UglifyJS 3
UglifyJS is a JavaScript parser, minifier, compressor and beautifier toolkit.
Note:
uglify-js@3has a simplified API and CLI that is not backwards compatible withuglify-js@2.- Documentation for UglifyJS
2.xreleases can be found here. uglify-jsonly supports JavaScript (ECMAScript 5).- To minify ECMAScript 2015 or above, transpile using tools like Babel.
Install
First make sure you have installed the latest version of node.js (You may need to restart your computer after this step).
From NPM for use as a command line app:
npm install uglify-js -gFrom NPM for programmatic use:
npm install uglify-jsCommand line usage
uglifyjs [input files] [options]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.jsCommand 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.
--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-fnames Do not mangle/drop function names. Useful for
code relying on Function.prototype.name.
--name-cache <file> File to hold mangled name mappings.
--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 HTTPX-SourceMapis 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=falseCLI mangle options
To enable the mangler you need to pass --mangle (-m). The following
(comma-separated) options are supported:
toplevel(defaultfalse) -- mangle names declared in the top level scope.eval(defaultfalse) -- mangle names visible in scopes whereevalorwithare used.
When mangling is enabled but you want to prevent certain names from being
mangled, you can declare those names with --mangle reserved — pass a
comma-separated list of names. For example:
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-js");
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
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_fnames (default: false) - pass true to prevent discarding or mangling
of function names. Useful for code relying on Function.prototype.name.
Minify options structure
{
parse: {
// parse options
},
compress: {
// compress options
},
mangle: {
// mangle options
properties: {
// mangle property options
}
},
output: {
// output options
},
sourceMap: {
// source map options
},
nameCache: null, // or specify a name cache object
toplevel: false,
ie8: 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
html5_comments (default true)
shebang (default true) -- support #!command as the first line
Compress options
arguments (default: true) -- replace arguments[index] with function
parameter name whenever possible.
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, attempts to negate binary nodes, e.g.
a = !b && !c && !d && !e → a=!(b||c||d||e) etc.
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
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 00 -- disabled inlining1 -- inline simple functions2 -- inline functions with arguments3 -- inline functions with arguments and variablestrue -- same as 3
join_vars (default: true) -- join consecutive var statements
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). Make sure symbols under pure_funcs
are also under mangle.reserved to avoid mangling.
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_comps (default: false) -- compress expressions like a <= b assuming
none of the operands can be (coerced to) NaN.
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_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_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.
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.
braces (default false) -- always insert braces 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.
indent_level (default 4)
indent_start (default 0) -- prefix all lines by that many spaces
inline_script (default true) -- escape HTML comments and 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 quotes2 -- always use double quotes3 -- always use the original quotes
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() → "" + expnew 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 });
Source maps and debugging
Various compress transforms that simplify, rearrange, inline and remove code
are known to have an adverse effect on debugging with source maps. This is
expected as code is optimized and mappings are often simply not possible as
some code no longer exists. For highest fidelity in source map debugging
disable the Uglify compress option and just use mangle.
Compiler assumptions
To allow for better optimizations, the compiler makes various assumptions:
.toString() and .valueOf() don't have side effects, and for built-in
objects they have not been overridden.undefined, NaN and Infinity have not been externally redefined.arguments.callee, arguments.caller and Function.prototype.caller are not used.- The code doesn't expect the contents of
Function.prototype.toString() or
Error.prototype.stack to be anything in particular.
- Getting and setting properties on a plain object does not cause other side effects
(using
.watch() or Proxy).
- Object properties can be added, removed and modified (not prevented with
Object.defineProperty(), Object.defineProperties(), Object.freeze(),
Object.preventExtensions() or Object.seal()).
,'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__ to return compressor warnings in __INLINE_CODE_77__. Use the value __INLINE_CODE_78__ for more detailed warnings.
__INLINE_CODE_79__ (default __INLINE_CODE_80__) — pass an object if you wish to specify some additional parse options.
__INLINE_CODE_81__ (default __INLINE_CODE_82__) — pass __INLINE_CODE_83__ to skip compressing entirely. Pass an object to specify custom compress options.
__INLINE_CODE_84__ (default __INLINE_CODE_85__) — pass __INLINE_CODE_86__ to skip mangling names, or pass an object to specify mangle options (see below).
- __INLINE_CODE_87__ (default __INLINE_CODE_88__) — a subcategory of the mangle option. Pass an object to specify custom mangle property options.
__INLINE_CODE_89__ (default __INLINE_CODE_90__) — pass an object if you wish to specify additional output options. The defaults are optimized for best compression.
__INLINE_CODE_91__ (default __INLINE_CODE_92__) - pass an object if you wish to specify source map options.
__INLINE_CODE_93__ (default __INLINE_CODE_94__) - set to __INLINE_CODE_95__ if you wish to enable top level variable and function name mangling and to drop unused variables and functions.
__INLINE_CODE_96__ (default __INLINE_CODE_97__) - pass an empty object __INLINE_CODE_98__ or a previously used __INLINE_CODE_99__ object if you wish to cache mangled variable and property names across multiple invocations of __INLINE_CODE_100__. Note: this is a read/write property. __INLINE_CODE_101__ 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_102__ (default __INLINE_CODE_103__) - set to __INLINE_CODE_104__ to support IE8.
__INLINE_CODE_105__ (default: __INLINE_CODE_106__) - pass __INLINE_CODE_107__ to prevent discarding or mangling of function names. Useful for code relying on __INLINE_CODE_108__.
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_109__. The value passed for __INLINE_CODE_110__ is only used to set __INLINE_CODE_111__ in __INLINE_CODE_112__. The value of __INLINE_CODE_113__ is only used to set __INLINE_CODE_114__ attribute (see the spec) in source map file.
You can set option __INLINE_CODE_115__ to be __INLINE_CODE_116__ 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_117__:
__CODE_BLOCK_36__If you're using the __INLINE_CODE_118__ header instead, you can just omit __INLINE_CODE_119__.
Parse options
__INLINE_CODE_120__ (default __INLINE_CODE_121__) -- support top level __INLINE_CODE_122__ statements
__INLINE_CODE_123__ (default __INLINE_CODE_124__)
__INLINE_CODE_125__ (default __INLINE_CODE_126__) -- support __INLINE_CODE_127__ as the first line
Compress options
__INLINE_CODE_128__ (default: __INLINE_CODE_129__) -- replace __INLINE_CODE_130__ with function parameter name whenever possible.
__INLINE_CODE_131__ (default: __INLINE_CODE_132__) -- various optimizations for boolean context, for example __INLINE_CODE_133__
__INLINE_CODE_134__ (default: __INLINE_CODE_135__) -- Collapse single-use non-constant variables, side effects permitting.
__INLINE_CODE_136__ (default: __INLINE_CODE_137__) -- apply certain optimizations to binary nodes, e.g. __INLINE_CODE_138__, attempts to negate binary nodes, e.g. __INLINE_CODE_139__ etc.
__INLINE_CODE_140__ (default: __INLINE_CODE_141__) -- apply optimizations for __INLINE_CODE_142__-s and conditional expressions
__INLINE_CODE_143__ (default: __INLINE_CODE_144__) -- remove unreachable code
__INLINE_CODE_145__ (default: __INLINE_CODE_146__) -- Pass __INLINE_CODE_147__ to discard calls to __INLINE_CODE_148__ functions. If you wish to drop a specific function call such as __INLINE_CODE_149__ and/or retain side effects from function arguments after dropping the function call then use __INLINE_CODE_150__ instead.
__INLINE_CODE_151__ (default: __INLINE_CODE_152__) -- remove __INLINE_CODE_153__ statements
__INLINE_CODE_154__ (default: __INLINE_CODE_155__) -- attempt to evaluate constant expressions
__INLINE_CODE_156__ (default: __INLINE_CODE_157__) -- Pass __INLINE_CODE_158__ to preserve completion values from terminal statements without __INLINE_CODE_159__, e.g. in bookmarklets.
__INLINE_CODE_160__ (default: __INLINE_CODE_161__) -- see conditional compilation
__INLINE_CODE_162__ (default: __INLINE_CODE_163__) -- hoist function declarations
__INLINE_CODE_164__ (default: __INLINE_CODE_165__) -- hoist properties from constant object and array literals into regular variables subject to a set of constraints. For example: __INLINE_CODE_166__ is converted to __INLINE_CODE_167__. Note: __INLINE_CODE_168__ works best with __INLINE_CODE_169__ enabled, the __INLINE_CODE_170__ option __INLINE_CODE_171__ set to __INLINE_CODE_172__ or higher, and the __INLINE_CODE_173__ option __INLINE_CODE_174__ enabled.
__INLINE_CODE_175__ (default: __INLINE_CODE_176__) -- hoist __INLINE_CODE_177__ declarations (this is __INLINE_CODE_178__ by default because it seems to increase the size of the output in general)
__INLINE_CODE_179__ (default: __INLINE_CODE_180__) -- optimizations for if/return and if/continue
__INLINE_CODE_181__ (default: __INLINE_CODE_182__) -- inline calls to function with simple/__INLINE_CODE_183__ statement:
- __INLINE_CODE_184__ -- same as __INLINE_CODE_185__
- __INLINE_CODE_186__ -- disabled inlining
- __INLINE_CODE_187__ -- inline simple functions
- __INLINE_CODE_188__ -- inline functions with arguments
- __INLINE_CODE_189__ -- inline functions with arguments and variables
- __INLINE_CODE_190__ -- same as __INLINE_CODE_191__
__INLINE_CODE_192__ (default: __INLINE_CODE_193__) -- join consecutive __INLINE_CODE_194__ statements
__INLINE_CODE_195__ (default: __INLINE_CODE_196__) -- Prevents the compressor from discarding unused function arguments. You need this for code which relies on __INLINE_CODE_197__.
__INLINE_CODE_198__ (default: __INLINE_CODE_199__) -- Pass __INLINE_CODE_200__ to prevent the compressor from discarding function names. Useful for code relying on __INLINE_CODE_201__. See also: the __INLINE_CODE_202__ mangle option.
__INLINE_CODE_203__ (default: __INLINE_CODE_204__) -- Pass __INLINE_CODE_205__ to prevent __INLINE_CODE_206__ from being compressed into __INLINE_CODE_207__, which may cause performance issues on Chrome.
__INLINE_CODE_208__ (default: __INLINE_CODE_209__) -- optimizations for __INLINE_CODE_210__, __INLINE_CODE_211__ and __INLINE_CODE_212__ loops when we can statically determine the condition.
__INLINE_CODE_213__ (default: __INLINE_CODE_214__) -- negate "Immediately-Called Function Expressions" where the return value is discarded, to avoid the parens that the code generator would insert.
__INLINE_CODE_215__ (default: __INLINE_CODE_216__) -- 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_217__ (default: __INLINE_CODE_218__) -- rewrite property access using the dot notation, for example __INLINE_CODE_219__
__INLINE_CODE_220__ (default: __INLINE_CODE_221__) -- 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_222__. If variable __INLINE_CODE_223__ is not used elsewhere, UglifyJS will drop it, but will still keep the __INLINE_CODE_224__, not knowing what it does. You can pass __INLINE_CODE_225__ 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). Make sure symbols under __INLINE_CODE_226__ are also under __INLINE_CODE_227__ to avoid mangling.
__INLINE_CODE_228__ (default: __INLINE_CODE_229__) -- If you pass __INLINE_CODE_230__ for this, UglifyJS will assume that object property access (e.g. __INLINE_CODE_231__ or __INLINE_CODE_232__) doesn't have any side effects. Specify __INLINE_CODE_233__ to treat __INLINE_CODE_234__ as side-effect-free only when __INLINE_CODE_235__ is certain to not throw, i.e. not __INLINE_CODE_236__ or __INLINE_CODE_237__.
__INLINE_CODE_238__ (default: __INLINE_CODE_239__) -- Allows single-use functions to be inlined as function expressions when permissible allowing further optimization. Enabled by default. Option depends on __INLINE_CODE_240__ 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_241__ (default: __INLINE_CODE_242__) -- Improve optimization on variables assigned with and used as constant values.
__INLINE_CODE_243__ (default: __INLINE_CODE_244__) -- 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_245__ then the default __INLINE_CODE_246__ limit is __INLINE_CODE_247__. Set option to __INLINE_CODE_248__ or __INLINE_CODE_249__ to disable. The smallest __INLINE_CODE_250__ length is __INLINE_CODE_251__. A __INLINE_CODE_252__ value of __INLINE_CODE_253__ is grandfathered to be equivalent to __INLINE_CODE_254__ and as such means __INLINE_CODE_255__. On rare occasions the default sequences limit leads to very slow compress times in which case a value of __INLINE_CODE_256__ or less is recommended.
__INLINE_CODE_257__ (default: __INLINE_CODE_258__) -- Pass __INLINE_CODE_259__ to disable potentially dropping functions marked as "pure". A function call is marked as "pure" if a comment annotation __INLINE_CODE_260__ or __INLINE_CODE_261__ immediately precedes the call. For example: __INLINE_CODE_262__
__INLINE_CODE_263__ (default: __INLINE_CODE_264__) -- de-duplicate and remove unreachable __INLINE_CODE_265__ branches
__INLINE_CODE_266__ (default: __INLINE_CODE_267__) -- drop unreferenced functions (__INLINE_CODE_268__) and/or variables (__INLINE_CODE_269__) in the top level scope (__INLINE_CODE_270__ by default, __INLINE_CODE_271__ to drop both unreferenced functions and variables)
__INLINE_CODE_272__ (default: __INLINE_CODE_273__) -- prevent specific toplevel functions and variables from __INLINE_CODE_274__ removal (can be array, comma-separated, RegExp or function. Implies __INLINE_CODE_275__)
__INLINE_CODE_276__ (default: __INLINE_CODE_277__) -- Transforms __INLINE_CODE_278__ into __INLINE_CODE_279__. Note: recommend to set this value to __INLINE_CODE_280__ for IE10 and earlier versions due to known issues.
__INLINE_CODE_281__ (default: __INLINE_CODE_282__) -- apply "unsafe" transformations (discussion below)
__INLINE_CODE_283__ (default: __INLINE_CODE_284__) -- compress expressions like __INLINE_CODE_285__ assuming none of the operands can be (coerced to) __INLINE_CODE_286__.
__INLINE_CODE_287__ (default: __INLINE_CODE_288__) -- compress and mangle __INLINE_CODE_289__ when both __INLINE_CODE_290__ and __INLINE_CODE_291__ are string literals.
__INLINE_CODE_292__ (default: __INLINE_CODE_293__) -- optimize numerical expressions like __INLINE_CODE_294__ into __INLINE_CODE_295__, which may give imprecise floating point results.
__INLINE_CODE_296__ (default: __INLINE_CODE_297__) -- optimize expressions like __INLINE_CODE_298__ into __INLINE_CODE_299__
__INLINE_CODE_300__ (default: __INLINE_CODE_301__) -- enable substitutions of variables with __INLINE_CODE_302__ values the same way as if they are constants.
__INLINE_CODE_303__ (default: __INLINE_CODE_304__) -- substitute __INLINE_CODE_305__ if there is a variable named __INLINE_CODE_306__ in scope (variable name will be mangled, typically reduced to a single character)
__INLINE_CODE_307__ (default: __INLINE_CODE_308__) -- drop unreferenced functions and variables (simple direct variable assignments do not count as references unless set to __INLINE_CODE_309__)
__INLINE_CODE_310__ (default: __INLINE_CODE_311__) -- display warnings when dropping unreachable code or unused declarations etc.
Mangle options
__INLINE_CODE_312__ (default __INLINE_CODE_313__) -- Pass __INLINE_CODE_314__ to mangle names visible in scopes where __INLINE_CODE_315__ or __INLINE_CODE_316__ are used.
__INLINE_CODE_317__ (default __INLINE_CODE_318__) -- Pass __INLINE_CODE_319__ to not mangle function names. Useful for code relying on __INLINE_CODE_320__. See also: the __INLINE_CODE_321__ compress option.
__INLINE_CODE_322__ (default __INLINE_CODE_323__) -- Pass an array of identifiers that should be excluded from mangling. Example: __INLINE_CODE_324__.
__INLINE_CODE_325__ (default __INLINE_CODE_326__) -- Pass __INLINE_CODE_327__ to mangle names declared in the top level scope.
Examples:
__CODE_BLOCK_37__ __CODE_BLOCK_38__Mangle properties options
__INLINE_CODE_328__ (default: __INLINE_CODE_329__) -- Use __INLINE_CODE_330__ to allow the mangling of builtin DOM properties. Not recommended to override this setting.
__INLINE_CODE_331__ (default: __INLINE_CODE_332__) -— Mangle names with the original name still present. Pass an empty string __INLINE_CODE_333__ to enable, or a non-empty string to set the debug suffix.
__INLINE_CODE_334__ (default: __INLINE_CODE_335__) -— Only mangle unquoted property names.
__INLINE_CODE_336__ (default: __INLINE_CODE_337__) -— Pass a RegExp literal to only mangle property names matching the regular expression.
__INLINE_CODE_338__ (default: __INLINE_CODE_339__) -- Do not mangle property names listed in the __INLINE_CODE_340__ array.
Output options
The code generator tries to output shortest code possible by default. In case you want beautified output, pass __INLINE_CODE_341__ (__INLINE_CODE_342__). Optionally you can pass additional arguments that control the code output:
__INLINE_CODE_343__ (default __INLINE_CODE_344__) -- escape Unicode characters in strings and regexps (affects directives with non-ascii characters becoming invalid)
__INLINE_CODE_345__ (default __INLINE_CODE_346__) -- whether to actually beautify the output. Passing __INLINE_CODE_347__ will set this to true, but you might need to pass __INLINE_CODE_348__ even when you want to generate minified code, in order to specify additional arguments, so you can use __INLINE_CODE_349__ to override it.
__INLINE_CODE_350__ (default __INLINE_CODE_351__) -- always insert braces in __INLINE_CODE_352__, __INLINE_CODE_353__, __INLINE_CODE_354__, __INLINE_CODE_355__ or __INLINE_CODE_356__ statements, even if their body is a single statement.
__INLINE_CODE_357__ (default __INLINE_CODE_358__) -- pass __INLINE_CODE_359__ or __INLINE_CODE_360__ to preserve all comments, __INLINE_CODE_361__ to preserve some comments, a regular expression string (e.g. __INLINE_CODE_362__) or a function.
__INLINE_CODE_363__ (default __INLINE_CODE_364__)
__INLINE_CODE_365__ (default __INLINE_CODE_366__) -- prefix all lines by that many spaces
__INLINE_CODE_367__ (default __INLINE_CODE_368__) -- escape HTML comments and the slash in occurrences of __INLINE_CODE_369__ in strings
__INLINE_CODE_370__ (default __INLINE_CODE_371__) -- when turned on, prevents stripping quotes from property names in object literals.
__INLINE_CODE_372__ (default __INLINE_CODE_373__) -- maximum line length (for uglified code)
__INLINE_CODE_374__ (default __INLINE_CODE_375__) -- 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_376__ (default __INLINE_CODE_377__) -- pass __INLINE_CODE_378__ to preserve lines, but it only works if __INLINE_CODE_379__ is set to __INLINE_CODE_380__.
__INLINE_CODE_381__ (default __INLINE_CODE_382__) -- pass __INLINE_CODE_383__ to quote all keys in literal objects
__INLINE_CODE_384__ (default __INLINE_CODE_385__) -- preferred quote style for strings (affects quoted property names and directives as well):
- __INLINE_CODE_386__ -- prefers double quotes, switches to single quotes when there are more double quotes in the string itself. __INLINE_CODE_387__ is best for gzip size.
- __INLINE_CODE_388__ -- always use single quotes
- __INLINE_CODE_389__ -- always use double quotes
- __INLINE_CODE_390__ -- always use the original quotes
__INLINE_CODE_391__ (default __INLINE_CODE_392__) -- separate statements with semicolons. If you pass __INLINE_CODE_393__ 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_394__ (default __INLINE_CODE_395__) -- preserve shebang __INLINE_CODE_396__ in preamble (bash scripts)
__INLINE_CODE_397__ (default __INLINE_CODE_398__) -- enable workarounds for WebKit bugs. PhantomJS users should set this option to __INLINE_CODE_399__.
__INLINE_CODE_400__ (default __INLINE_CODE_401__) -- 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_402__ (default __INLINE_CODE_403__) -- pass __INLINE_CODE_404__ to wrap immediately invoked function expressions. See #640 for more details.
Miscellaneous
Keeping copyright notices or other comments
You can pass __INLINE_CODE_405__ 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_406__ to keep all the comments, or a valid JavaScript regexp to keep only comments that match this regexp. For example __INLINE_CODE_407__ will keep comments like __INLINE_CODE_408__.
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_409__ (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_410__ __INLINE_CODE_411__ 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_412__ or __INLINE_CODE_413__ → __INLINE_CODE_414__
- __INLINE_CODE_415__ → __INLINE_CODE_416__
- __INLINE_CODE_417__ or __INLINE_CODE_418__ → __INLINE_CODE_419__
- __INLINE_CODE_420__ → we discard the __INLINE_CODE_421__
Conditional compilation
You can use the __INLINE_CODE_422__ (__INLINE_CODE_423__) 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_424__ 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_425__.
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_426__ 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_427__ 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_428__ declarations if you use them. If you are targeting < ES6 environments which does not support __INLINE_CODE_429__, using __INLINE_CODE_430__ with __INLINE_CODE_431__ (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_432__ 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_433__ key with __INLINE_CODE_434__ 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_435__
__CODE_BLOCK_46__ __CODE_BLOCK_47__Working with Uglify AST
Transversal and transformation of the native AST can be performed through __INLINE_CODE_436__ and __INLINE_CODE_437__ 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_438__ 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_439__ option which will use Acorn to do all the parsing. If you pass this option, UglifyJS will __INLINE_CODE_440__.
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_441__ to speed up Uglify builds by 3 to 4 times. In this fast __INLINE_CODE_442__-only mode Uglify has comparable minify speeds and gzip sizes to __INLINE_CODE_443__:
| 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__Source maps and debugging
Various __INLINE_CODE_444__ transforms that simplify, rearrange, inline and remove code are known to have an adverse effect on debugging with source maps. This is expected as code is optimized and mappings are often simply not possible as some code no longer exists. For highest fidelity in source map debugging disable the Uglify __INLINE_CODE_445__ option and just use __INLINE_CODE_446__.
Compiler assumptions
To allow for better optimizations, the compiler makes various assumptions:
- __INLINE_CODE_447__ and __INLINE_CODE_448__ don't have side effects, and for built-in objects they have not been overridden.
- __INLINE_CODE_449__, __INLINE_CODE_450__ and __INLINE_CODE_451__ have not been externally redefined.
- __INLINE_CODE_452__, __INLINE_CODE_453__ and __INLINE_CODE_454__ are not used.
- The code doesn't expect the contents of __INLINE_CODE_455__ or __INLINE_CODE_456__ to be anything in particular.
- Getting and setting properties on a plain object does not cause other side effects (using __INLINE_CODE_457__ or __INLINE_CODE_458__).
- Object properties can be added, removed and modified (not prevented with __INLINE_CODE_459__, __INLINE_CODE_460__, __INLINE_CODE_461__, __INLINE_CODE_462__ or __INLINE_CODE_463__).