified options all
and some
can be passed too, where some
behaves like it's cli equivalent --comments
without passing a value. 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
and endpos
: the start/end positions (zero-based indexes) in the original code where this comment appearsline
and col
: 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.
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 to
root
: the sourceRoot
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.
const
const
in uglify-js@2.x
has function scope and as such behaves much like var
- unlike const
in ES2015 (ES6) which has block scope. It is recommended to avoid using const
for this reason as it will have undefined behavior when run on an ES2015 compatible browser.