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Options

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.

  • 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.