A JavaScript mangler/compressor toolkit for ES6+.

note: You can support this project on patreon: [link] The Terser Patreon is shutting down in favor of opencollective. Check out PATRONS.md for our first-tier patrons.

Terser recommends you use RollupJS to bundle your modules, as that produces smaller code overall.

Beautification has been undocumented and is being removed from terser, we recommend you use prettier.

Find the changelog in CHANGELOG.md

Why choose terser?

uglify-es is no longer maintained and uglify-js does not support ES6+.

terser is a fork of uglify-es that mostly retains API and CLI compatibility with uglify-es and uglify-js@3.

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 terser -g

From NPM for programmatic use:

npm install terser

Command line usage

terser [input files] [options]

Terser can take multiple input files. It's recommended that you pass the input files first, then pass the options. Terser 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.

Command line arguments that take options (like --parse, --compress, --mangle and --format) can take in a comma-separated list of default option overrides. For instance:

terser input.js --compress ecma=2015,computed_props=false

If no input file is specified, Terser 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:

terser --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 and DOM
                                            API props.
                                `debug`  Add debug prefix and suffix.
                                `keep_quoted`  Only mangle unquoted properties, quoted
                                               properties are automatically reserved.
                                               `strict` disables quoted properties
                                               being automatically reserved.
                                `regex`  Only mangle matched property names.
                                `only_annotated` Only mangle properties defined with /*@__MANGLE_PROP__*/.
                                `reserved`  List of names that should not be mangled.
    -f, --format [options]      Specify format options.
                                `preamble`  Preamble to prepend to the output. You
                                            can use this to insert a comment, for
                                            example for licensing information.
                                            This will not be parsed, but the source
                                            map will adjust for its presence.
                                `quote_style`  Quote style:
                                               0 - auto
                                               1 - single
                                               2 - double
                                               3 - original
                                `wrap_iife`  Wrap IIFEs in parenthesis. Note: you may
                                             want to disable `negate_iife` under
                                             compressor options.
                                `wrap_func_args`  Wrap function arguments in parenthesis.
    -o, --output <file>         Output file path (default STDOUT). Specify `ast` or
                                `spidermonkey` to write Terser or SpiderMonkey AST
                                as JSON to STDOUT respectively.
    --comments [filter]         Preserve copyright comments in the output. By
                                default this works like Google Closure, keeping
                                JSDoc-style comments that contain e.g. "@license",
                                or start with "!". You can optionally pass one of the
                                following arguments to this flag:
                                - "all" to keep all comments
                                - `false` to omit comments in the output
                                - 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, 2015, 2016, etc.
    -e, --enclose [arg[:value]] Embed output in a big function with configurable
                                arguments and values.
    --ie8                       Support non-standard Internet Explorer 8.
                                Equivalent to setting `ie8: true` in `minify()`
                                for `compress`, `mangle` and `format` options.
                                By default Terser will not try to be IE-proof.
    --keep-classnames           Do not mangle/drop class names.
    --keep-fnames               Do not mangle/drop function names.  Useful for
                                code relying on Function.prototype.name.
    --module                    Input is an ES6 module. If `compress` or `mangle` is
                                enabled then the `toplevel` option, as well as strict mode,
                                will be enabled.
    --name-cache <file>         File to hold mangled name mappings.
    --safari10                  Support non-standard Safari 10/11.
                                Equivalent to setting `safari10: true` in `minify()`
                                for `mangle` and `format` options.
                                By default `terser` will not work around
                                Safari 10/11 bugs.
    --source-map [options]      Enable source map/specify source map options:
                                `base`  Path to compute relative paths from input files.
                                `content`  Input source map, useful if you're compressing
                                           JS that was generated from some other original
                                           code. Specify "inline" if the source map is
                                           included within the sources.
                                `filename`  Name and/or location of the output source.
                                `includeSources`  Pass this flag if you want to include
                                                  the content of source files in the
                                                  source map as sourcesContent property.
                                `root`  Path to the original source to be included in
                                        the source map.
                                `url`  If specified, path to the source map to append in
                                       `//# sourceMappingURL`.
    --timings                   Display operations run time on STDERR.
    --toplevel                  Compress and/or mangle variables in top level scope.
    --wrap <name>               Embed everything in a big function, making the
                                “exports” and “global” variables available. You
                                need to pass an argument to this option to
                                specify the name that your module will take
                                when included in, say, a browser.

Specify --output (-o) to declare the output file. Otherwise the output goes to STDOUT.

CLI source map options

Terser can generate a source map file, which is highly useful for debugging your compressed JavaScript. To get a source map, pass --source-map --output output.js (source map will be written out to output.js.map).

Additional options:

• --source-map "filename='<NAME>'" to specify the name of the source map.

• --source-map "root='<URL>'" to pass the URL where the original files can be found.

• --source-map "url='<URL>'" to specify the URL where the source map can be found. Otherwise Terser assumes HTTP X-SourceMap is being used and will omit the //# sourceMappingURL= directive.

For example:

terser js/file1.js js/file2.js \
         -o foo.min.js -c -m \
         --source-map "root='http://foo.com/src',url='foo.min.js.map'"

The above will compress and mangle file1.js and file2.js, will drop the output in foo.min.js and the source map in foo.min.js.map. The source mapping will refer to http://foo.com/src/js/file1.js and http://foo.com/src/js/file2.js (in fact it will list http://foo.com/src as the source map root, and the original files as js/file1.js and js/file2.js).

Composed source map

When you're compressing JS code that was output by a compiler such as CoffeeScript, mapping to the JS code won't be too helpful. Instead, you'd like to map back to the original code (i.e. CoffeeScript). Terser has an option to take an input source map. Assuming you have a mapping from CoffeeScript → compiled JS, Terser can generate a map from CoffeeScript → compressed JS by mapping every token in the compiled JS to its original location.

To use this feature pass --source-map "content='/path/to/input/source.map'" or --source-map "content=inline" if the source map is included inline with the sources.

CLI compress options

You need to pass --compress (-c) to enable the compressor. Optionally you can pass a comma-separated list of compress options.

Options are in the form foo=bar, or just foo (the latter implies a boolean option that you want to set true; it's effectively a shortcut for foo=true).

Example:

terser file.js -c toplevel,sequences=false

CLI mangle options

To enable the mangler you need to pass --mangle (-m). The following (comma-separated) options are supported:

• toplevel (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:

terser ... -m reserved=['
to prevent the require, exports and $ names from being changed.
CLI mangling property names (--mangle-props)
Note: THIS WILL BREAK YOUR CODE. A good rule of thumb is not to use this unless you know exactly what you're doing and how this works and read this section until the end.
Mangling property names is a separate step, different from variable name mangling.  Pass
--mangle-props to enable it. The least dangerous
way to use this is to use the regex option like so:
terser example.js -c -m --mangle-props regex=/_$/
This will mangle all properties that end with an
underscore. So you can use it to mangle internal methods.
By default, it will mangle all properties in the
input code with the exception of built in DOM properties and properties
in core JavaScript classes, which is what will break your code if you don't:

Control all the code you're mangling
Avoid using a module bundler, as they usually will call Terser on each file individually, making it impossible to pass mangled objects between modules.
Avoid calling functions like defineProperty or hasOwnProperty, because they refer to object properties using strings and will break your code if you don't know what you are doing.

An example:
// example.js
var x = {
    baz_: 0,
    foo_: 1,
    calc: function() {
        return this.foo_ + this.baz_;
    }
};
x.bar_ = 2;
x["baz_"] = 3;
console.log(x.calc());
Mangle all properties (except for JavaScript builtins) (very unsafe):
$ terser example.js -c passes=2 -m --mangle-props
var x={o:3,t:1,i:function(){return this.t+this.o},s:2};console.log(x.i());
Mangle all properties except for reserved properties (still very unsafe):
$ terser example.js -c passes=2 -m --mangle-props reserved=[foo_,bar_]
var x={o:3,foo_:1,t:function(){return this.foo_+this.o},bar_:2};console.log(x.t());
Mangle all properties matching a regex (not as unsafe but still unsafe):
$ terser example.js -c passes=2 -m --mangle-props regex=/_$/
var x={o:3,t:1,calc:function(){return this.t+this.o},i:2};console.log(x.calc());
Combining mangle properties options:
$ terser example.js -c passes=2 -m --mangle-props regex=/_$/,reserved=[bar_]
var x={o:3,t:1,calc:function(){return this.t+this.o},bar_:2};console.log(x.calc());
In order for this to be of any use, we avoid mangling standard JS names and DOM
API properties by default (--mangle-props builtins to override).
A regular expression can be used to define which property names should be
mangled.  For example, --mangle-props regex=/^_/ will only mangle property
names that start with an underscore.
When you compress multiple files using this option, in order for them to
work together in the end we need to ensure somehow that one property gets
mangled to the same name in all of them.  For this, pass --name-cache filename.json
and Terser will maintain these mappings in a file which can then be reused.
It should be initially empty.  Example:
$ rm -f /tmp/cache.json  # start fresh
$ terser file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js
$ terser file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js
Now, part1.js and part2.js will be consistent with each other in terms
of mangled property names.
Using the name cache is not necessary if you compress all your files in a
single call to Terser.
Mangling unquoted names (--mangle-props keep_quoted)
Using quoted property name (o["foo"]) reserves the property name (foo)
so that it is not mangled throughout the entire script even when used in an
unquoted style (o.foo). Example:
// stuff.js
var o = {
    "foo": 1,
    bar: 3
};
o.foo += o.bar;
console.log(o.foo);
$ terser stuff.js --mangle-props keep_quoted -c -m
var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo);
Debugging property name mangling
You can also pass --mangle-props debug in order to mangle property names
without completely obscuring them. For example the property o.foo
would mangle to o._$foo$_ with this option. This allows property mangling
of a large codebase while still being able to debug the code and identify
where mangling is breaking things.
$ terser stuff.js --mangle-props debug -c -m
var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_);
You can also pass a custom suffix using --mangle-props debug=XYZ. This would then
mangle o.foo to o._$foo$XYZ_. You can change this each time you compile a
script to identify how a property got mangled. One technique is to pass a
random number on every compile to simulate mangling changing with different
inputs (e.g. as you update the input script with new properties), and to help
identify mistakes like writing mangled keys to storage.
API Reference
Assuming installation via NPM, you can load Terser in your application
like this:
const { minify } = require("terser");
Or,
import { minify } from "terser";
Browser loading is also supported. It exposes a global variable Terser containing a .minify property:
<script src="https://cdn.jsdelivr.net/npm/source-map@0.7.3/dist/source-map.js"></script>
<script src="https://cdn.jsdelivr.net/npm/terser/dist/bundle.min.js"></script>
There is an async high level function, async minify(code, options),
which will perform all minification phases in a configurable
manner. By default minify() will enable compress
and mangle. Example:
var code = "function add(first, second) { return first + second; }";
var result = await minify(code, { sourceMap: true });
console.log(result.code);  // minified output: function add(n,d){return n+d}
console.log(result.map);  // source map
There is also a minify_sync() alternative version of it, which returns instantly.
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 = await 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 = await minify(code, options);
console.log(result.code);
// console.log(3+7);
The nameCache option:
var options = {
    mangle: {
        toplevel: true,
    },
    nameCache: {}
};
var result1 = await minify({
    "file1.js": "function add(first, second) { return first + second; }"
}, options);
var result2 = await 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", await minify({
    "file1.js": fs.readFileSync("file1.js", "utf8"),
    "file2.js": fs.readFileSync("file2.js", "utf8")
}, options).code, "utf8");
fs.writeFileSync("part2.js", await 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
    },
    format: {
        preamble: "/* minified */"
    }
};
var result = await minify(code, options);
console.log(result.code);
// /* minified */
// alert(10);"
An error example:
try {
    const result = await minify({"foo.js" : "if (0) else console.log(1);"});
    // Do something with result
} catch (error) {
    const { message, filename, line, col, pos } = error;
    // Do something with error
}
Minify options

ecma (default undefined) - pass 5, 2015, 2016, etc to override
compress and format's ecma options.

enclose (default false) - pass true, or a string in the format
of "args[:values]", where args and values are comma-separated
argument names and values, respectively, to embed the output in a big
function with the configurable arguments and values.

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.


module (default false) — Use when minifying an ES6 module. "use strict"
is implied and names can be mangled on the top scope. If compress or
mangle is enabled then the toplevel option will be enabled.

format or output (default null) — pass an object if you wish to specify
additional format 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. Pass a regular expression to only keep class names matching that regex.

keep_fnames (default: false) - pass true to prevent discarding or mangling
of function names. Pass a regular expression to only keep function names matching that regex.
Useful for code relying on Function.prototype.name. If the top level minify option
keep_classnames is undefined it will be overridden 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 format for details.


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

        properties: {
            // mangle property options
        }
    },
    format: {
        // format options (can also use `output` for backwards compatibility)
    },
    sourceMap: {
        // source map options
    },
    ecma: 5, // specify one of: 5, 2015, 2016, etc.
    enclose: false, // or specify true, or "args:values"
    keep_classnames: false,
    keep_fnames: false,
    ie8: false,
    module: false,
    nameCache: null, // or specify a name cache object
    safari10: false,
    toplevel: false
}
Source map options
To generate a source map:
var result = await 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 = await 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 = await 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.
If you happen to need the source map as a raw object, set sourceMap.asObject to true.
Parse options

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

html5_comments (default true)

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

spidermonkey (default false) -- accept a Spidermonkey (Mozilla) AST


Compress options

defaults (default: true) -- Pass false to disable most default
enabled compress transforms. Useful when you only want to enable a few
compress options while disabling the rest.

arrows (default: true) -- Class and object literal methods are converted
will also be converted to arrow expressions if the resultant code is shorter:
m(){return x} becomes m:()=>x. To do this to regular ES5 functions which
don't use this or arguments, see unsafe_arrows.

arguments (default: false) -- 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

booleans_as_integers (default: false) -- Turn booleans into 0 and 1, also
makes comparisons with booleans use == and != instead of === and !==.

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. Note: comparisons
works best with lhs_constants enabled.

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

directives (default: true) -- remove redundant or non-standard directives

drop_console (default: false) -- Pass true to discard calls to
console.* functions. If you only want to discard a portion of console, 
 you can pass an array like this ['log', 'info'], which will only discard console.log、 console.info.

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

ecma (default: 5) -- Pass 2015 or greater to enable compress options that
will transform ES5 code into smaller ES6+ equivalent forms.

builtins_ecma (default: 5) -- An ES version number (like ecma). Tells Terser which well-known functions, constants, methods and classes are available in the global object. Does nothing by itself, but is used by builtins_pure and unsafe.

builtins_pure (default: false) -- Pass true to assume that functions matched by the builtins_ecma option (such as Math.sin or unescape) are pure and calls to them can be removed.

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, let and const statements

keep_classnames (default: false) -- Pass true to prevent the compressor from
discarding class names. Pass a regular expression to only keep class names matching
that regex. 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. Pass a regular expression to only keep
function names matching that regex. 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.

lhs_constants (default: true) -- Moves constant values to the left-hand side
of binary nodes. foo == 42 → 42 == foo

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

module (default false) -- Pass true when compressing an ES6 module. Strict
mode is implied and the toplevel option as well.

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
Terser 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, Terser 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, Terser will assume that object property access
(e.g. foo.bar or foo["bar"]) doesn't have any side effects.
Specify "strict" to treat foo.bar as side-effect-free only when
foo is certain to not throw, i.e. not null or undefined.

pure_new (default: false) -- Set to true to assume new X() never has
side effects.

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

reduce_funcs (default: true) -- Inline single-use functions when
possible. Depends on reduce_vars being enabled.  Disabling this option
sometimes improves performance of the output code.

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) -- Remove expressions which have no side effects
and whose results aren't used.

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
(details).

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 2015 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. Or if one of two operands is NaN, the result is always
false. 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_symbols (default: false) -- removes keys from native Symbol
declarations, e.g Symbol("kDog") becomes Symbol().

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")


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.
Pass a regular expression to only keep class names matching that regex.
See also: the keep_classnames compress option.

keep_fnames (default false) -- Pass true to not mangle function names.
Pass a regular expression to only keep function names matching that regex.
Useful for code relying on Function.prototype.name. See also: the keep_fnames
compress option.

module (default false) -- Pass true an ES6 modules, where the toplevel
scope is not the global scope. Implies toplevel and assumes input code is strict mode JS.

nth_identifier (default: an internal mangler that weights based on character
frequency analysis) -- Pass an object with a get(n) function that converts an
ordinal into the nth most favored (usually shortest) identifier.
Optionally also provide reset(), sort(), and consider(chars, delta) to
use character frequency analysis of the source code.

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 format option.


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

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

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

await 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) — How quoting properties ({"prop": ...} and obj["prop"]) controls what gets mangled.

"strict" (recommended) -- obj.prop is mangled.
false -- obj["prop"] is mangled.
true -- obj.prop is mangled unless there is obj["prop"] elsewhere in the code.


nth_identifier (default: an internal mangler that weights based on character
frequency analysis) -- Pass an object with a get(n) function that converts an
ordinal into the nth most favored (usually shortest) identifier.
Optionally also provide reset(), sort(), and consider(chars, delta) to
use character frequency analysis of the source code.

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

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

undeclared (default: false) - Mangle those names when they are accessed
as properties of known top level variables but their declarations are never
found in input code. May be useful when only minifying parts of a project.
See #397 for more details.


Format options
These options control the format of Terser's output code. Previously known
as "output options".

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

beautify (default false) -- (DEPRECATED) whether to beautify the output.
When using the legacy -b CLI flag, this is set to true by default.

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

comments (default "some") -- by default it keeps JSDoc-style comments
that contain "@license", "@copyright", "@preserve" or start with !, pass true
or "all" to preserve all comments, false to omit comments in the output,
a regular expression string (e.g. /^!/) or a function.

ecma (default 5) -- set desired EcmaScript standard version for output.
Set ecma to 2015 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 your input will
still be output as is. For example: an ecma setting of 5 will not
convert modern code to ES5.

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_numbers (default false) -- keep number literals as it was in original code
 (disables optimizations like converting 1000000 into 1e6)

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 minified 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.

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


preserve_annotations -- (default false) -- Preserve Terser annotations in the output.

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 minified code (size before
gzip could be smaller; size after gzip insignificantly larger).

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

spidermonkey (default false) -- produce a Spidermonkey (Mozilla) AST

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

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

wrap_func_args (default false) -- pass true in order to wrap
function expressions that are passed as arguments, in parenthesis. See
OptimizeJS 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 comments starting with "!" and JSDoc-style comments that
contain "@preserve", "@copyright", "@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.  It assumes that standard
built-in ECMAScript functions and classes have not been altered or replaced.
You might want to try it on your own code; it should reduce the minified size.
Some examples of the optimizations made when this option is enabled:

new Array(1, 2, 3) or Array(1, 2, 3) → [ 1, 2, 3 ]
Array.from([1, 2, 3]) → [1, 2, 3]
new Object() → {}
String(exp) or exp.toString() → "" + exp
new Object/RegExp/Function/Error/Array (...) → we discard the new
"foo bar".substr(4) → "bar"

Conditional compilation
You can use the --define (-d) switch in order to declare global
variables that Terser will assume to be constants (unless defined in
scope).  For example if you pass --define DEBUG=false then, coupled with
dead code removal Terser 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.
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:
terser build/defines.js js/foo.js js/bar.js... -c
Terser 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 = await 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 Terser
to parse the value as an expression:
await minify("alert('hello');", {
    compress: {
        global_defs: {
            "@alert": "console.log"
        }
    }
}).code;
// returns: 'console.log("hello");'
Otherwise it would be replaced as string literal:
await minify("alert('hello');", {
    compress: {
        global_defs: {
            "alert": "console.log"
        }
    }
}).code;
// returns: '"console.log"("hello");'
Annotations
Annotations in Terser are a way to tell it to treat a certain function call differently. The following annotations are available:

/*@__INLINE__*/ - forces a function to be inlined somewhere.
/*@__NOINLINE__*/ - Makes sure the called function is not inlined into the call site.
/*@__PURE__*/ - Marks a function call as pure. That means, it can safely be dropped.
/*@__KEY__*/ - Marks a string literal as a property to also mangle it when mangling properties.
/*@__MANGLE_PROP__*/ - Opts-in an object property (or class field) for mangling, when the property mangler is enabled.

You can use either a @ sign at the start, or a #.
Here are some examples on how to use them:
/*@__INLINE__*/
function_always_inlined_here()

/*#__NOINLINE__*/
function_cant_be_inlined_into_here()

const x = /*#__PURE__*/i_am_dropped_if_x_is_not_used()

function lookup(object, key) { return object[key]; }
lookup({ i_will_be_mangled_too: "bar" }, /*@__KEY__*/ "i_will_be_mangled_too");
ESTree / SpiderMonkey AST
Terser has its own abstract syntax tree format; for
practical reasons
we can't easily change to using the SpiderMonkey AST internally.  However,
Terser 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 Terser to mangle and
compress that:
acorn file.js | terser -p spidermonkey -m -c
The -p spidermonkey option tells Terser 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.
spidermonkey is also available in minify as parse and format options to
accept and/or produce a spidermonkey 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, Terser 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 Terser's own parser.
Terser 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
Terser builds by 3 to 4 times.



d3.js
size
gzip size
time (s)



original
451,131
108,733
-


terser@3.7.5 mangle=false, compress=false
316,600
85,245
0.82


terser@3.7.5 mangle=true, compress=false
220,216
72,730
1.45


terser@3.7.5 mangle=true, compress=true
212,046
70,954
5.87


babili@0.1.4
210,713
72,140
12.64


babel-minify@0.4.3
210,321
72,242
48.67


babel-minify@0.5.0-alpha.01eac1c3
210,421
72,238
14.17


To enable fast minify mode from the CLI use:
terser file.js -m
To enable fast minify mode with the API use:
await 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 compress option and just use mangle.
When debugging, make sure you enable the "map scopes" feature to map mangled variable names back to their original names.
Without this, all variable values will be undefined. See https://github.com/terser/terser/issues/1367 for more details.




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()).
document.all is not == null
Assigning properties to a class doesn't have side effects and does not throw.

Build Tools and Adaptors using Terser
https://www.npmjs.com/browse/depended/terser
Replacing uglify-es with terser in a project using yarn
A number of JS bundlers and uglify wrappers are still using buggy versions
of uglify-es and have not yet upgraded to terser. If you are using yarn
you can add the following alias to your project's package.json file:
  "resolutions": {
    "uglify-es": "npm:terser"
  }
to use terser instead of uglify-es in all deeply nested dependencies
without changing any code.
Note: for this change to take effect you must run the following commands
to remove the existing yarn lock file and reinstall all packages:
$ rm -rf node_modules yarn.lock
$ yarn
Reporting issues
A minimal, reproducible example
You're expected to provide a [minimal reproducible example] of input code that will demonstrate your issue.
To get to this example, you can remove bits of your code and stop if your issue ceases to reproduce.
Obtaining the source code given to Terser
Because users often don't control the call to await minify() or its arguments, Terser provides a TERSER_DEBUG_DIR environment variable to make terser output some debug logs.
These logs will contain the input code and options of each minify() call.
TERSER_DEBUG_DIR=/tmp/terser-log-dir command-that-uses-terser
ls /tmp/terser-log-dir
terser-debug-123456.log
If you're not sure how to set an environment variable on your shell (the above example works in bash), you can try using cross-env:
> npx cross-env TERSER_DEBUG_DIR=/path/to/logs command-that-uses-terser
Stack traces
In the terser CLI we use source-map-support to produce good error stacks. In your own app, you're expected to enable source-map-support (read their docs) to have nice stack traces that will help you write good issues.
README.md Patrons:
note: You can support this project on patreon: [link] The Terser Patreon is shutting down in favor of opencollective. Check out PATRONS.md for our first-tier patrons.
These are the second-tier patrons. Great thanks for your support!

CKEditor 
38elements 

Contributors
Code Contributors
This project exists thanks to all the people who contribute. [Contribute].

Financial Contributors
Become a financial contributor and help us sustain our community. [Contribute]
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Support this project with your organization. Your logo will show up here with a link to your website. [Contribute]










,'require','exports']

to prevent the __INLINE_CODE_41__, __INLINE_CODE_42__ and __INLINE_CODE_43__ names from being changed.

CLI mangling property names (__INLINE_CODE_44__)

Note: THIS WILL BREAK YOUR CODE. A good rule of thumb is not to use this unless you know exactly what you're doing and how this works and read this section until the end.

Mangling property names is a separate step, different from variable name mangling. Pass __INLINE_CODE_45__ to enable it. The least dangerous way to use this is to use the __INLINE_CODE_46__ option like so:

__CODE_BLOCK_9__

This will mangle all properties that end with an underscore. So you can use it to mangle internal methods.

By default, it will mangle all properties in the input code with the exception of built in DOM properties and properties in core JavaScript classes, which is what will break your code if you don't:

1. Control all the code you're mangling
2. Avoid using a module bundler, as they usually will call Terser on each file individually, making it impossible to pass mangled objects between modules.
3. Avoid calling functions like __INLINE_CODE_47__ or __INLINE_CODE_48__, because they refer to object properties using strings and will break your code if you don't know what you are doing.

An example:

__CODE_BLOCK_10__

Mangle all properties (except for JavaScript __INLINE_CODE_49__) (very unsafe):

__CODE_BLOCK_11__ __CODE_BLOCK_12__

Mangle all properties except for __INLINE_CODE_50__ properties (still very unsafe):

__CODE_BLOCK_13__ __CODE_BLOCK_14__

Mangle all properties matching a __INLINE_CODE_51__ (not as unsafe but still unsafe):

__CODE_BLOCK_15__ __CODE_BLOCK_16__

Combining mangle properties options:

__CODE_BLOCK_17__ __CODE_BLOCK_18__

In order for this to be of any use, we avoid mangling standard JS names and DOM API properties by default (__INLINE_CODE_52__ to override).

A regular expression can be used to define which property names should be mangled. For example, __INLINE_CODE_53__ 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_54__ and Terser will maintain these mappings in a file which can then be reused. It should be initially empty. Example:

__CODE_BLOCK_19__

Now, __INLINE_CODE_55__ and __INLINE_CODE_56__ will be consistent with each other in terms of mangled property names.

Using the name cache is not necessary if you compress all your files in a single call to Terser.

Mangling unquoted names (__INLINE_CODE_57__)

Using quoted property name (__INLINE_CODE_58__) reserves the property name (__INLINE_CODE_59__) so that it is not mangled throughout the entire script even when used in an unquoted style (__INLINE_CODE_60__). Example:

__CODE_BLOCK_20__ __CODE_BLOCK_21__ __CODE_BLOCK_22__

Debugging property name mangling

You can also pass __INLINE_CODE_61__ in order to mangle property names without completely obscuring them. For example the property __INLINE_CODE_62__ would mangle to __INLINE_CODE_63__ 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_23__ __CODE_BLOCK_24__

You can also pass a custom suffix using __INLINE_CODE_64__. This would then mangle __INLINE_CODE_65__ to __INLINE_CODE_66__. 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 Terser in your application like this:

__CODE_BLOCK_25__

Or,

__CODE_BLOCK_26__

Browser loading is also supported. It exposes a global variable __INLINE_CODE_67__ containing a __INLINE_CODE_68__ property:

__CODE_BLOCK_27__

There is an async high level function, __INLINE_CODE_69__, which will perform all minification phases in a configurable manner. By default __INLINE_CODE_70__ will enable __INLINE_CODE_71__ and __INLINE_CODE_72__. Example:

__CODE_BLOCK_28__

There is also a __INLINE_CODE_73__ alternative version of it, which returns instantly.

You can __INLINE_CODE_74__ 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_29__

The __INLINE_CODE_75__ option:

__CODE_BLOCK_30__

The __INLINE_CODE_76__ option:

__CODE_BLOCK_31__

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

__CODE_BLOCK_32__

An example of a combination of __INLINE_CODE_77__ options:

__CODE_BLOCK_33__

An error example:

__CODE_BLOCK_34__

Minify options

• __INLINE_CODE_78__ (default __INLINE_CODE_79__) - pass __INLINE_CODE_80__, __INLINE_CODE_81__, __INLINE_CODE_82__, etc to override __INLINE_CODE_83__ and __INLINE_CODE_84__'s __INLINE_CODE_85__ options.

• __INLINE_CODE_86__ (default __INLINE_CODE_87__) - pass __INLINE_CODE_88__, or a string in the format of __INLINE_CODE_89__, where __INLINE_CODE_90__ and __INLINE_CODE_91__ are comma-separated argument names and values, respectively, to embed the output in a big function with the configurable arguments and values.

• __INLINE_CODE_92__ (default __INLINE_CODE_93__) — pass an object if you wish to specify some additional parse options.

• __INLINE_CODE_94__ (default __INLINE_CODE_95__) — pass __INLINE_CODE_96__ to skip compressing entirely. Pass an object to specify custom compress options.

• __INLINE_CODE_97__ (default __INLINE_CODE_98__) — pass __INLINE_CODE_99__ to skip mangling names, or pass an object to specify mangle options (see below).

  • __INLINE_CODE_100__ (default __INLINE_CODE_101__) — a subcategory of the mangle option. Pass an object to specify custom mangle property options.

• __INLINE_CODE_102__ (default __INLINE_CODE_103__) — Use when minifying an ES6 module. "use strict" is implied and names can be mangled on the top scope. If __INLINE_CODE_104__ or __INLINE_CODE_105__ is enabled then the __INLINE_CODE_106__ option will be enabled.

• __INLINE_CODE_107__ or __INLINE_CODE_108__ (default __INLINE_CODE_109__) — pass an object if you wish to specify additional format options. The defaults are optimized for best compression.

• __INLINE_CODE_110__ (default __INLINE_CODE_111__) - pass an object if you wish to specify source map options.

• __INLINE_CODE_112__ (default __INLINE_CODE_113__) - set to __INLINE_CODE_114__ if you wish to enable top level variable and function name mangling and to drop unused variables and functions.

• __INLINE_CODE_115__ (default __INLINE_CODE_116__) - pass an empty object __INLINE_CODE_117__ or a previously used __INLINE_CODE_118__ object if you wish to cache mangled variable and property names across multiple invocations of __INLINE_CODE_119__. Note: this is a read/write property. __INLINE_CODE_120__ 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_121__ (default __INLINE_CODE_122__) - set to __INLINE_CODE_123__ to support IE8.

• __INLINE_CODE_124__ (default: __INLINE_CODE_125__) - pass __INLINE_CODE_126__ to prevent discarding or mangling of class names. Pass a regular expression to only keep class names matching that regex.

• __INLINE_CODE_127__ (default: __INLINE_CODE_128__) - pass __INLINE_CODE_129__ to prevent discarding or mangling of function names. Pass a regular expression to only keep function names matching that regex. Useful for code relying on __INLINE_CODE_130__. If the top level minify option __INLINE_CODE_131__ is __INLINE_CODE_132__ it will be overridden with the value of the top level minify option __INLINE_CODE_133__.

• __INLINE_CODE_134__ (default: __INLINE_CODE_135__) - pass __INLINE_CODE_136__ to work around Safari 10/11 bugs in loop scoping and __INLINE_CODE_137__. See __INLINE_CODE_138__ options in __INLINE_CODE_139__ and __INLINE_CODE_140__ for details.

Minify options structure

__CODE_BLOCK_35__

Source map options

To generate a source map:

__CODE_BLOCK_36__

Note that the source map is not saved in a file, it's just returned in __INLINE_CODE_141__. The value passed for __INLINE_CODE_142__ is only used to set __INLINE_CODE_143__ in __INLINE_CODE_144__. The value of __INLINE_CODE_145__ is only used to set __INLINE_CODE_146__ attribute (see the spec) in source map file.

You can set option __INLINE_CODE_147__ to be __INLINE_CODE_148__ and source map will be appended to code.

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

__CODE_BLOCK_37__

If you're compressing compiled JavaScript and have a source map for it, you can use __INLINE_CODE_149__:

__CODE_BLOCK_38__

If you're using the __INLINE_CODE_150__ header instead, you can just omit __INLINE_CODE_151__.

If you happen to need the source map as a raw object, set __INLINE_CODE_152__ to __INLINE_CODE_153__.

Parse options

• __INLINE_CODE_154__ (default __INLINE_CODE_155__) -- support top level __INLINE_CODE_156__ statements

• __INLINE_CODE_157__ (default __INLINE_CODE_158__)

• __INLINE_CODE_159__ (default __INLINE_CODE_160__) -- support __INLINE_CODE_161__ as the first line

• __INLINE_CODE_162__ (default __INLINE_CODE_163__) -- accept a Spidermonkey (Mozilla) AST

Compress options

• __INLINE_CODE_164__ (default: __INLINE_CODE_165__) -- Pass __INLINE_CODE_166__ to disable most default enabled __INLINE_CODE_167__ transforms. Useful when you only want to enable a few __INLINE_CODE_168__ options while disabling the rest.

• __INLINE_CODE_169__ (default: __INLINE_CODE_170__) -- Class and object literal methods are converted will also be converted to arrow expressions if the resultant code is shorter: __INLINE_CODE_171__ becomes __INLINE_CODE_172__. To do this to regular ES5 functions which don't use __INLINE_CODE_173__ or __INLINE_CODE_174__, see __INLINE_CODE_175__.

• __INLINE_CODE_176__ (default: __INLINE_CODE_177__) -- replace __INLINE_CODE_178__ with function parameter name whenever possible.

• __INLINE_CODE_179__ (default: __INLINE_CODE_180__) -- various optimizations for boolean context, for example __INLINE_CODE_181__

• __INLINE_CODE_182__ (default: __INLINE_CODE_183__) -- Turn booleans into 0 and 1, also makes comparisons with booleans use __INLINE_CODE_184__ and __INLINE_CODE_185__ instead of __INLINE_CODE_186__ and __INLINE_CODE_187__.

• __INLINE_CODE_188__ (default: __INLINE_CODE_189__) -- Collapse single-use non-constant variables, side effects permitting.

• __INLINE_CODE_190__ (default: __INLINE_CODE_191__) -- apply certain optimizations to binary nodes, e.g. __INLINE_CODE_192__ (only when __INLINE_CODE_193__), attempts to negate binary nodes, e.g. __INLINE_CODE_194__ etc. Note: __INLINE_CODE_195__ works best with __INLINE_CODE_196__ enabled.

• __INLINE_CODE_197__ (default: __INLINE_CODE_198__) -- Transforms constant computed properties into regular ones: __INLINE_CODE_199__ is converted to __INLINE_CODE_200__.

• __INLINE_CODE_201__ (default: __INLINE_CODE_202__) -- apply optimizations for __INLINE_CODE_203__-s and conditional expressions

• __INLINE_CODE_204__ (default: __INLINE_CODE_205__) -- remove unreachable code

• __INLINE_CODE_206__ (default: __INLINE_CODE_207__) -- remove redundant or non-standard directives

• __INLINE_CODE_208__ (default: __INLINE_CODE_209__) -- Pass __INLINE_CODE_210__ to discard calls to __INLINE_CODE_211__ functions. If you only want to discard a portion of console, you can pass an array like this __INLINE_CODE_212__, which will only discard __INLINE_CODE_213__、 __INLINE_CODE_214__.

• __INLINE_CODE_215__ (default: __INLINE_CODE_216__) -- remove __INLINE_CODE_217__ statements

• __INLINE_CODE_218__ (default: __INLINE_CODE_219__) -- Pass __INLINE_CODE_220__ or greater to enable __INLINE_CODE_221__ options that will transform ES5 code into smaller ES6+ equivalent forms.

• __INLINE_CODE_222__ (default: __INLINE_CODE_223__) -- An ES version number (like __INLINE_CODE_224__). Tells Terser which well-known functions, constants, methods and classes are available in the global object. Does nothing by itself, but is used by __INLINE_CODE_225__ and __INLINE_CODE_226__.

• __INLINE_CODE_227__ (default: __INLINE_CODE_228__) -- Pass __INLINE_CODE_229__ to assume that functions matched by the __INLINE_CODE_230__ option (such as __INLINE_CODE_231__ or __INLINE_CODE_232__) are pure and calls to them can be removed.

• __INLINE_CODE_233__ (default: __INLINE_CODE_234__) -- attempt to evaluate constant expressions

• __INLINE_CODE_235__ (default: __INLINE_CODE_236__) -- Pass __INLINE_CODE_237__ to preserve completion values from terminal statements without __INLINE_CODE_238__, e.g. in bookmarklets.

• __INLINE_CODE_239__ (default: __INLINE_CODE_240__) -- see conditional compilation

• __INLINE_CODE_241__ (default: __INLINE_CODE_242__) -- hoist function declarations

• __INLINE_CODE_243__ (default: __INLINE_CODE_244__) -- hoist properties from constant object and array literals into regular variables subject to a set of constraints. For example: __INLINE_CODE_245__ is converted to __INLINE_CODE_246__. Note: __INLINE_CODE_247__ works best with __INLINE_CODE_248__ enabled, the __INLINE_CODE_249__ option __INLINE_CODE_250__ set to __INLINE_CODE_251__ or higher, and the __INLINE_CODE_252__ option __INLINE_CODE_253__ enabled.

• __INLINE_CODE_254__ (default: __INLINE_CODE_255__) -- hoist __INLINE_CODE_256__ declarations (this is __INLINE_CODE_257__ by default because it seems to increase the size of the output in general)

• __INLINE_CODE_258__ (default: __INLINE_CODE_259__) -- optimizations for if/return and if/continue

• __INLINE_CODE_260__ (default: __INLINE_CODE_261__) -- inline calls to function with simple/__INLINE_CODE_262__ statement:

  • __INLINE_CODE_263__ -- same as __INLINE_CODE_264__
  • __INLINE_CODE_265__ -- disabled inlining
  • __INLINE_CODE_266__ -- inline simple functions
  • __INLINE_CODE_267__ -- inline functions with arguments
  • __INLINE_CODE_268__ -- inline functions with arguments and variables
  • __INLINE_CODE_269__ -- same as __INLINE_CODE_270__

• __INLINE_CODE_271__ (default: __INLINE_CODE_272__) -- join consecutive __INLINE_CODE_273__, __INLINE_CODE_274__ and __INLINE_CODE_275__ statements

• __INLINE_CODE_276__ (default: __INLINE_CODE_277__) -- Pass __INLINE_CODE_278__ to prevent the compressor from discarding class names. Pass a regular expression to only keep class names matching that regex. See also: the __INLINE_CODE_279__ mangle option.

• __INLINE_CODE_280__ (default: __INLINE_CODE_281__) -- Prevents the compressor from discarding unused function arguments. You need this for code which relies on __INLINE_CODE_282__.

• __INLINE_CODE_283__ (default: __INLINE_CODE_284__) -- Pass __INLINE_CODE_285__ to prevent the compressor from discarding function names. Pass a regular expression to only keep function names matching that regex. Useful for code relying on __INLINE_CODE_286__. See also: the __INLINE_CODE_287__ mangle option.

• __INLINE_CODE_288__ (default: __INLINE_CODE_289__) -- Pass __INLINE_CODE_290__ to prevent __INLINE_CODE_291__ from being compressed into __INLINE_CODE_292__, which may cause performance issues on Chrome.

• __INLINE_CODE_293__ (default: __INLINE_CODE_294__) -- Moves constant values to the left-hand side of binary nodes. __INLINE_CODE_295__

• __INLINE_CODE_296__ (default: __INLINE_CODE_297__) -- optimizations for __INLINE_CODE_298__, __INLINE_CODE_299__ and __INLINE_CODE_300__ loops when we can statically determine the condition.

• __INLINE_CODE_301__ (default __INLINE_CODE_302__) -- Pass __INLINE_CODE_303__ when compressing an ES6 module. Strict mode is implied and the __INLINE_CODE_304__ option as well.

• __INLINE_CODE_305__ (default: __INLINE_CODE_306__) -- negate "Immediately-Called Function Expressions" where the return value is discarded, to avoid the parens that the code generator would insert.

• __INLINE_CODE_307__ (default: __INLINE_CODE_308__) -- 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_309__ (default: __INLINE_CODE_310__) -- rewrite property access using the dot notation, for example __INLINE_CODE_311__

• __INLINE_CODE_312__ (default: __INLINE_CODE_313__) -- You can pass an array of names and Terser 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_314__. If variable __INLINE_CODE_315__ is not used elsewhere, Terser will drop it, but will still keep the __INLINE_CODE_316__, not knowing what it does. You can pass __INLINE_CODE_317__ 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_318__ (default: __INLINE_CODE_319__) -- If you pass __INLINE_CODE_320__ for this, Terser will assume that object property access (e.g. __INLINE_CODE_321__ or __INLINE_CODE_322__) doesn't have any side effects. Specify __INLINE_CODE_323__ to treat __INLINE_CODE_324__ as side-effect-free only when __INLINE_CODE_325__ is certain to not throw, i.e. not __INLINE_CODE_326__ or __INLINE_CODE_327__.

• __INLINE_CODE_328__ (default: __INLINE_CODE_329__) -- Set to __INLINE_CODE_330__ to assume __INLINE_CODE_331__ never has side effects.

• __INLINE_CODE_332__ (default: __INLINE_CODE_333__) -- Improve optimization on variables assigned with and used as constant values.

• __INLINE_CODE_334__ (default: __INLINE_CODE_335__) -- Inline single-use functions when possible. Depends on __INLINE_CODE_336__ being enabled. Disabling this option sometimes improves performance of the output code.

• __INLINE_CODE_337__ (default: __INLINE_CODE_338__) -- 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_339__ then the default __INLINE_CODE_340__ limit is __INLINE_CODE_341__. Set option to __INLINE_CODE_342__ or __INLINE_CODE_343__ to disable. The smallest __INLINE_CODE_344__ length is __INLINE_CODE_345__. A __INLINE_CODE_346__ value of __INLINE_CODE_347__ is grandfathered to be equivalent to __INLINE_CODE_348__ and as such means __INLINE_CODE_349__. On rare occasions the default sequences limit leads to very slow compress times in which case a value of __INLINE_CODE_350__ or less is recommended.

• __INLINE_CODE_351__ (default: __INLINE_CODE_352__) -- Remove expressions which have no side effects and whose results aren't used.

• __INLINE_CODE_353__ (default: __INLINE_CODE_354__) -- de-duplicate and remove unreachable __INLINE_CODE_355__ branches

• __INLINE_CODE_356__ (default: __INLINE_CODE_357__) -- drop unreferenced functions (__INLINE_CODE_358__) and/or variables (__INLINE_CODE_359__) in the top level scope (__INLINE_CODE_360__ by default, __INLINE_CODE_361__ to drop both unreferenced functions and variables)

• __INLINE_CODE_362__ (default: __INLINE_CODE_363__) -- prevent specific toplevel functions and variables from __INLINE_CODE_364__ removal (can be array, comma-separated, RegExp or function. Implies __INLINE_CODE_365__)

• __INLINE_CODE_366__ (default: __INLINE_CODE_367__) -- Transforms __INLINE_CODE_368__ into __INLINE_CODE_369__. Note: recommend to set this value to __INLINE_CODE_370__ for IE10 and earlier versions due to known issues.

• __INLINE_CODE_371__ (default: __INLINE_CODE_372__) -- apply "unsafe" transformations (details).

• __INLINE_CODE_373__ (default: __INLINE_CODE_374__) -- Convert ES5 style anonymous function expressions to arrow functions if the function body does not reference __INLINE_CODE_375__. Note: it is not always safe to perform this conversion if code relies on the the function having a __INLINE_CODE_376__, which arrow functions lack. This transform requires that the __INLINE_CODE_377__ compress option is set to __INLINE_CODE_378__ or greater.

• __INLINE_CODE_379__ (default: __INLINE_CODE_380__) -- Reverse __INLINE_CODE_381__ and __INLINE_CODE_382__ to __INLINE_CODE_383__ and __INLINE_CODE_384__ 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_385__, or __INLINE_CODE_386__. This could cause change in execution order after operands in the comparison are switching. Or if one of two operands is __INLINE_CODE_387__, the result is always __INLINE_CODE_388__. Compression only works if both __INLINE_CODE_389__ and __INLINE_CODE_390__ are both set to true.

• __INLINE_CODE_391__ (default: __INLINE_CODE_392__) -- compress and mangle __INLINE_CODE_393__ when both __INLINE_CODE_394__ and __INLINE_CODE_395__ are string literals.

• __INLINE_CODE_396__ (default: __INLINE_CODE_397__) -- optimize numerical expressions like __INLINE_CODE_398__ into __INLINE_CODE_399__, which may give imprecise floating point results.

• __INLINE_CODE_400__ (default: __INLINE_CODE_401__) -- removes keys from native Symbol declarations, e.g __INLINE_CODE_402__ becomes __INLINE_CODE_403__.

• __INLINE_CODE_404__ (default: false) -- Converts __INLINE_CODE_405__ to __INLINE_CODE_406__. __INLINE_CODE_407__ must be set to __INLINE_CODE_408__ or greater to enable this transform. If __INLINE_CODE_409__ 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_410__ is not a constructor" TypeError should any code try to __INLINE_CODE_411__ the former function.

• __INLINE_CODE_412__ (default: __INLINE_CODE_413__) -- optimize expressions like __INLINE_CODE_414__ into __INLINE_CODE_415__

• __INLINE_CODE_416__ (default: __INLINE_CODE_417__) -- enable substitutions of variables with __INLINE_CODE_418__ values the same way as if they are constants.

• __INLINE_CODE_419__ (default: __INLINE_CODE_420__) -- substitute __INLINE_CODE_421__ if there is a variable named __INLINE_CODE_422__ in scope (variable name will be mangled, typically reduced to a single character)

• __INLINE_CODE_423__ (default: __INLINE_CODE_424__) -- drop unreferenced functions and variables (simple direct variable assignments do not count as references unless set to __INLINE_CODE_425__)

Mangle options

• __INLINE_CODE_426__ (default __INLINE_CODE_427__) -- Pass __INLINE_CODE_428__ to mangle names visible in scopes where __INLINE_CODE_429__ or __INLINE_CODE_430__ are used.

• __INLINE_CODE_431__ (default __INLINE_CODE_432__) -- Pass __INLINE_CODE_433__ to not mangle class names. Pass a regular expression to only keep class names matching that regex. See also: the __INLINE_CODE_434__ compress option.

• __INLINE_CODE_435__ (default __INLINE_CODE_436__) -- Pass __INLINE_CODE_437__ to not mangle function names. Pass a regular expression to only keep function names matching that regex. Useful for code relying on __INLINE_CODE_438__. See also: the __INLINE_CODE_439__ compress option.

• __INLINE_CODE_440__ (default __INLINE_CODE_441__) -- Pass __INLINE_CODE_442__ an ES6 modules, where the toplevel scope is not the global scope. Implies __INLINE_CODE_443__ and assumes input code is strict mode JS.

• __INLINE_CODE_444__ (default: an internal mangler that weights based on character frequency analysis) -- Pass an object with a __INLINE_CODE_445__ function that converts an ordinal into the nth most favored (usually shortest) identifier. Optionally also provide __INLINE_CODE_446__, __INLINE_CODE_447__, and __INLINE_CODE_448__ to use character frequency analysis of the source code.

• __INLINE_CODE_449__ (default __INLINE_CODE_450__) -- Pass an array of identifiers that should be excluded from mangling. Example: __INLINE_CODE_451__.

• __INLINE_CODE_452__ (default __INLINE_CODE_453__) -- Pass __INLINE_CODE_454__ to mangle names declared in the top level scope.

• __INLINE_CODE_455__ (default __INLINE_CODE_456__) -- Pass __INLINE_CODE_457__ to work around the Safari 10 loop iterator bug "Cannot declare a let variable twice". See also: the __INLINE_CODE_458__ format option.

Examples:

__CODE_BLOCK_39__ __CODE_BLOCK_40__

Mangle properties options

• __INLINE_CODE_459__ (default: __INLINE_CODE_460__) — Use __INLINE_CODE_461__ to allow the mangling of builtin DOM properties. Not recommended to override this setting.

• __INLINE_CODE_462__ (default: __INLINE_CODE_463__) — Mangle names with the original name still present. Pass an empty string __INLINE_CODE_464__ to enable, or a non-empty string to set the debug suffix.

• __INLINE_CODE_465__ (default: __INLINE_CODE_466__) — How quoting properties (__INLINE_CODE_467__ and __INLINE_CODE_468__) controls what gets mangled.

  • __INLINE_CODE_469__ (recommended) -- __INLINE_CODE_470__ is mangled.
  • __INLINE_CODE_471__ -- __INLINE_CODE_472__ is mangled.
  • __INLINE_CODE_473__ -- __INLINE_CODE_474__ is mangled unless there is __INLINE_CODE_475__ elsewhere in the code.

• __INLINE_CODE_476__ (default: an internal mangler that weights based on character frequency analysis) -- Pass an object with a __INLINE_CODE_477__ function that converts an ordinal into the nth most favored (usually shortest) identifier. Optionally also provide __INLINE_CODE_478__, __INLINE_CODE_479__, and __INLINE_CODE_480__ to use character frequency analysis of the source code.

• __INLINE_CODE_481__ (default: __INLINE_CODE_482__) — Pass a RegExp literal or pattern string to only mangle property matching the regular expression.

• __INLINE_CODE_483__ (default: __INLINE_CODE_484__) — Do not mangle property names listed in the __INLINE_CODE_485__ array.

• __INLINE_CODE_486__ (default: __INLINE_CODE_487__) - Mangle those names when they are accessed as properties of known top level variables but their declarations are never found in input code. May be useful when only minifying parts of a project. See #397 for more details.

Format options

These options control the format of Terser's output code. Previously known as "output options".

• __INLINE_CODE_488__ (default __INLINE_CODE_489__) -- escape Unicode characters in strings and regexps (affects directives with non-ascii characters becoming invalid)

• __INLINE_CODE_490__ (default __INLINE_CODE_491__) -- (DEPRECATED) whether to beautify the output. When using the legacy __INLINE_CODE_492__ CLI flag, this is set to true by default.

• __INLINE_CODE_493__ (default __INLINE_CODE_494__) -- always insert braces in __INLINE_CODE_495__, __INLINE_CODE_496__, __INLINE_CODE_497__, __INLINE_CODE_498__ or __INLINE_CODE_499__ statements, even if their body is a single statement.

• __INLINE_CODE_500__ (default __INLINE_CODE_501__) -- by default it keeps JSDoc-style comments that contain "@license", "@copyright", "@preserve" or start with __INLINE_CODE_502__, pass __INLINE_CODE_503__ or __INLINE_CODE_504__ to preserve all comments, __INLINE_CODE_505__ to omit comments in the output, a regular expression string (e.g. __INLINE_CODE_506__) or a function.

• __INLINE_CODE_507__ (default __INLINE_CODE_508__) -- set desired EcmaScript standard version for output. Set __INLINE_CODE_509__ to __INLINE_CODE_510__ or greater to emit shorthand object properties - i.e.: __INLINE_CODE_511__ instead of __INLINE_CODE_512__. The __INLINE_CODE_513__ option will only change the output in direct control of the beautifier. Non-compatible features in your input will still be output as is. For example: an __INLINE_CODE_514__ setting of __INLINE_CODE_515__ will not convert modern code to ES5.

• __INLINE_CODE_516__ (default __INLINE_CODE_517__)

• __INLINE_CODE_518__ (default __INLINE_CODE_519__) -- prefix all lines by that many spaces

• __INLINE_CODE_520__ (default __INLINE_CODE_521__) -- escape HTML comments and the slash in occurrences of __INLINE_CODE_522__ in strings

• __INLINE_CODE_523__ (default __INLINE_CODE_524__) -- keep number literals as it was in original code (disables optimizations like converting __INLINE_CODE_525__ into __INLINE_CODE_526__)

• __INLINE_CODE_527__ (default __INLINE_CODE_528__) -- when turned on, prevents stripping quotes from property names in object literals.

• __INLINE_CODE_529__ (default __INLINE_CODE_530__) -- maximum line length (for minified code)

• __INLINE_CODE_531__ (default __INLINE_CODE_532__) -- 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_533__ (default __INLINE_CODE_534__) -- pass __INLINE_CODE_535__ to quote all keys in literal objects

• __INLINE_CODE_536__ (default __INLINE_CODE_537__) -- preferred quote style for strings (affects quoted property names and directives as well):

  • __INLINE_CODE_538__ -- prefers double quotes, switches to single quotes when there are more double quotes in the string itself. __INLINE_CODE_539__ is best for gzip size.
  • __INLINE_CODE_540__ -- always use single quotes
  • __INLINE_CODE_541__ -- always use double quotes
  • __INLINE_CODE_542__ -- always use the original quotes

• __INLINE_CODE_543__ -- (default __INLINE_CODE_544__) -- Preserve Terser annotations in the output.

• __INLINE_CODE_545__ (default __INLINE_CODE_546__) -- set this option to __INLINE_CODE_547__ to work around the Safari 10/11 await bug. See also: the __INLINE_CODE_548__ mangle option.

• __INLINE_CODE_549__ (default __INLINE_CODE_550__) -- separate statements with semicolons. If you pass __INLINE_CODE_551__ then whenever possible we will use a newline instead of a semicolon, leading to more readable output of minified code (size before gzip could be smaller; size after gzip insignificantly larger).

• __INLINE_CODE_552__ (default __INLINE_CODE_553__) -- preserve shebang __INLINE_CODE_554__ in preamble (bash scripts)

• __INLINE_CODE_555__ (default __INLINE_CODE_556__) -- produce a Spidermonkey (Mozilla) AST

• __INLINE_CODE_557__ (default __INLINE_CODE_558__) -- enable workarounds for WebKit bugs. PhantomJS users should set this option to __INLINE_CODE_559__.

• __INLINE_CODE_560__ (default __INLINE_CODE_561__) -- pass __INLINE_CODE_562__ to wrap immediately invoked function expressions. See #640 for more details.

• __INLINE_CODE_563__ (default __INLINE_CODE_564__) -- pass __INLINE_CODE_565__ in order to wrap function expressions that are passed as arguments, in parenthesis. See OptimizeJS for more details.

Miscellaneous

Keeping copyright notices or other comments

You can pass __INLINE_CODE_566__ to retain certain comments in the output. By default it will keep comments starting with "!" and JSDoc-style comments that contain "@preserve", "@copyright", "@license" or "@cc_on" (conditional compilation for IE). You can pass __INLINE_CODE_567__ to keep all the comments, or a valid JavaScript regexp to keep only comments that match this regexp. For example __INLINE_CODE_568__ will keep comments like __INLINE_CODE_569__.

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

__CODE_BLOCK_41__

Even though it has "@preserve", the comment will be lost because the inner function __INLINE_CODE_570__ (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_571__ __INLINE_CODE_572__ option

It enables some transformations that might break code logic in certain contrived cases, but should be fine for most code. It assumes that standard built-in ECMAScript functions and classes have not been altered or replaced. You might want to try it on your own code; it should reduce the minified size. Some examples of the optimizations made when this option is enabled:

• __INLINE_CODE_573__ or __INLINE_CODE_574__ → __INLINE_CODE_575__
• __INLINE_CODE_576__ → __INLINE_CODE_577__
• __INLINE_CODE_578__ → __INLINE_CODE_579__
• __INLINE_CODE_580__ or __INLINE_CODE_581__ → __INLINE_CODE_582__
• __INLINE_CODE_583__ → we discard the __INLINE_CODE_584__
• __INLINE_CODE_585__ → __INLINE_CODE_586__

Conditional compilation

You can use the __INLINE_CODE_587__ (__INLINE_CODE_588__) switch in order to declare global variables that Terser will assume to be constants (unless defined in scope). For example if you pass __INLINE_CODE_589__ then, coupled with dead code removal Terser will discard the following from the output:

__CODE_BLOCK_42__

You can specify nested constants in the form of __INLINE_CODE_590__.

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_591__ file with the following:

__CODE_BLOCK_43__

and build your code like this:

__CODE_BLOCK_44__

Terser 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_592__ declarations if you use them. If you are targeting < ES6 environments which does not support __INLINE_CODE_593__, using __INLINE_CODE_594__ with __INLINE_CODE_595__ (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_596__ and is a compressor property:

__CODE_BLOCK_45__

To replace an identifier with an arbitrary non-constant expression it is necessary to prefix the __INLINE_CODE_597__ key with __INLINE_CODE_598__ to instruct Terser to parse the value as an expression:

__CODE_BLOCK_46__

Otherwise it would be replaced as string literal:

__CODE_BLOCK_47__

Annotations

Annotations in Terser are a way to tell it to treat a certain function call differently. The following annotations are available:

• __INLINE_CODE_599__ - forces a function to be inlined somewhere.
• __INLINE_CODE_600__ - Makes sure the called function is not inlined into the call site.
• __INLINE_CODE_601__ - Marks a function call as pure. That means, it can safely be dropped.
• __INLINE_CODE_602__ - Marks a string literal as a property to also mangle it when mangling properties.
• __INLINE_CODE_603__ - Opts-in an object property (or class field) for mangling, when the property mangler is enabled.

You can use either a __INLINE_CODE_604__ sign at the start, or a __INLINE_CODE_605__.

Here are some examples on how to use them:

__CODE_BLOCK_48__

ESTree / SpiderMonkey AST

Terser has its own abstract syntax tree format; for practical reasons we can't easily change to using the SpiderMonkey AST internally. However, Terser 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 Terser to mangle and compress that:

__CODE_BLOCK_49__

The __INLINE_CODE_606__ option tells Terser 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.

__INLINE_CODE_607__ is also available in __INLINE_CODE_608__ as __INLINE_CODE_609__ and __INLINE_CODE_610__ options to accept and/or produce a spidermonkey AST.

Use Acorn for parsing

More for fun, I added the __INLINE_CODE_611__ option which will use Acorn to do all the parsing. If you pass this option, Terser will __INLINE_CODE_612__.

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 Terser's own parser.

Terser 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_613__ to speed up Terser builds by 3 to 4 times.

d3.js	size	gzip size	time (s)
original	451,131	108,733	-
terser@3.7.5 mangle=false, compress=false	316,600	85,245	0.82
terser@3.7.5 mangle=true, compress=false	220,216	72,730	1.45
terser@3.7.5 mangle=true, compress=true	212,046	70,954	5.87
babili@0.1.4	210,713	72,140	12.64
babel-minify@0.4.3	210,321	72,242	48.67
babel-minify@0.5.0-alpha.01eac1c3	210,421	72,238	14.17

To enable fast minify mode from the CLI use:

__CODE_BLOCK_50__

To enable fast minify mode with the API use:

__CODE_BLOCK_51__

Source maps and debugging

Various __INLINE_CODE_614__ 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 __INLINE_CODE_615__ option and just use __INLINE_CODE_616__.

When debugging, make sure you enable the "map scopes" feature to map mangled variable names back to their original names.
Without this, all variable values will be __INLINE_CODE_617__. See https://github.com/terser/terser/issues/1367 for more details.

Compiler assumptions

To allow for better optimizations, the compiler makes various assumptions:

• __INLINE_CODE_618__ and __INLINE_CODE_619__ don't have side effects, and for built-in objects they have not been overridden.
• __INLINE_CODE_620__, __INLINE_CODE_621__ and __INLINE_CODE_622__ have not been externally redefined.
• __INLINE_CODE_623__, __INLINE_CODE_624__ and __INLINE_CODE_625__ are not used.
• The code doesn't expect the contents of __INLINE_CODE_626__ or __INLINE_CODE_627__ to be anything in particular.
• Getting and setting properties on a plain object does not cause other side effects (using __INLINE_CODE_628__ or __INLINE_CODE_629__).
• Object properties can be added, removed and modified (not prevented with __INLINE_CODE_630__, __INLINE_CODE_631__, __INLINE_CODE_632__, __INLINE_CODE_633__ or __INLINE_CODE_634__).
• __INLINE_CODE_635__ is not __INLINE_CODE_636__
• Assigning properties to a class doesn't have side effects and does not throw.

Build Tools and Adaptors using Terser

https://www.npmjs.com/browse/depended/terser

Replacing __INLINE_CODE_637__ with __INLINE_CODE_638__ in a project using __INLINE_CODE_639__

A number of JS bundlers and uglify wrappers are still using buggy versions of __INLINE_CODE_640__ and have not yet upgraded to __INLINE_CODE_641__. If you are using __INLINE_CODE_642__ you can add the following alias to your project's __INLINE_CODE_643__ file:

__CODE_BLOCK_52__

to use __INLINE_CODE_644__ instead of __INLINE_CODE_645__ in all deeply nested dependencies without changing any code.

Note: for this change to take effect you must run the following commands to remove the existing __INLINE_CODE_646__ lock file and reinstall all packages:

__CODE_BLOCK_53__

Reporting issues

A minimal, reproducible example

You're expected to provide a [minimal reproducible example] of input code that will demonstrate your issue.

To get to this example, you can remove bits of your code and stop if your issue ceases to reproduce.

Obtaining the source code given to Terser

Because users often don't control the call to __INLINE_CODE_647__ or its arguments, Terser provides a __INLINE_CODE_648__ environment variable to make terser output some debug logs.

These logs will contain the input code and options of each __INLINE_CODE_649__ call.

__CODE_BLOCK_54__

If you're not sure how to set an environment variable on your shell (the above example works in bash), you can try using cross-env:

__CODE_BLOCK_55__

Stack traces

In the terser CLI we use source-map-support to produce good error stacks. In your own app, you're expected to enable source-map-support (read their docs) to have nice stack traces that will help you write good issues.

README.md Patrons:

note: You can support this project on patreon: [link] The Terser Patreon is shutting down in favor of opencollective. Check out PATRONS.md for our first-tier patrons.

These are the second-tier patrons. Great thanks for your support!

• CKEditor
• 38elements

Contributors

Code Contributors

This project exists thanks to all the people who contribute. [Contribute].

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Individuals

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