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  • 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 βŠ‚ 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)
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