UglifyJS 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 no input file is specified, UglifyJS 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:

uglifyjs --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.
                                `debug`  Add debug prefix and suffix.
                                `domprops`  Mangle property names that overlaps
                                            with DOM properties.
                                `keep_quoted`  Only mangle unquoted properties.
                                `regex`  Only mangle matched property names.
                                `reserved`  List of names that should not be mangled.
    -b, --beautify [options]    Beautify output/specify output options:
                                `beautify`  Enabled with `--beautify` by default.
                                `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 UglifyJS 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.
    --ie8                       Support non-standard Internet Explorer 8.
                                Equivalent to setting `ie8: true` in `minify()`
                                for `compress`, `mangle` and `output` options.
                                By default UglifyJS 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.
    --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 `uglify-es` will not work around
                                Safari 10/11 bugs.
    --self                      Build UglifyJS as a library (implies --wrap UglifyJS)
    --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

UglifyJS 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 UglifyJS assumes HTTP X-SourceMap is being used and will omit the //# sourceMappingURL= directive.

For example:

uglifyjs 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). 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 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:

uglifyjs 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 (default false) -- mangle names declared in the top level scope.
eval (default false) -- mangle names visible in scopes where eval or with 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:

uglifyjs ... -m reserved=['
to prevent the require, exports and $ names from being changed.
CLI mangling property names (--mangle-props)
Note: THIS WILL PROBABLY BREAK YOUR CODE.  Mangling property names
is a separate step, different from variable name mangling.  Pass
--mangle-props to enable it.  It will mangle all properties in the
input code with the exception of built in DOM properties and properties
in core JavaScript classes.  For 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):
$ uglifyjs 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:
$ uglifyjs 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:
$ uglifyjs 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:
$ uglifyjs 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 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.
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);
$ uglifyjs 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.
$ uglifyjs 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.
API Reference
Assuming installation via NPM, you can load UglifyJS in your application
like this:
var UglifyJS = require("uglify-es");
There is a single high level function, minify(code, options),
which will perform all minification phases in a configurable
manner. By default minify() will enable the options compress
and mangle. Example:
var code = "function add(first, second) { return first + second; }";
var result = UglifyJS.minify(code);
console.log(result.error); // runtime error, or `undefined` if no error
console.log(result.code);  // minified output: function add(n,d){return n+d}
You can minify more than one JavaScript file at a time by using an object
for the first argument where the keys are file names and the values are source
code:
var code = {
    "file1.js": "function add(first, second) { return first + second; }",
    "file2.js": "console.log(add(1 + 2, 3 + 4));"
};
var result = UglifyJS.minify(code);
console.log(result.code);
// function add(d,n){return d+n}console.log(add(3,7));
The toplevel option:
var code = {
    "file1.js": "function add(first, second) { return first + second; }",
    "file2.js": "console.log(add(1 + 2, 3 + 4));"
};
var options = { toplevel: true };
var result = UglifyJS.minify(code, options);
console.log(result.code);
// console.log(3+7);
The nameCache option:
var options = {
    mangle: {
        toplevel: true,
    },
    nameCache: {}
};
var result1 = UglifyJS.minify({
    "file1.js": "function add(first, second) { return first + second; }"
}, options);
var result2 = UglifyJS.minify({
    "file2.js": "console.log(add(1 + 2, 3 + 4));"
}, options);
console.log(result1.code);
// function n(n,r){return n+r}
console.log(result2.code);
// console.log(n(3,7));
You may persist the name cache to the file system in the following way:
var cacheFileName = "/tmp/cache.json";
var options = {
    mangle: {
        properties: true,
    },
    nameCache: JSON.parse(fs.readFileSync(cacheFileName, "utf8"))
};
fs.writeFileSync("part1.js", UglifyJS.minify({
    "file1.js": fs.readFileSync("file1.js", "utf8"),
    "file2.js": fs.readFileSync("file2.js", "utf8")
}, options).code, "utf8");
fs.writeFileSync("part2.js", UglifyJS.minify({
    "file3.js": fs.readFileSync("file3.js", "utf8"),
    "file4.js": fs.readFileSync("file4.js", "utf8")
}, options).code, "utf8");
fs.writeFileSync(cacheFileName, JSON.stringify(options.nameCache), "utf8");
An example of a combination of minify() options:
var code = {
    "file1.js": "function add(first, second) { return first + second; }",
    "file2.js": "console.log(add(1 + 2, 3 + 4));"
};
var options = {
    toplevel: true,
    compress: {
        global_defs: {
            "@console.log": "alert"
        },
        passes: 2
    },
    output: {
        beautify: false,
        preamble: "/* uglified */"
    }
};
var result = UglifyJS.minify(code, options);
console.log(result.code);
// /* uglified */
// alert(10);"
To produce warnings:
var code = "function f(){ var u; return 2 + 3; }";
var options = { warnings: true };
var result = UglifyJS.minify(code, options);
console.log(result.error);    // runtime error, `undefined` in this case
console.log(result.warnings); // [ 'Dropping unused variable u [0:1,18]' ]
console.log(result.code);     // function f(){return 5}
An error example:
var result = UglifyJS.minify({"foo.js" : "if (0) else console.log(1);"});
console.log(JSON.stringify(result.error));
// {"message":"Unexpected token: keyword (else)","filename":"foo.js","line":1,"col":7,"pos":7}
Note: unlike uglify-js@2.x, the 3.x API does not throw errors. To
achieve a similar effect one could do the following:
var result = UglifyJS.minify(code, options);
if (result.error) throw result.error;
Minify options

ecma (default undefined) - pass 5, 6, 7 or 8 to override parse,
compress and output options.

warnings (default false) — pass true to return compressor warnings
in result.warnings. Use the value "verbose" for more detailed warnings.

parse (default {}) — pass an object if you wish to specify some
additional parse options.

compress (default {}) — pass false to skip compressing entirely.
Pass an object to specify custom compress options.

mangle (default true) — pass false to skip mangling names, or pass
an object to specify mangle options (see below).

mangle.properties (default false) — a subcategory of the mangle option.
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.

sourceMap (default false) - pass an object if you wish to specify
source map options.

toplevel (default false) - set to true if you wish to enable top level
variable and function name mangling and to drop unused variables and functions.

nameCache (default null) - pass an empty object {} or a previously
used nameCache object if you wish to cache mangled variable and
property names across multiple invocations of minify(). Note: this is
a read/write property. minify() will read the name cache state of this
object and update it during minification so that it may be
reused or externally persisted by the user.

ie8 (default false) - set to true to support IE8.

keep_classnames (default: undefined) - pass true to prevent discarding or mangling
of class names.

keep_fnames (default: false) - pass true to prevent discarding or mangling
of function names.  Useful for code relying on Function.prototype.name. If the
top level minify option keep_classnames is undefined it will be overriden with
the value of the top level minify option keep_fnames.

safari10 (default: false) - pass true to work around Safari 10/11 bugs in
loop scoping and await. See safari10 options in mangle
and output for details.


Minify options structure
{
    parse: {
        // parse options
    },
    compress: {
        // compress options
    },
    mangle: {
        // mangle options

        properties: {
            // mangle property options
        }
    },
    output: {
        // output options
    },
    sourceMap: {
        // source map options
    },
    ecma: 5, // specify one of: 5, 6, 7 or 8
    keep_classnames: false,
    keep_fnames: false,
    ie8: false,
    nameCache: null, // or specify a name cache object
    safari10: false,
    toplevel: false,
    warnings: false,
}
Source map options
To generate a source map:
var result = UglifyJS.minify({"file1.js": "var a = function() {};"}, {
    sourceMap: {
        filename: "out.js",
        url: "out.js.map"
    }
});
console.log(result.code); // minified output
console.log(result.map);  // source map
Note that the source map is not saved in a file, it's just returned in
result.map.  The value passed for sourceMap.url is only used to set
//# sourceMappingURL=out.js.map in result.code. The value of
filename is only used to set file attribute (see the spec)
in source map file.
You can set option sourceMap.url to be "inline" 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": "var a = function() {};"}, {
    sourceMap: {
        root: "http://example.com/src",
        url: "out.js.map"
    }
});
If you're compressing compiled JavaScript and have a source map for it, you
can use sourceMap.content:
var result = UglifyJS.minify({"compiled.js": "compiled code"}, {
    sourceMap: {
        content: "content from compiled.js.map",
        url: "minified.js.map"
    }
});
// same as before, it returns `code` and `map`
If you're using the X-SourceMap header instead, you can just omit sourceMap.url.
Parse options

bare_returns (default false) -- support top level return statements

ecma (default: 8) -- specify one of 5, 6, 7 or 8. Note: this setting
is not presently enforced except for ES8 optional trailing commas in function
parameter lists and calls with ecma 8.

html5_comments (default true)

shebang (default true) -- support #!command as the first line


Compress options

arrows (default: true) -- Converts ()=>{return x} to ()=>x. Class
and object literal methods will also be converted to arrow expressions if
the resultant code is shorter: m(){return x} becomes m:()=>x.
This transform requires that the ecma compress option is set to 6 or greater.

booleans (default: true) -- various optimizations for boolean context,
for example !!a ? b : c → a ? b : c

collapse_vars (default: true) -- Collapse single-use non-constant variables,
side effects permitting.

comparisons (default: true) -- apply certain optimizations to binary nodes,
e.g. !(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.

computed_props (default: true) -- Transforms constant computed properties
into regular ones: {["computed"]: 1} is converted to {computed: 1}.

conditionals (default: true) -- apply optimizations for if-s and conditional
expressions

dead_code (default: true) -- remove unreachable code

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.

drop_debugger (default: true) -- remove debugger; statements

ecma (default: 5) -- Pass 6 or greater to enable compress options that
will transform ES5 code into smaller ES6+ equivalent forms.

evaluate (default: true) -- attempt to evaluate constant expressions

expression (default: false) -- Pass true to preserve completion values
from terminal statements without return, e.g. in bookmarklets.

global_defs (default: {}) -- see conditional compilation

hoist_funs (default: false) -- hoist function declarations

hoist_props (default: true) -- hoist properties from constant object and
array literals into regular variables subject to a set of constraints. For example:
var o={p:1, q:2}; f(o.p, o.q); is converted to f(1, 2);. Note: hoist_props
works best with mangle enabled, the compress option passes set to 2 or higher,
and the compress option toplevel enabled.

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 (default: true) -- optimizations for if/return and if/continue

inline (default: true) -- inline calls to function with simple/return statement:

false -- same as 0
0 -- disabled inlining
1 -- inline simple functions
2 -- inline functions with arguments
3 -- inline functions with arguments and variables
true -- same as 3


join_vars (default: true) -- join consecutive var statements

keep_classnames (default: false) -- Pass true to prevent the
compressor from discarding class names.  See also: the keep_classnames
mangle option.

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.

keep_infinity (default: false) -- Pass true to prevent Infinity from
being compressed into 1/0, which may cause performance issues on Chrome.

loops (default: true) -- optimizations for do, while and for loops
when we can statically determine the condition.

negate_iife (default: true) -- negate "Immediately-Called Function Expressions"
where the return value is discarded, to avoid the parens that the
code generator would insert.

passes (default: 1) -- The maximum number of times to run compress.
In some cases more than one pass leads to further compressed code.  Keep in
mind more passes will take more time.

properties (default: true) -- rewrite property access using the dot notation, for
example foo["bar"] → foo.bar

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).

pure_getters (default: "strict") -- 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.

reduce_funcs (default: true) -- Allows single-use functions to be
inlined as function expressions when permissible allowing further
optimization.  Enabled by default.  Option depends on reduce_vars
being enabled.  Some code runs faster in the Chrome V8 engine if this
option is disabled.  Does not negatively impact other major browsers.

reduce_vars (default: true) -- Improve optimization on variables assigned with and
used as constant values.

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.

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();

switches (default: true) -- de-duplicate and remove unreachable switch branches

toplevel (default: false) -- drop unreferenced functions ("funcs") and/or
variables ("vars") in the top level scope (false by default, true to drop
both unreferenced functions and variables)

top_retain (default: null) -- prevent specific toplevel functions and
variables from unused removal (can be array, comma-separated, RegExp or
function. Implies toplevel)

typeofs (default: true) -- Transforms typeof foo == "undefined" into
foo === void 0.  Note: recommend to set this value to false for IE10 and
earlier versions due to known issues.

unsafe (default: false) -- apply "unsafe" transformations (discussion below)

unsafe_arrows (default: false) -- Convert ES5 style anonymous function
expressions to arrow functions if the function body does not reference this.
Note: it is not always safe to perform this conversion if code relies on the
the function having a prototype, which arrow functions lack.
This transform requires that the ecma compress option is set to 6 or greater.

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_Function (default: false) -- compress and mangle Function(args, code)
when both args and code are string literals.

unsafe_math (default: false) -- optimize numerical expressions like
2 * x * 3 into 6 * x, which may give imprecise floating point results.

unsafe_methods (default: false) -- Converts { m: function(){} } to
{ m(){} }. ecma must be set to 6 or greater to enable this transform.
If unsafe_methods is a RegExp then key/value pairs with keys matching the
RegExp will be converted to concise methods.
Note: if enabled there is a risk of getting a "<method name> is not a
constructor" TypeError should any code try to new the former function.

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.

unsafe_undefined (default: false) -- substitute void 0 if there is a
variable named undefined in scope (variable name will be mangled, typically
reduced to a single character)

unused (default: true) -- drop unreferenced functions and variables (simple
direct variable assignments do not count as references unless set to "keep_assign")

warnings (default: false) -- display warnings when dropping unreachable
code or unused declarations etc.


Mangle options

eval (default false) -- Pass true to mangle names visible in scopes
where eval or with are used.

keep_classnames (default false) -- Pass true to not mangle class names.
See also: the keep_classnames compress option.

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.

reserved (default []) -- Pass an array of identifiers that should be
excluded from mangling. Example: ["foo", "bar"].

toplevel (default false) -- Pass true to mangle names declared in the
top level scope.

safari10 (default false) -- Pass true to work around the Safari 10 loop
iterator bug
"Cannot declare a let variable twice".
See also: the safari10 output option.


Examples:
// test.js
var globalVar;
function funcName(firstLongName, anotherLongName) {
    var myVariable = firstLongName +  anotherLongName;
}
var code = fs.readFileSync("test.js", "utf8");

UglifyJS.minify(code).code;
// 'function funcName(a,n){}var globalVar;'

UglifyJS.minify(code, { mangle: { reserved: ['firstLongName'] } }).code;
// 'function funcName(firstLongName,a){}var globalVar;'

UglifyJS.minify(code, { mangle: { toplevel: true } }).code;
// 'function n(n,a){}var a;'
Mangle properties options

builtins (default: false) -- Use true to allow the mangling of builtin
DOM properties. Not recommended to override this setting.

debug (default: false) -— Mangle names with the original name still present.
Pass an empty string "" to enable, or a non-empty string to set the debug suffix.

keep_quoted (default: false) -— Only mangle unquoted property names.

regex (default: null) -— Pass a RegExp literal to only mangle property
names matching the regular expression.

reserved (default: []) -- Do not mangle property names listed in the
reserved array.


Output 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:

ascii_only (default false) -- escape Unicode characters in strings and
regexps (affects directives with non-ascii characters becoming invalid)

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.

bracketize (default false) -- always insert brackets in if, for,
do, while or with statements, even if their body is a single
statement.

comments (default false) -- pass true or "all" to preserve all
comments, "some" to preserve some comments, a regular expression string
(e.g. /^!/) or a function.

ecma (default 5) -- set output printing mode. Set ecma to 6 or
greater to emit shorthand object properties - i.e.: {a} instead of {a: a}.
The ecma option will only change the output in direct control of the
beautifier. Non-compatible features in the abstract syntax tree will still
be output as is. For example: an ecma setting of 5 will not convert
ES6+ code to ES5.

indent_level (default 4)

indent_start (default 0) -- prefix all lines by that many spaces

inline_script (default false) -- escape the slash in occurrences of
</script in strings

keep_quoted_props (default false) -- when turned on, prevents stripping
quotes from property names in object literals.

max_line_len (default false) -- maximum line length (for uglified code)

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.

preserve_line (default false) -- pass true to preserve lines, but it
only works if beautify is set to false.

quote_keys (default false) -- pass true to quote all keys in literal
objects

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. 0 is best for gzip size.
1 -- always use single quotes
2 -- always use double quotes
3 -- always use the original quotes


safari10 (default false) -- set this option to true to work around
the Safari 10/11 await bug.
See also: the safari10 mangle option.

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).

shebang (default true) -- preserve shebang #! in preamble (bash scripts)

webkit (default false) -- enable workarounds for WebKit bugs.
PhantomJS users should set this option to true.

width (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.

wrap_iife (default false) -- pass true to wrap immediately invoked
function expressions. See
#640 for more details.


Miscellaneous
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 /^!/
will keep comments like /*! Copyright Notice */.
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.
The unsafe compress option
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) 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

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");
}
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:
var DEBUG = false;
var 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.
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:
var result = UglifyJS.minify(fs.readFileSync("input.js", "utf8"), {
    compress: {
        dead_code: true,
        global_defs: {
            DEBUG: false
        }
    }
});
To replace an identifier with an arbitrary non-constant expression it is
necessary to prefix the global_defs key with "@" to instruct UglifyJS
to parse the value as an expression:
UglifyJS.minify("alert('hello');", {
    compress: {
        global_defs: {
            "@alert": "console.log"
        }
    }
}).code;
// returns: 'console.log("hello");'
Otherwise it would be replaced as string literal:
UglifyJS.minify("alert('hello');", {
    compress: {
        global_defs: {
            "alert": "console.log"
        }
    }
}).code;
// returns: '"console.log"("hello");'
Using native Uglify AST with minify()
// example: parse only, produce native Uglify AST

var result = UglifyJS.minify(code, {
    parse: {},
    compress: false,
    mangle: false,
    output: {
        ast: true,
        code: false  // optional - faster if false
    }
});

// result.ast contains native Uglify AST
// example: accept native Uglify AST input and then compress and mangle
//          to produce both code and native AST.

var result = UglifyJS.minify(ast, {
    compress: {},
    mangle: {},
    output: {
        ast: true,
        code: true  // optional - faster if false
    }
});

// result.ast contains native Uglify AST
// result.code contains the minified code in string form.
Working with Uglify AST
Transversal and transformation of the native AST can be performed through
TreeWalker and
TreeTransformer respectively.
ESTree / SpiderMonkey AST
UglifyJS 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 -p spidermonkey -m -c
The -p 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 -p 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.
Uglify Fast Minify Mode
It's not well known, but whitespace removal and symbol mangling accounts
for 95% of the size reduction in minified code for most JavaScript - not
elaborate code transforms. One can simply disable compress to speed up
Uglify builds by 3 to 4 times. In this fast mangle-only mode Uglify has
comparable minify speeds and gzip sizes to
butternut:



d3.js
minify size
gzip size
minify time (seconds)



original
451,131
108,733
-


uglify-js@3.0.24 mangle=false, compress=false
316,600
85,245
0.70


uglify-js@3.0.24 mangle=true, compress=false
220,216
72,730
1.13


butternut@0.4.6
217,568
72,738
1.41


uglify-js@3.0.24 mangle=true, compress=true
212,511
71,560
3.36


babili@0.1.4
210,713
72,140
12.64


To enable fast minify mode from the CLI use:
uglifyjs file.js -m
To enable fast minify mode with the API use:
UglifyJS.minify(code, { compress: false, mangle: true });
,'require','exports']

to prevent the __INLINE_CODE_39__, __INLINE_CODE_40__ and __INLINE_CODE_41__ names from being changed.

CLI mangling property names (__INLINE_CODE_42__)

Note: THIS WILL PROBABLY BREAK YOUR CODE. Mangling property names is a separate step, different from variable name mangling. Pass __INLINE_CODE_43__ to enable it. It will mangle all properties in the input code with the exception of built in DOM properties and properties in core JavaScript classes. For example:

__CODE_BLOCK_8__

Mangle all properties (except for JavaScript __INLINE_CODE_44__):

__CODE_BLOCK_9__ __CODE_BLOCK_10__

Mangle all properties except for __INLINE_CODE_45__ properties:

__CODE_BLOCK_11__ __CODE_BLOCK_12__

Mangle all properties matching a __INLINE_CODE_46__:

__CODE_BLOCK_13__ __CODE_BLOCK_14__

Combining mangle properties options:

__CODE_BLOCK_15__ __CODE_BLOCK_16__

In order for this to be of any use, we avoid mangling standard JS names by default (__INLINE_CODE_47__ to override).

A default exclusion file is provided in __INLINE_CODE_48__ which should cover most standard JS and DOM properties defined in various browsers. Pass __INLINE_CODE_49__ to disable this feature.

A regular expression can be used to define which property names should be mangled. For example, __INLINE_CODE_50__ 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 __INLINE_CODE_51__ and UglifyJS will maintain these mappings in a file which can then be reused. It should be initially empty. Example:

__CODE_BLOCK_17__

Now, __INLINE_CODE_52__ and __INLINE_CODE_53__ 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.

Mangling unquoted names (__INLINE_CODE_54__)

Using quoted property name (__INLINE_CODE_55__) reserves the property name (__INLINE_CODE_56__) so that it is not mangled throughout the entire script even when used in an unquoted style (__INLINE_CODE_57__). Example:

__CODE_BLOCK_18__ __CODE_BLOCK_19__ __CODE_BLOCK_20__

Debugging property name mangling

You can also pass __INLINE_CODE_58__ in order to mangle property names without completely obscuring them. For example the property __INLINE_CODE_59__ would mangle to __INLINE_CODE_60__ 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.

__CODE_BLOCK_21__ __CODE_BLOCK_22__

You can also pass a custom suffix using __INLINE_CODE_61__. This would then mangle __INLINE_CODE_62__ to __INLINE_CODE_63__. 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.

API Reference

Assuming installation via NPM, you can load UglifyJS in your application like this:

__CODE_BLOCK_23__

There is a single high level function, __INLINE_CODE_64__, which will perform all minification phases in a configurable manner. By default __INLINE_CODE_65__ will enable the options __INLINE_CODE_66__ and __INLINE_CODE_67__. Example:

__CODE_BLOCK_24__

You can __INLINE_CODE_68__ more than one JavaScript file at a time by using an object for the first argument where the keys are file names and the values are source code:

__CODE_BLOCK_25__

The __INLINE_CODE_69__ option:

__CODE_BLOCK_26__

The __INLINE_CODE_70__ option:

__CODE_BLOCK_27__

You may persist the name cache to the file system in the following way:

__CODE_BLOCK_28__

An example of a combination of __INLINE_CODE_71__ options:

__CODE_BLOCK_29__

To produce warnings:

__CODE_BLOCK_30__

An error example:

__CODE_BLOCK_31__

Note: unlike __INLINE_CODE_72__, the __INLINE_CODE_73__ API does not throw errors. To achieve a similar effect one could do the following:

__CODE_BLOCK_32__

Minify options

__INLINE_CODE_74__ (default __INLINE_CODE_75__) - pass __INLINE_CODE_76__, __INLINE_CODE_77__, __INLINE_CODE_78__ or __INLINE_CODE_79__ to override __INLINE_CODE_80__, __INLINE_CODE_81__ and __INLINE_CODE_82__ options.
__INLINE_CODE_83__ (default __INLINE_CODE_84__) — pass __INLINE_CODE_85__ to return compressor warnings in __INLINE_CODE_86__. Use the value __INLINE_CODE_87__ for more detailed warnings.
__INLINE_CODE_88__ (default __INLINE_CODE_89__) — pass an object if you wish to specify some additional parse options.
__INLINE_CODE_90__ (default __INLINE_CODE_91__) — pass __INLINE_CODE_92__ to skip compressing entirely. Pass an object to specify custom compress options.
__INLINE_CODE_93__ (default __INLINE_CODE_94__) — pass __INLINE_CODE_95__ to skip mangling names, or pass an object to specify mangle options (see below).
- __INLINE_CODE_96__ (default __INLINE_CODE_97__) — a subcategory of the mangle option. Pass an object to specify custom mangle property options.
__INLINE_CODE_98__ (default __INLINE_CODE_99__) — pass an object if you wish to specify additional output options. The defaults are optimized for best compression.
__INLINE_CODE_100__ (default __INLINE_CODE_101__) - pass an object if you wish to specify source map options.
__INLINE_CODE_102__ (default __INLINE_CODE_103__) - set to __INLINE_CODE_104__ if you wish to enable top level variable and function name mangling and to drop unused variables and functions.
__INLINE_CODE_105__ (default __INLINE_CODE_106__) - pass an empty object __INLINE_CODE_107__ or a previously used __INLINE_CODE_108__ object if you wish to cache mangled variable and property names across multiple invocations of __INLINE_CODE_109__. Note: this is a read/write property. __INLINE_CODE_110__ will read the name cache state of this object and update it during minification so that it may be reused or externally persisted by the user.
__INLINE_CODE_111__ (default __INLINE_CODE_112__) - set to __INLINE_CODE_113__ to support IE8.
__INLINE_CODE_114__ (default: __INLINE_CODE_115__) - pass __INLINE_CODE_116__ to prevent discarding or mangling of class names.
__INLINE_CODE_117__ (default: __INLINE_CODE_118__) - pass __INLINE_CODE_119__ to prevent discarding or mangling of function names. Useful for code relying on __INLINE_CODE_120__. If the top level minify option __INLINE_CODE_121__ is __INLINE_CODE_122__ it will be overriden with the value of the top level minify option __INLINE_CODE_123__.
__INLINE_CODE_124__ (default: __INLINE_CODE_125__) - pass __INLINE_CODE_126__ to work around Safari 10/11 bugs in loop scoping and __INLINE_CODE_127__. See __INLINE_CODE_128__ options in __INLINE_CODE_129__ and __INLINE_CODE_130__ for details.

Minify options structure

__CODE_BLOCK_33__

Source map options

To generate a source map:

__CODE_BLOCK_34__

Note that the source map is not saved in a file, it's just returned in __INLINE_CODE_131__. The value passed for __INLINE_CODE_132__ is only used to set __INLINE_CODE_133__ in __INLINE_CODE_134__. The value of __INLINE_CODE_135__ is only used to set __INLINE_CODE_136__ attribute (see the spec) in source map file.

You can set option __INLINE_CODE_137__ to be __INLINE_CODE_138__ and source map will be appended to code.

You can also specify sourceRoot property to be included in source map:

__CODE_BLOCK_35__

If you're compressing compiled JavaScript and have a source map for it, you can use __INLINE_CODE_139__:

__CODE_BLOCK_36__

If you're using the __INLINE_CODE_140__ header instead, you can just omit __INLINE_CODE_141__.

Parse options

__INLINE_CODE_142__ (default __INLINE_CODE_143__) -- support top level __INLINE_CODE_144__ statements
__INLINE_CODE_145__ (default: __INLINE_CODE_146__) -- specify one of __INLINE_CODE_147__, __INLINE_CODE_148__, __INLINE_CODE_149__ or __INLINE_CODE_150__. Note: this setting is not presently enforced except for ES8 optional trailing commas in function parameter lists and calls with __INLINE_CODE_151__ __INLINE_CODE_152__.
__INLINE_CODE_153__ (default __INLINE_CODE_154__)
__INLINE_CODE_155__ (default __INLINE_CODE_156__) -- support __INLINE_CODE_157__ as the first line

Compress options

__INLINE_CODE_158__ (default: __INLINE_CODE_159__) -- Converts __INLINE_CODE_160__ to __INLINE_CODE_161__. Class and object literal methods will also be converted to arrow expressions if the resultant code is shorter: __INLINE_CODE_162__ becomes __INLINE_CODE_163__. This transform requires that the __INLINE_CODE_164__ compress option is set to __INLINE_CODE_165__ or greater.
__INLINE_CODE_166__ (default: __INLINE_CODE_167__) -- various optimizations for boolean context, for example __INLINE_CODE_168__
__INLINE_CODE_169__ (default: __INLINE_CODE_170__) -- Collapse single-use non-constant variables, side effects permitting.
__INLINE_CODE_171__ (default: __INLINE_CODE_172__) -- apply certain optimizations to binary nodes, e.g. __INLINE_CODE_173__ (only when __INLINE_CODE_174__), attempts to negate binary nodes, e.g. __INLINE_CODE_175__ etc.
__INLINE_CODE_176__ (default: __INLINE_CODE_177__) -- Transforms constant computed properties into regular ones: __INLINE_CODE_178__ is converted to __INLINE_CODE_179__.
__INLINE_CODE_180__ (default: __INLINE_CODE_181__) -- apply optimizations for __INLINE_CODE_182__-s and conditional expressions
__INLINE_CODE_183__ (default: __INLINE_CODE_184__) -- remove unreachable code
__INLINE_CODE_185__ (default: __INLINE_CODE_186__) -- Pass __INLINE_CODE_187__ to discard calls to __INLINE_CODE_188__ functions. If you wish to drop a specific function call such as __INLINE_CODE_189__ and/or retain side effects from function arguments after dropping the function call then use __INLINE_CODE_190__ instead.
__INLINE_CODE_191__ (default: __INLINE_CODE_192__) -- remove __INLINE_CODE_193__ statements
__INLINE_CODE_194__ (default: __INLINE_CODE_195__) -- Pass __INLINE_CODE_196__ or greater to enable __INLINE_CODE_197__ options that will transform ES5 code into smaller ES6+ equivalent forms.
__INLINE_CODE_198__ (default: __INLINE_CODE_199__) -- attempt to evaluate constant expressions
__INLINE_CODE_200__ (default: __INLINE_CODE_201__) -- Pass __INLINE_CODE_202__ to preserve completion values from terminal statements without __INLINE_CODE_203__, e.g. in bookmarklets.
__INLINE_CODE_204__ (default: __INLINE_CODE_205__) -- see conditional compilation
__INLINE_CODE_206__ (default: __INLINE_CODE_207__) -- hoist function declarations
__INLINE_CODE_208__ (default: __INLINE_CODE_209__) -- hoist properties from constant object and array literals into regular variables subject to a set of constraints. For example: __INLINE_CODE_210__ is converted to __INLINE_CODE_211__. Note: __INLINE_CODE_212__ works best with __INLINE_CODE_213__ enabled, the __INLINE_CODE_214__ option __INLINE_CODE_215__ set to __INLINE_CODE_216__ or higher, and the __INLINE_CODE_217__ option __INLINE_CODE_218__ enabled.
__INLINE_CODE_219__ (default: __INLINE_CODE_220__) -- hoist __INLINE_CODE_221__ declarations (this is __INLINE_CODE_222__ by default because it seems to increase the size of the output in general)
__INLINE_CODE_223__ (default: __INLINE_CODE_224__) -- optimizations for if/return and if/continue
__INLINE_CODE_225__ (default: __INLINE_CODE_226__) -- inline calls to function with simple/__INLINE_CODE_227__ statement:
- __INLINE_CODE_228__ -- same as __INLINE_CODE_229__
- __INLINE_CODE_230__ -- disabled inlining
- __INLINE_CODE_231__ -- inline simple functions
- __INLINE_CODE_232__ -- inline functions with arguments
- __INLINE_CODE_233__ -- inline functions with arguments and variables
- __INLINE_CODE_234__ -- same as __INLINE_CODE_235__
__INLINE_CODE_236__ (default: __INLINE_CODE_237__) -- join consecutive __INLINE_CODE_238__ statements
__INLINE_CODE_239__ (default: __INLINE_CODE_240__) -- Pass __INLINE_CODE_241__ to prevent the compressor from discarding class names. See also: the __INLINE_CODE_242__ mangle option.
__INLINE_CODE_243__ (default: __INLINE_CODE_244__) -- Prevents the compressor from discarding unused function arguments. You need this for code which relies on __INLINE_CODE_245__.
__INLINE_CODE_246__ (default: __INLINE_CODE_247__) -- Pass __INLINE_CODE_248__ to prevent the compressor from discarding function names. Useful for code relying on __INLINE_CODE_249__. See also: the __INLINE_CODE_250__ mangle option.
__INLINE_CODE_251__ (default: __INLINE_CODE_252__) -- Pass __INLINE_CODE_253__ to prevent __INLINE_CODE_254__ from being compressed into __INLINE_CODE_255__, which may cause performance issues on Chrome.
__INLINE_CODE_256__ (default: __INLINE_CODE_257__) -- optimizations for __INLINE_CODE_258__, __INLINE_CODE_259__ and __INLINE_CODE_260__ loops when we can statically determine the condition.
__INLINE_CODE_261__ (default: __INLINE_CODE_262__) -- negate "Immediately-Called Function Expressions" where the return value is discarded, to avoid the parens that the code generator would insert.
__INLINE_CODE_263__ (default: __INLINE_CODE_264__) -- The maximum number of times to run compress. In some cases more than one pass leads to further compressed code. Keep in mind more passes will take more time.
__INLINE_CODE_265__ (default: __INLINE_CODE_266__) -- rewrite property access using the dot notation, for example __INLINE_CODE_267__
__INLINE_CODE_268__ (default: __INLINE_CODE_269__) -- 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 __INLINE_CODE_270__. If variable __INLINE_CODE_271__ is not used elsewhere, UglifyJS will drop it, but will still keep the __INLINE_CODE_272__, not knowing what it does. You can pass __INLINE_CODE_273__ 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).
__INLINE_CODE_274__ (default: __INLINE_CODE_275__) -- If you pass __INLINE_CODE_276__ for this, UglifyJS will assume that object property access (e.g. __INLINE_CODE_277__ or __INLINE_CODE_278__) doesn't have any side effects. Specify __INLINE_CODE_279__ to treat __INLINE_CODE_280__ as side-effect-free only when __INLINE_CODE_281__ is certain to not throw, i.e. not __INLINE_CODE_282__ or __INLINE_CODE_283__.
__INLINE_CODE_284__ (default: __INLINE_CODE_285__) -- Allows single-use functions to be inlined as function expressions when permissible allowing further optimization. Enabled by default. Option depends on __INLINE_CODE_286__ being enabled. Some code runs faster in the Chrome V8 engine if this option is disabled. Does not negatively impact other major browsers.
__INLINE_CODE_287__ (default: __INLINE_CODE_288__) -- Improve optimization on variables assigned with and used as constant values.
__INLINE_CODE_289__ (default: __INLINE_CODE_290__) -- 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 __INLINE_CODE_291__ then the default __INLINE_CODE_292__ limit is __INLINE_CODE_293__. Set option to __INLINE_CODE_294__ or __INLINE_CODE_295__ to disable. The smallest __INLINE_CODE_296__ length is __INLINE_CODE_297__. A __INLINE_CODE_298__ value of __INLINE_CODE_299__ is grandfathered to be equivalent to __INLINE_CODE_300__ and as such means __INLINE_CODE_301__. On rare occasions the default sequences limit leads to very slow compress times in which case a value of __INLINE_CODE_302__ or less is recommended.
__INLINE_CODE_303__ (default: __INLINE_CODE_304__) -- Pass __INLINE_CODE_305__ to disable potentially dropping functions marked as "pure". A function call is marked as "pure" if a comment annotation __INLINE_CODE_306__ or __INLINE_CODE_307__ immediately precedes the call. For example: __INLINE_CODE_308__
__INLINE_CODE_309__ (default: __INLINE_CODE_310__) -- de-duplicate and remove unreachable __INLINE_CODE_311__ branches
__INLINE_CODE_312__ (default: __INLINE_CODE_313__) -- drop unreferenced functions (__INLINE_CODE_314__) and/or variables (__INLINE_CODE_315__) in the top level scope (__INLINE_CODE_316__ by default, __INLINE_CODE_317__ to drop both unreferenced functions and variables)
__INLINE_CODE_318__ (default: __INLINE_CODE_319__) -- prevent specific toplevel functions and variables from __INLINE_CODE_320__ removal (can be array, comma-separated, RegExp or function. Implies __INLINE_CODE_321__)
__INLINE_CODE_322__ (default: __INLINE_CODE_323__) -- Transforms __INLINE_CODE_324__ into __INLINE_CODE_325__. Note: recommend to set this value to __INLINE_CODE_326__ for IE10 and earlier versions due to known issues.
__INLINE_CODE_327__ (default: __INLINE_CODE_328__) -- apply "unsafe" transformations (discussion below)
__INLINE_CODE_329__ (default: __INLINE_CODE_330__) -- Convert ES5 style anonymous function expressions to arrow functions if the function body does not reference __INLINE_CODE_331__. Note: it is not always safe to perform this conversion if code relies on the the function having a __INLINE_CODE_332__, which arrow functions lack. This transform requires that the __INLINE_CODE_333__ compress option is set to __INLINE_CODE_334__ or greater.
__INLINE_CODE_335__ (default: __INLINE_CODE_336__) -- Reverse __INLINE_CODE_337__ and __INLINE_CODE_338__ to __INLINE_CODE_339__ and __INLINE_CODE_340__ 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 __INLINE_CODE_341__, or __INLINE_CODE_342__. This could cause change in execution order after operands in the comparison are switching. Compression only works if both __INLINE_CODE_343__ and __INLINE_CODE_344__ are both set to true.
__INLINE_CODE_345__ (default: __INLINE_CODE_346__) -- compress and mangle __INLINE_CODE_347__ when both __INLINE_CODE_348__ and __INLINE_CODE_349__ are string literals.
__INLINE_CODE_350__ (default: __INLINE_CODE_351__) -- optimize numerical expressions like __INLINE_CODE_352__ into __INLINE_CODE_353__, which may give imprecise floating point results.
__INLINE_CODE_354__ (default: false) -- Converts __INLINE_CODE_355__ to __INLINE_CODE_356__. __INLINE_CODE_357__ must be set to __INLINE_CODE_358__ or greater to enable this transform. If __INLINE_CODE_359__ is a RegExp then key/value pairs with keys matching the RegExp will be converted to concise methods. Note: if enabled there is a risk of getting a "__INLINE_CODE_360__ is not a constructor" TypeError should any code try to __INLINE_CODE_361__ the former function.
__INLINE_CODE_362__ (default: __INLINE_CODE_363__) -- optimize expressions like __INLINE_CODE_364__ into __INLINE_CODE_365__
__INLINE_CODE_366__ (default: __INLINE_CODE_367__) -- enable substitutions of variables with __INLINE_CODE_368__ values the same way as if they are constants.
__INLINE_CODE_369__ (default: __INLINE_CODE_370__) -- substitute __INLINE_CODE_371__ if there is a variable named __INLINE_CODE_372__ in scope (variable name will be mangled, typically reduced to a single character)
__INLINE_CODE_373__ (default: __INLINE_CODE_374__) -- drop unreferenced functions and variables (simple direct variable assignments do not count as references unless set to __INLINE_CODE_375__)
__INLINE_CODE_376__ (default: __INLINE_CODE_377__) -- display warnings when dropping unreachable code or unused declarations etc.

Mangle options

__INLINE_CODE_378__ (default __INLINE_CODE_379__) -- Pass __INLINE_CODE_380__ to mangle names visible in scopes where __INLINE_CODE_381__ or __INLINE_CODE_382__ are used.
__INLINE_CODE_383__ (default __INLINE_CODE_384__) -- Pass __INLINE_CODE_385__ to not mangle class names. See also: the __INLINE_CODE_386__ compress option.
__INLINE_CODE_387__ (default __INLINE_CODE_388__) -- Pass __INLINE_CODE_389__ to not mangle function names. Useful for code relying on __INLINE_CODE_390__. See also: the __INLINE_CODE_391__ compress option.
__INLINE_CODE_392__ (default __INLINE_CODE_393__) -- Pass an array of identifiers that should be excluded from mangling. Example: __INLINE_CODE_394__.
__INLINE_CODE_395__ (default __INLINE_CODE_396__) -- Pass __INLINE_CODE_397__ to mangle names declared in the top level scope.
__INLINE_CODE_398__ (default __INLINE_CODE_399__) -- Pass __INLINE_CODE_400__ to work around the Safari 10 loop iterator bug "Cannot declare a let variable twice". See also: the __INLINE_CODE_401__ output option.

Examples:

__CODE_BLOCK_37__ __CODE_BLOCK_38__

Mangle properties options

__INLINE_CODE_402__ (default: __INLINE_CODE_403__) -- Use __INLINE_CODE_404__ to allow the mangling of builtin DOM properties. Not recommended to override this setting.
__INLINE_CODE_405__ (default: __INLINE_CODE_406__) -— Mangle names with the original name still present. Pass an empty string __INLINE_CODE_407__ to enable, or a non-empty string to set the debug suffix.
__INLINE_CODE_408__ (default: __INLINE_CODE_409__) -— Only mangle unquoted property names.
__INLINE_CODE_410__ (default: __INLINE_CODE_411__) -— Pass a RegExp literal to only mangle property names matching the regular expression.
__INLINE_CODE_412__ (default: __INLINE_CODE_413__) -- Do not mangle property names listed in the __INLINE_CODE_414__ array.

Output options

The code generator tries to output shortest code possible by default. In case you want beautified output, pass __INLINE_CODE_415__ (__INLINE_CODE_416__). Optionally you can pass additional arguments that control the code output:

__INLINE_CODE_417__ (default __INLINE_CODE_418__) -- escape Unicode characters in strings and regexps (affects directives with non-ascii characters becoming invalid)
__INLINE_CODE_419__ (default __INLINE_CODE_420__) -- whether to actually beautify the output. Passing __INLINE_CODE_421__ will set this to true, but you might need to pass __INLINE_CODE_422__ even when you want to generate minified code, in order to specify additional arguments, so you can use __INLINE_CODE_423__ to override it.
__INLINE_CODE_424__ (default __INLINE_CODE_425__) -- always insert brackets in __INLINE_CODE_426__, __INLINE_CODE_427__, __INLINE_CODE_428__, __INLINE_CODE_429__ or __INLINE_CODE_430__ statements, even if their body is a single statement.
__INLINE_CODE_431__ (default __INLINE_CODE_432__) -- pass __INLINE_CODE_433__ or __INLINE_CODE_434__ to preserve all comments, __INLINE_CODE_435__ to preserve some comments, a regular expression string (e.g. __INLINE_CODE_436__) or a function.
__INLINE_CODE_437__ (default __INLINE_CODE_438__) -- set output printing mode. Set __INLINE_CODE_439__ to __INLINE_CODE_440__ or greater to emit shorthand object properties - i.e.: __INLINE_CODE_441__ instead of __INLINE_CODE_442__. The __INLINE_CODE_443__ option will only change the output in direct control of the beautifier. Non-compatible features in the abstract syntax tree will still be output as is. For example: an __INLINE_CODE_444__ setting of __INLINE_CODE_445__ will not convert ES6+ code to ES5.
__INLINE_CODE_446__ (default __INLINE_CODE_447__)
__INLINE_CODE_448__ (default __INLINE_CODE_449__) -- prefix all lines by that many spaces
__INLINE_CODE_450__ (default __INLINE_CODE_451__) -- escape the slash in occurrences of __INLINE_CODE_452__ in strings
__INLINE_CODE_453__ (default __INLINE_CODE_454__) -- when turned on, prevents stripping quotes from property names in object literals.
__INLINE_CODE_455__ (default __INLINE_CODE_456__) -- maximum line length (for uglified code)
__INLINE_CODE_457__ (default __INLINE_CODE_458__) -- 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.
__INLINE_CODE_459__ (default __INLINE_CODE_460__) -- pass __INLINE_CODE_461__ to preserve lines, but it only works if __INLINE_CODE_462__ is set to __INLINE_CODE_463__.
__INLINE_CODE_464__ (default __INLINE_CODE_465__) -- pass __INLINE_CODE_466__ to quote all keys in literal objects
__INLINE_CODE_467__ (default __INLINE_CODE_468__) -- preferred quote style for strings (affects quoted property names and directives as well):
- __INLINE_CODE_469__ -- prefers double quotes, switches to single quotes when there are more double quotes in the string itself. __INLINE_CODE_470__ is best for gzip size.
- __INLINE_CODE_471__ -- always use single quotes
- __INLINE_CODE_472__ -- always use double quotes
- __INLINE_CODE_473__ -- always use the original quotes
__INLINE_CODE_474__ (default __INLINE_CODE_475__) -- set this option to __INLINE_CODE_476__ to work around the Safari 10/11 await bug. See also: the __INLINE_CODE_477__ mangle option.
__INLINE_CODE_478__ (default __INLINE_CODE_479__) -- separate statements with semicolons. If you pass __INLINE_CODE_480__ 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).
__INLINE_CODE_481__ (default __INLINE_CODE_482__) -- preserve shebang __INLINE_CODE_483__ in preamble (bash scripts)
__INLINE_CODE_484__ (default __INLINE_CODE_485__) -- enable workarounds for WebKit bugs. PhantomJS users should set this option to __INLINE_CODE_486__.
__INLINE_CODE_487__ (default __INLINE_CODE_488__) -- 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.
__INLINE_CODE_489__ (default __INLINE_CODE_490__) -- pass __INLINE_CODE_491__ to wrap immediately invoked function expressions. See #640 for more details.

Miscellaneous

Keeping copyright notices or other comments

You can pass __INLINE_CODE_492__ 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 __INLINE_CODE_493__ to keep all the comments, or a valid JavaScript regexp to keep only comments that match this regexp. For example __INLINE_CODE_494__ will keep comments like __INLINE_CODE_495__.

Note, however, that there might be situations where comments are lost. For example:

__CODE_BLOCK_39__

Even though it has "@preserve", the comment will be lost because the inner function __INLINE_CODE_496__ (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.

The __INLINE_CODE_497 INLINE_CODE_498__ option

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:

__INLINE_CODE_499__ or __INLINE_CODE_500__ → __INLINE_CODE_501__
__INLINE_CODE_502__ → __INLINE_CODE_503__
__INLINE_CODE_504__ or __INLINE_CODE_505__ → __INLINE_CODE_506__
__INLINE_CODE_507__ → we discard the __INLINE_CODE_508__

Conditional compilation

You can use the __INLINE_CODE_509__ (__INLINE_CODE_510__) switch in order to declare global variables that UglifyJS will assume to be constants (unless defined in scope). For example if you pass __INLINE_CODE_511__ then, coupled with dead code removal UglifyJS will discard the following from the output:

__CODE_BLOCK_40__

You can specify nested constants in the form of __INLINE_CODE_512__.

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 __INLINE_CODE_513__ 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 __INLINE_CODE_514__ file with the following:

__CODE_BLOCK_41__

and build your code like this:

__CODE_BLOCK_42__

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 __INLINE_CODE_515__ declarations if you use them. If you are targeting < ES6 environments which does not support __INLINE_CODE_516__, using __INLINE_CODE_517__ with __INLINE_CODE_518__ (enabled by default) should suffice.

Conditional compilation API

You can also use conditional compilation via the programmatic API. With the difference that the property name is __INLINE_CODE_519__ and is a compressor property:

__CODE_BLOCK_43__

To replace an identifier with an arbitrary non-constant expression it is necessary to prefix the __INLINE_CODE_520__ key with __INLINE_CODE_521__ to instruct UglifyJS to parse the value as an expression:

__CODE_BLOCK_44__

Otherwise it would be replaced as string literal:

__CODE_BLOCK_45__

Using native Uglify AST with __INLINE_CODE_522__

__CODE_BLOCK_46__ __CODE_BLOCK_47__

Working with Uglify AST

Transversal and transformation of the native AST can be performed through __INLINE_CODE_523__ and __INLINE_CODE_524__ respectively.

ESTree / SpiderMonkey AST

UglifyJS 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:

__CODE_BLOCK_48__

The __INLINE_CODE_525__ 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 __INLINE_CODE_526__ option which will use Acorn to do all the parsing. If you pass this option, UglifyJS will __INLINE_CODE_527__.

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.

Uglify Fast Minify Mode

It's not well known, but whitespace removal and symbol mangling accounts for 95% of the size reduction in minified code for most JavaScript - not elaborate code transforms. One can simply disable __INLINE_CODE_528__ to speed up Uglify builds by 3 to 4 times. In this fast __INLINE_CODE_529__-only mode Uglify has comparable minify speeds and gzip sizes to __INLINE_CODE_530__:

d3.js	minify size	gzip size	minify time (seconds)
original	451,131	108,733	-
uglify-js@3.0.24 mangle=false, compress=false	316,600	85,245	0.70
uglify-js@3.0.24 mangle=true, compress=false	220,216	72,730	1.13
butternut@0.4.6	217,568	72,738	1.41
uglify-js@3.0.24 mangle=true, compress=true	212,511	71,560	3.36
babili@0.1.4	210,713	72,140	12.64

To enable fast minify mode from the CLI use:

__CODE_BLOCK_49__

To enable fast minify mode with the API use:

__CODE_BLOCK_50__

Keywords

uglify uglify-es uglify-js minify minifier javascript ecmascript es5 es6 es7 es8 es2015 es2016 es2017 async await