• Become less conservative with analyzing function definitions for reduce_vars
  • Parse import.meta as a real AST node and not an


  • Correctly handle AST transform functions that mutate children arrays
  • Don’t mutate the options object passed to Terser (#1342)
  • Do not treat BigInt like a number


  • Keep (defaultArg = undefined) => ..., because default args don’t count for function length
  • Prevent inlining variables into ?. optional chains
  • Avoid removing unused arguments while transforming
  • Optimize iterating AST node lists
  • Make sure catch and finally aren’t children of try in the AST
  • Use modern unicode property escapes (\p{...}) to parse identifiers when available


  • Ensure function definitions, don’t assume the values of variables defined after them.


  • Fix sourcemaps with non-ascii characters (#1318)
  • Support string module name and export * as (#1336)
  • Do not move let out of for initializers, as it can change scoping
  • Fix a corner case that would generate the invalid syntax if (something) let x (“let” in braceless if body)
  • Knowledge of more native object properties (#1330)
  • Got rid of Travis (#1323)
  • Added semi-secret asObject sourcemap option to typescript defs (#1321)


  • Properly handle references in destructurings (const { [reference]: val } = ...)
  • Allow parsing of .#privatefield in nested classes
  • Do not evaluate operations that return large strings if that would make the output code larger
  • Make collapse_vars handle block scope correctly
  • Internal improvements: Typos (#1311), more tests, small-scale refactoring


  • Disallow private fields in object bodies (#1011)
  • Parse #privatefield in object (#1279)
  • Compress #privatefield in object


  • Fixed missing parentheses around optional chains
  • Avoid bare let or const as the bodies of if statements (#1253)
  • Small internal fixes (#1271)
  • Avoid inlining a class twice and creating two equivalent but !== classes.


  • Basic support for ES2022 class static initializer blocks.
  • Add AudioWorkletNode constructor options to domprops list (#1230)
  • Make identity function inliner not inline id(...expandedArgs)


  • Security fix for RegExps that should not be evaluated (regexp DDOS)
  • Source maps improvements (#1211)
  • Performance improvements in long property access evaluation (#1213)


  • keep_numbers option added to TypeScript defs (#1208)
  • Fixed parsing of nested template strings (#1204)


  • Switched to @jridgewell/source-map for sourcemap generation (#1190, #1181)
  • Fixed source maps with non-terminated segments (#1106)
  • Enabled typescript types to be imported from the package (#1194)
  • Extra DOM props have been added (#1191)
  • Delete the AST while generating code, as a means to save RAM


  • Removed self-assignments (varname=varname) (closes #1081)
  • Separated inlining code (for inlining things into references, or removing IIFEs)
  • Allow multiple identifiers with the same name in var destructuring (eg var { a, a } = x) (#1176)


  • All calls to eval() were removed (#1171, #1184)
  • source-map was updated to 0.8.0-beta.0 (#1164)
  • NavigatorUAData was added to domprops to avoid property mangling (#1166)


  • Fixed an issue with function definitions inside blocks (#1155)
  • Fixed parens of new in some situations (closes #1159)


  • TERSER_DEBUG_DIR environment variable
  • @copyright comments are now preserved with the comments=”some” option (#1153)


  • Unicode code point escapes (\u{abcde}) are not emitted inside RegExp literals anymore (#1147)
  • acorn is now a regular dependency


  • Massive optimization to max_line_len (#1109)
  • Basic support for import assertions
  • Marked ES2022 Object.hasOwn as a pure function
  • Fix delete optional?.property
  • New CI/CD pipeline with github actions (#1057)
  • Fix reordering of switch branches (#1092), (#1084)
  • Fix error when creating a class property called get
  • Acorn dependency is now an optional peerDependency
  • Fix mangling collision with exported variables (#1072)
  • Fix an issue with return someVariable = (async () => { ... })() (#1073)


  • Collapsing switch cases with the same bodies (even if they’re not next to each other) (#1070).
  • Fix evaluation of optional chain expressions (#1062)
  • Fix mangling collision in ESM exports (#1063)
  • Fix issue with mutating function objects after a second pass (#1047)
  • Fix for inlining object spread { ...obj } (#1071)
  • Typescript typings fix (#1069)


  • Fixed shadowing variables while moving code in some cases (#1065)
  • Stop mangling computed & quoted properties when keep_quoted is enabled.
  • Fix for mangling private getter/setter and .#private access (#1060, #1068)
  • Array.from has a new optimization when the unsafe option is set (#737)
  • Mangle/propmangle let you generate your own identifiers through the nth_identifier option (#1061)
  • More optimizations to switch statements (#1044)


  • Fixed issues with compressing functions defined in global_defs option (#1036)
  • New recipe for using Terser in gulp was added to (#1035)
  • Fixed issues with ?? and ?. (#1045)
  • Future reserved words such as package no longer require you to disable strict mode to be used as names.
  • Refactored huge compressor file into multiple more focused files.
  • Avoided unparenthesized in operator in some for loops (it breaks parsing because of loops)
  • Improved documentation (#1021, #1025)
  • More type definitions (#1021)


  • Avoided collapsing assignments together if it would place a chain assignment on the left hand side, which is invalid syntax (a?.b = c)
  • Removed undefined from object expansions ({ ...void 0 } -> {})
  • Fix crash when checking if something is nullish or undefined (#1009)
  • Fixed comparison of private class properties (#1015)
  • Minor performance improvements (#993)
  • Fixed scope of function defs in strict mode (they are block scoped)


  • Several compile-time evaluation and inlining fixes
  • Allow reduce_funcs to be disabled again.
  • Add spidermonkey options to parse and format (#974)
  • Accept {get = "default val"} and {set = "default val"} in destructuring arguments.
  • Change package.json export map to help require.resolve (#971)
  • Improve docs
  • Fix export default of an anonymous class with extends


  • Mark assignments to the .prototype of a class as pure
  • Parenthesize await on the left of ** (while accepting legacy non-parenthesised input)
  • Avoided outputting NUL bytes in optimized RegExps, to stop the output from breaking other tools
  • Added exports to domprops (#939)
  • Fixed a crash when spreading ...this
  • Fixed the computed size of arrow functions, which improves their inlining


  • Added top-level await
  • Beautify option has been removed in #895
  • Private properties, getters and setters have been added in #913 and some more commits
  • Docs improvements: #896, #903, #916


  • Fixed object properties with unicode surrogates on safari.


  • Fixed crash when inlining uninitialized variable into template string.
  • The sourcemap for dist was removed for being too large.


  • Logical assignment
  • Change let x = undefined to just let x
  • Removed some optimizations for template strings, placing them behind unsafe options. Reason: adding strings is not equivalent to template strings, due to valueOf differences.
  • The AST_Token class was slimmed down in order to use less memory.


  • Restore node 13 support


Hotfix release, fixes package.json “engines” syntax


  • Fixed parentheses when outputting ?? mixed with || and &&
  • Improved hygiene of the symbol generator


  • Avoid moving named functions into default exports.
  • Enabled transform() for chain expressions. This allows AST transformers to reach inside chain expressions.


  • Fixed a crash when hoisting (with hoist_vars) a destructuring variable declaration


  • source-map library has been updated, bringing memory usage and CPU time improvements when reading input source maps (the SourceMapConsumer is now WASM based).
  • The wrap_func_args option now also wraps arrow functions, as opposed to only function expressions.


  • Prevented spread operations from being expanded when the expanded array/object contains getters, setters, or array holes.
  • Fixed very slow self-recursion in some cases of removing extraneous parentheses from + operations.


  • An issue with destructuring declarations when pure_getters is enabled has been fixed
  • Fixed a crash when chain expressions need to be shallowly compared
  • Made inlining functions more conservative to make sure a function that contains a reference to itself isn’t moved into a place that can create multiple instances of itself.


  • Fixed a crash when compressing object spreads in some cases
  • Fixed compiletime evaluation of optional chains (caused typeof a?.b to always return “object”)
  • domprops has been updated to contain every single possible prop


  • The parse step now doesn’t accept an ecma option, so that all ES code is accepted.
  • Optional dotted chains now accept keywords, just like dotted expressions (foo?.default)


  • Optional chaining syntax is now supported.
  • Consecutive await expressions don’t have unnecessary parens
  • Taking the variable name’s length (after mangling) into consideration when deciding to inline


  • import.meta is now supported
  • Typescript typings have been improved


  • in operator now taken into account during property mangle.
  • Fixed infinite loop in face of a reference loop in some situations.
  • Kept exports and imports around even if there’s something which will throw before them.
  • The main exported bundle for commonjs, dist/bundle.min.js is no longer minified.


  • BREAKING: minify() is now async and rejects a promise instead of returning an error.
  • BREAKING: Internal AST is no longer exposed, so that it can be improved without releasing breaking changes.
  • BREAKING: Lowest supported node version is 10
  • BREAKING: There are no more warnings being emitted
  • Module is now distributed as a dual package - You can import and require() too.
  • Inline improvements were made

v4.8.1 (backport)

  • Security fix for RegExps that should not be evaluated (regexp DDOS)


  • Support for numeric separators (million = 1_000_000) was added.
  • Assigning properties to a class is now assumed to be pure.
  • Fixed bug where yield wasn’t considered a valid property key in generators.


  • A bug was fixed where an arrow function would have the wrong size
  • arguments object is now considered safe to retrieve properties from (useful for length, or 0) even when pure_getters is not set.
  • Fixed erroneous const declarations without value (which is invalid) in some corner cases when using collapse_vars.


  • Fixed issue where ES5 object properties were being turned into ES6 object properties due to more lax unicode rules.
  • Fixed parsing of BigInt with lowercase e in them.


  • Fixed subtree comparison code, making it see that [1,[2, 3]] is different from [1, 2, [3]]
  • Printing of unicode identifiers has been improved


  • Read unused classes’ properties and method keys, to figure out if they use other variables.
  • Prevent inlining into block scopes when there are name collisions
  • Functions are no longer inlined into parameter defaults, because they live in their own special scope.
  • When inlining identity functions, take into account the fact they may be used to drop this in function calls.
  • Nullish coalescing operator (x ?? y), plus basic optimization for it.
  • Template literals in binary expressions such as + have been further optimized


  • Do not use reduce_vars when classes are present


  • Check if block scopes actually exist in blocks


  • Take into account “executed bits” of classes like static properties or computed keys, when checking if a class evaluation might throw or have side effects.


  • Some new performance gains through a AST_Node.size() method which measures a node’s source code length without printing it to a string first.
  • An issue with setting --comments to false in the CLI has been fixed.
  • Fixed some issues with inlining
  • unsafe_symbols compress option was added, which turns Symbol("name") into just Symbol()
  • Brought back compress performance improvement through the AST_Node.equivalent_to(other) method (which was reverted in v4.6.6).


(hotfix release)

  • Reverted code to 4.6.4 to allow for more time to investigate an issue.

v4.6.5 (REVERTED)

  • Improved compress performance through using a new method to see if two nodes are equivalent, instead of printing them to a string.


  • The "some" value in the comments output option now preserves @lic and other important comments when using //
  • </script> is now better escaped in regex, and in comments, when using the inline_script output option
  • Fixed an issue when transforming new RegExp into /.../ when slashes are included in the source
  • AST_Node.prototype.constructor now exists, allowing for easier debugging of crashes
  • Multiple if statements with the same consequents are now collapsed
  • Typescript typings improvements
  • Optimizations while looking for surrogate pairs in strings


  • Annotations such as /*#__NOINLINE__*/ and /*#__PURE__*/ may now be preserved using the preserve_annotations output option
  • A TypeScript definition update for the keep_quoted output option.


  • A bug where functions were inlined into other functions with scope conflicts has been fixed.
  • /*#__NOINLINE__*/ annotation fixed for more use cases where inlining happens.


  • Fixed an issue where a class is duplicated by reduce_vars when there’s a recursive reference to the class.


  • Fixed issues with recursive class references.
  • BigInt evaluation has been prevented, stopping Terser from evaluating BigInts like it would do regular numbers.
  • Class property support has been added


(hotfix release)

  • Fixed issue where () => ({})[something] was not parenthesised correctly.


  • Inlining has been improved
  • An issue where keep_fnames combined with functions declared through variables was causing name shadowing has been fixed
  • You can now set the ES version through their year
  • The output option keep_numbers has been added, which prevents Terser from turning 1000 into 1e3 and such
  • Internal small optimisations and refactors


  • Number and BigInt parsing has been fixed
  • /*#__INLINE__*/ annotation fixed for arrow functions with non-block bodies.
  • Functional tests have been added, using this repository.
  • A memory leak, where the entire AST lives on after compression, has been plugged.


  • Fixed a problem with inlining identity functions


note: This introduced a feature, therefore it should have been a minor release.

  • Fixed a crash when unsafe was enabled.
  • An issue has been fixed where let statements might be collapsed out of their scope.
  • Some error messages have been improved by adding quotes around variable names.


  • Added /*#__INLINE__*/ and /*#__NOINLINE__*/ annotations for calls. If a call has one of these, it either forces or forbids inlining.


  • Fixed a problem where window was considered safe to access, even though there are situations where it isn’t (Node.js, workers…)
  • Fixed an error where ++ and -- were considered side-effect free
  • Number(x) now needs both unsafe and and unsafe_math to be compressed into +x because x might be a BigInt
  • keep_fnames now correctly supports regexes when the function is in a variable declaration


  • Fixed syntax error when repeated semicolons were encountered in classes
  • Fixed invalid output caused by the creation of empty sequences internally
  • Scopes are now updated when scopes are inlined into them


  • Fixed issue with mangle’s keep_fnames option, introduced when adding code to keep variable names of anonymous functions


  • Typescript typings fix


  • Parsing of regex options in the CLI (which broke in v4.3.5) was fixed.
  • typescript definition updates


(crash hotfix)


  • Fixed an issue with DOS line endings strings separated by \ and a new line.
  • Improved fix for the output size regression related to unused references within the extends section of a class.
  • Variable names of anonymous functions (eg: const x = () => { ... } or var func = function () {...}) are now preserved when keep_fnames is true.
  • Fixed performance degradation introduced for large payloads in v4.2.0


  • Fixed a regression where the output size was increased when unused classes were referred to in the extends clause of a class.
  • Small typescript typings fixes.
  • Comments with @preserve, @license, @cc_on as well as comments starting with /*! and /**! are now preserved by default.


  • Fixed a problem where parsing template strings would mix up octal notation and a slash followed by a zero representing a null character.
  • Started accepting the name async in destructuring arguments with default value.
  • Now Terser takes into account side effects inside class extends clauses.
  • Added parens whenever there’s a comment between a return statement and the returned value, to prevent issues with ASI.
  • Stopped using raw RegExp objects, since the spec is going to continue to evolve. This ensures Terser is able to process new, unknown RegExp flags and features. This is a breaking change in the AST node AST_RegExp.


  • Typescript typing fix
  • Ensure that functions can’t be inlined, by reduce_vars, into places where they’re accessing variables with the same name, but from somewhere else.


  • Fixed an issue from 4.3.0 where any block scope within a for loop erroneously had its parent set to the function scopee
  • Fixed an issue where compressing IIFEs with argument expansions would result in some parameters becoming undefined
  • addEventListener options argument’s properties are now part of the DOM properties list.


  • Do not drop computed object keys with side effects
  • Functions passed to other functions in calls are now wrapped in parentheses by default, which speeds up loading most modules
  • Objects with computed properties are now less likely to be hoisted
  • Speed and memory efficiency optimizations
  • Fixed scoping issues with try and switch


  • Minor refactors
  • Fixed a bug similar to #369 in collapse_vars
  • Functions can no longer be inlined into a place where they’re going to be compared with themselves.
  • reduce_funcs option is now legacy, as using reduce_vars without reduce_funcs caused some weird corner cases. As a result, it is now implied in reduce_vars and can’t be turned off without turning off reduce_vars.
  • Bug which would cause a random stack overflow has now been fixed.


  • When the source map URL is inline, don’t write it to a file.
  • Fixed output parens when a lambda literal is the tag on a tagged template string.
  • The option was added. This enables the property mangler to mangle properties of variables which can be found in the name cache, but whose properties are not known to this Terser run.
  • The v8 bug where the toString and source representations of regexes like RegExp("\\\n") includes an actual newline is now fixed.
  • Now we’re guaranteed to not have duplicate comments in the output
  • Domprops updates


  • Fixed a crash when inlining a function into somewhere else when it has interdependent, non-removable variables.


  • Several issues with the reduce_vars option were fixed.
  • Starting this version, we only have a dist/bundle.min.js


  • The hotfix was hotfixed


  • Fixed a bug where toplevel scopes were being mixed up with lambda scopes


  • Internal functions were replaced by Object.assign, Array.prototype.some, Array.prototype.find and Array.prototype.every.
  • A serious issue where some ESM-native code was broken was fixed.
  • Performance improvements were made.
  • Support for BigInt was added.
  • Inline efficiency was improved. Functions are now being inlined more proactively instead of being inlined only after another Compressor pass.


(Hotfix release. Reverts unmapped segments PR #342, which will be put back on Terser when the upstream issue is resolved)


  • Collisions between the arguments of inlined functions and names in the outer scope are now being avoided while inlining
  • Unmapped segments are now preserved when compressing a file which has source maps
  • Default values of functions are now correctly converted from Mozilla AST to Terser AST
  • JSON ⊂ ECMAScript spec (if you don’t know what this is you don’t need to)
  • Export AST_* classes to library users
  • Fixed issue with collapse_vars when functions are created with the same name as a variable which already exists
  • Added MutationObserverInit (Object with options for initialising a mutation observer) properties to the DOM property list
  • Custom Error subclasses are now internally used instead of old-school Error inheritance hacks.
  • Documentation fixes
  • Performance optimizations


  • breaking change: The variables property of all scopes has become a standard JavaScript Map as opposed to the old bespoke Dictionary object.
  • Typescript definitions were fixed
  • terser --help was fixed
  • The public interface was cleaned up
  • Fixed optimisation of Array and new Array
  • Added the keep_quoted=strict mode to mangle_props, which behaves more like Google Closure Compiler by mangling all unquoted property names, instead of reserving quoted property names automatically.
  • Fixed parent functions’ parameters being shadowed in some cases
  • Allowed Terser to run in a situation where there are custom functions attached to Object.prototype
  • And more bug fixes, optimisations and internal changes


  • More DOM properties added to –mangle-properties’s DOM property list
  • Closed issue where if 2 functions had the same argument name, Terser would not inline them together properly
  • Fixed issue with
  • You can now list files to minify in a Terser config file
  • Started replacing new Array(<number>) with an array literal
  • Started using ES6 capabilities like Set and the includes method for strings and arrays


  • Fixed issue where Terser being imported with import would cause it not to work due to the __esModule property. (PR #254 was submitted, which was nice, but since it wasn’t a pure commonJS approach I decided to go with my own solution)


  • No longer leaves names like Array or Object or window as a SimpleStatement (statement which is just a single expression).
  • Add support for sections sourcemaps (IndexedSourceMapConsumer)
  • Drops node.js v4 and starts using commonJS
  • Is now built with rollup


  • Inlined spread syntax ([...[1, 2, 3], 4, 5] => [1, 2, 3, 4, 5]) in arrays and objects.
  • Fixed typo in compressor warning
  • Fixed inline source map input bug
  • Fixed parsing of template literals with unnecessary escapes (Like \\a)