## 8.17.0 (2026-06-11)

### New features

The new `strict` option can be used to start script sources in strict mode.

### Bug fixes

Fix a number of corner case bugs when `using` or `await using` appear in `for` loop specs.

Disallow `new super()` expressions.

Don't allow the conditional in a ternary expression to be a (naked) arrow function.

## 8.16.0 (2026-02-19)

### New features

The `sourceType` option can now be set to `"commonjs"` to have the parser treat the top level scope as a function scope.

Add support for Unicode 17.

### Bug fixes

Don't recognize `await using` as contextual keywords when followed directly by a backslash.

Fix an issue where the parser would allow `return` statements in `static` blocks when `allowReturnOutsideFunction` was enabled.

Properly reject `using` declarations that appear directly in `switch` or `for` head scopes.

Fix some corner case issues in the recognition of `using` syntax.

## 8.15.0 (2025-06-08)

### New features

Support `using` and `await using` syntax.

The `AnyNode` type is now defined in such a way that plugins can extend it.

### Bug fixes

Fix an issue where the `bigint` property of literal nodes for non-decimal bigints had the wrong format.

The `acorn` CLI tool no longer crashes when emitting a tree that contains a bigint.

## 8.14.1 (2025-03-05)

### Bug fixes

Fix an issue where `await` expressions in class field initializers were inappropriately allowed.

Properly allow await inside an async arrow function inside a class field initializer.

Mention the source file name in syntax error messages when given.

Properly add an empty `attributes` property to every form of `ExportNamedDeclaration`.

## 8.14.0 (2024-10-27)

### New features

Support ES2025 import attributes.

Support ES2025 RegExp modifiers.

### Bug fixes

Support some missing Unicode properties.

## 8.13.0 (2024-10-16)

### New features

Upgrade to Unicode 16.0.

## 8.12.1 (2024-07-03)

### Bug fixes

Fix a regression that caused Acorn to no longer run on Node versions <8.10.

## 8.12.0 (2024-06-14)

### New features

Support ES2025 duplicate capture group names in regular expressions.

### Bug fixes

Include `VariableDeclarator` in the `AnyNode` type so that walker objects can refer to it without getting a type error.

Properly raise a parse error for invalid `for`/`of` statements using `async` as binding name.

Properly recognize \"use strict\" when preceded by a string with an escaped newline.

Mark the `Parser` constructor as protected, not private, so plugins can extend it without type errors.

Fix a bug where some invalid `delete` expressions were let through when the operand was parenthesized and `preserveParens` was enabled.

Properly normalize line endings in raw strings of invalid template tokens.

Properly track line numbers for escaped newlines in strings.

Fix a bug that broke line number accounting after a template literal with invalid escape sequences.

## 8.11.3 (2023-12-29)

### Bug fixes

Add `Function` and `Class` to the `AggregateType` type, so that they can be used in walkers without raising a type error.

Make sure `onToken` get an `import` keyword token when parsing `import.meta`.

Fix a bug where `.loc.start` could be undefined for `new.target` `meta` nodes.

## 8.11.2 (2023-10-27)

### Bug fixes

Fix a bug that caused regular expressions after colon tokens to not be properly tokenized in some circumstances.

## 8.11.1 (2023-10-26)

### Bug fixes

Fix a regression where `onToken` would receive 'name' tokens for 'new' keyword tokens.

## 8.11.0 (2023-10-26)

### Bug fixes

Fix an issue where tokenizing (without parsing) an object literal with a property named `class` or `function` could, in some circumstance, put the tokenizer into an invalid state.

Fix an issue where a slash after a call to a propery named the same as some keywords would be tokenized as a regular expression.

### New features

Upgrade to Unicode 15.1.

Use a set of new, much more precise, TypeScript types.

## 8.10.0 (2023-07-05)

### New features

Add a `checkPrivateFields` option that disables strict checking of private property use.

## 8.9.0 (2023-06-16)

### Bug fixes

Forbid dynamic import after `new`, even when part of a member expression.

### New features

Add Unicode properties for ES2023.

Add support for the `v` flag to regular expressions.

## 8.8.2 (2023-01-23)

### Bug fixes

Fix a bug that caused `allowHashBang` to be set to false when not provided, even with `ecmaVersion >= 14`.

Fix an exception when passing no option object to `parse` or `new Parser`.

Fix incorrect parse error on `if (0) let\n[astral identifier char]`.

## 8.8.1 (2022-10-24)

### Bug fixes

Make type for `Comment` compatible with estree types.

## 8.8.0 (2022-07-21)

### Bug fixes

Allow parentheses around spread args in destructuring object assignment.

Fix an issue where the tree contained `directive` properties in when parsing with a language version that doesn't support them.

### New features

Support hashbang comments by default in ECMAScript 2023 and later.

## 8.7.1 (2021-04-26)

### Bug fixes

Stop handling `"use strict"` directives in ECMAScript versions before 5.

Fix an issue where duplicate quoted export names in `export *` syntax were incorrectly checked.

Add missing type for `tokTypes`.

## 8.7.0 (2021-12-27)

### New features

Support quoted export names.

Upgrade to Unicode 14.

Add support for Unicode 13 properties in regular expressions.

### Bug fixes

Use a loop to find line breaks, because the existing regexp search would overrun the end of the searched range and waste a lot of time in minified code.

## 8.6.0 (2021-11-18)

### Bug fixes

Fix a bug where an object literal with multiple `__proto__` properties would incorrectly be accepted if a later property value held an assigment.

### New features

Support class private fields with the `in` operator.

## 8.5.0 (2021-09-06)

### Bug fixes

Improve context-dependent tokenization in a number of corner cases.

Fix location tracking after a 0x2028 or 0x2029 character in a string literal (which before did not increase the line number).

Fix an issue where arrow function bodies in for loop context would inappropriately consume `in` operators.

Fix wrong end locations stored on SequenceExpression nodes.

Implement restriction that `for`/`of` loop LHS can't start with `let`.

### New features

Add support for ES2022 class static blocks.

Allow multiple input files to be passed to the CLI tool.

## 8.4.1 (2021-06-24)

### Bug fixes

Fix a bug where `allowAwaitOutsideFunction` would allow `await` in class field initializers, and setting `ecmaVersion` to 13 or higher would allow top-level await in non-module sources.

## 8.4.0 (2021-06-11)

### New features

A new option, `allowSuperOutsideMethod`, can be used to suppress the error when `super` is used in the wrong context.

## 8.3.0 (2021-05-31)

### New features

Default `allowAwaitOutsideFunction` to true for ECMAScript 2022 an higher.

Add support for the `d` ([indices](https://github.com/tc39/proposal-regexp-match-indices)) regexp flag.

## 8.2.4 (2021-05-04)

### Bug fixes

Fix spec conformity in corner case 'for await (async of ...)'.

## 8.2.3 (2021-05-04)

### Bug fixes

Fix an issue where the library couldn't parse 'for (async of ...)'.

Fix a bug in UTF-16 decoding that would read characters incorrectly in some circumstances.

## 8.2.2 (2021-04-29)

### Bug fixes

Fix a bug where a class field initialized to an async arrow function wouldn't allow await inside it. Same issue existed for generator arrow functions with yield.

## 8.2.1 (2021-04-24)

### Bug fixes

Fix a regression introduced in 8.2.0 where static or async class methods with keyword names fail to parse.

## 8.2.0 (2021-04-24)

### New features

Add support for ES2022 class fields and private methods.

## 8.1.1 (2021-04-12)

### Various

Stop shipping source maps in the NPM package.

## 8.1.0 (2021-03-09)

### Bug fixes

Fix a spurious error in nested destructuring arrays.

### New features

Expose `allowAwaitOutsideFunction` in CLI interface.

Make `allowImportExportAnywhere` also apply to `import.meta`.

## 8.0.5 (2021-01-25)

### Bug fixes

Adjust package.json to work with Node 12.16.0 and 13.0-13.6.

## 8.0.4 (2020-10-05)

### Bug fixes

Make `await x ** y` an error, following the spec.

Fix potentially exponential regular expression.

## 8.0.3 (2020-10-02)

### Bug fixes

Fix a wasteful loop during `Parser` creation when setting `ecmaVersion` to `"latest"`.

## 8.0.2 (2020-09-30)

### Bug fixes

Make the TypeScript types reflect the current allowed values for `ecmaVersion`.

Fix another regexp/division tokenizer issue.

## 8.0.1 (2020-08-12)

### Bug fixes

Provide the correct value in the `version` export.

## 8.0.0 (2020-08-12)

### Bug fixes

Disallow expressions like `(a = b) = c`.

Make non-octal escape sequences a syntax error in strict mode.

### New features

The package can now be loaded directly as an ECMAScript module in node 13+.

Update to the set of Unicode properties from ES2021.

### Breaking changes

The `ecmaVersion` option is now required. For the moment, omitting it will still work with a warning, but that will change in a future release.

Some changes to method signatures that may be used by plugins.

## 7.4.0 (2020-08-03)

### New features

Add support for logical assignment operators.

Add support for numeric separators.

## 7.3.1 (2020-06-11)

### Bug fixes

Make the string in the `version` export match the actual library version.

## 7.3.0 (2020-06-11)

### Bug fixes

Fix a bug that caused parsing of object patterns with a property named `set` that had a default value to fail.

### New features

Add support for optional chaining (`?.`).

## 7.2.0 (2020-05-09)

### Bug fixes

Fix precedence issue in parsing of async arrow functions.

### New features

Add support for nullish coalescing.

Add support for `import.meta`.

Support `export * as ...` syntax.

Upgrade to Unicode 13.

## 6.4.1 (2020-03-09)

### Bug fixes

More carefully check for valid UTF16 surrogate pairs in regexp validator.

## 7.1.1 (2020-03-01)

### Bug fixes

Treat `\8` and `\9` as invalid escapes in template strings.

Allow unicode escapes in property names that are keywords.

Don't error on an exponential operator expression as argument to `await`.

More carefully check for valid UTF16 surrogate pairs in regexp validator.

## 7.1.0 (2019-09-24)

### Bug fixes

Disallow trailing object literal commas when ecmaVersion is less than 5.

### New features

Add a static `acorn` property to the `Parser` class that contains the entire module interface, to allow plugins to access the instance of the library that they are acting on.

## 7.0.0 (2019-08-13)

### Breaking changes

Changes the node format for dynamic imports to use the `ImportExpression` node type, as defined in [ESTree](https://github.com/estree/estree/blob/master/es2020.md#importexpression).

Makes 10 (ES2019) the default value for the `ecmaVersion` option.

## 6.3.0 (2019-08-12)

### New features

`sourceType: "module"` can now be used even when `ecmaVersion` is less than 6, to parse module-style code that otherwise conforms to an older standard.

## 6.2.1 (2019-07-21)

### Bug fixes

Fix bug causing Acorn to treat some characters as identifier characters that shouldn't be treated as such.

Fix issue where setting the `allowReserved` option to `"never"` allowed reserved words in some circumstances.

## 6.2.0 (2019-07-04)

### Bug fixes

Improve valid assignment checking in `for`/`in` and `for`/`of` loops.

Disallow binding `let` in patterns.

### New features

Support bigint syntax with `ecmaVersion` >= 11.

Support dynamic `import` syntax with `ecmaVersion` >= 11.

Upgrade to Unicode version 12.

## 6.1.1 (2019-02-27)

### Bug fixes

Fix bug that caused parsing default exports of with names to fail.

## 6.1.0 (2019-02-08)

### Bug fixes

Fix scope checking when redefining a `var` as a lexical binding.

### New features

Split up `parseSubscripts` to use an internal `parseSubscript` method to make it easier to extend with plugins.

## 6.0.7 (2019-02-04)

### Bug fixes

Check that exported bindings are defined.

Don't treat `\u180e` as a whitespace character.

Check for duplicate parameter names in methods.

Don't allow shorthand properties when they are generators or async methods.

Forbid binding `await` in async arrow function's parameter list.

## 6.0.6 (2019-01-30)

### Bug fixes

The content of class declarations and expressions is now always parsed in strict mode.

Don't allow `let` or `const` to bind the variable name `let`.

Treat class declarations as lexical.

Don't allow a generator function declaration as the sole body of an `if` or `else`.

Ignore `"use strict"` when after an empty statement.

Allow string line continuations with special line terminator characters.

Treat `for` bodies as part of the `for` scope when checking for conflicting bindings.

Fix bug with parsing `yield` in a `for` loop initializer.

Implement special cases around scope checking for functions.

## 6.0.5 (2019-01-02)

### Bug fixes

Fix TypeScript type for `Parser.extend` and add `allowAwaitOutsideFunction` to options type.

Don't treat `let` as a keyword when the next token is `{` on the next line.

Fix bug that broke checking for parentheses around an object pattern in a destructuring assignment when `preserveParens` was on.

## 6.0.4 (2018-11-05)

### Bug fixes

Further improvements to tokenizing regular expressions in corner cases.

## 6.0.3 (2018-11-04)

### Bug fixes

Fix bug in tokenizing an expression-less return followed by a function followed by a regular expression.

Remove stray symlink in the package tarball.

## 6.0.2 (2018-09-26)

### Bug fixes

Fix bug where default expressions could fail to parse inside an object destructuring assignment expression.

## 6.0.1 (2018-09-14)

### Bug fixes

Fix wrong value in `version` export.

## 6.0.0 (2018-09-14)

### Bug fixes

Better handle variable-redefinition checks for catch bindings and functions directly under if statements.

Forbid `new.target` in top-level arrow functions.

Fix issue with parsing a regexp after `yield` in some contexts.

### New features

The package now comes with TypeScript definitions.

### Breaking changes

The default value of the `ecmaVersion` option is now 9 (2018).

Plugins work differently, and will have to be rewritten to work with this version.

The loose parser and walker have been moved into separate packages (`acorn-loose` and `acorn-walk`).

## 5.7.3 (2018-09-10)

### Bug fixes

Fix failure to tokenize regexps after expressions like `x.of`.

Better error message for unterminated template literals.

## 5.7.2 (2018-08-24)

### Bug fixes

Properly handle `allowAwaitOutsideFunction` in for statements.

Treat function declarations at the top level of modules like let bindings.

Don't allow async function declarations as the only statement under a label.

## 5.7.0 (2018-06-15)

### New features

Upgraded to Unicode 11.

## 5.6.0 (2018-05-31)

### New features

Allow U+2028 and U+2029 in string when ECMAVersion >= 10.

Allow binding-less catch statements when ECMAVersion >= 10.

Add `allowAwaitOutsideFunction` option for parsing top-level `await`.

## 5.5.3 (2018-03-08)

### Bug fixes

A _second_ republish of the code in 5.5.1, this time with yarn, to hopefully get valid timestamps.

## 5.5.2 (2018-03-08)

### Bug fixes

A republish of the code in 5.5.1 in an attempt to solve an issue with the file timestamps in the npm package being 0.

## 5.5.1 (2018-03-06)

### Bug fixes

Fix misleading error message for octal escapes in template strings.

## 5.5.0 (2018-02-27)

### New features

The identifier character categorization is now based on Unicode version 10.

Acorn will now validate the content of regular expressions, including new ES9 features.

## 5.4.0 (2018-02-01)

### Bug fixes

Disallow duplicate or escaped flags on regular expressions.

Disallow octal escapes in strings in strict mode.

### New features

Add support for async iteration.

Add support for object spread and rest.

## 5.3.0 (2017-12-28)

### Bug fixes

Fix parsing of floating point literals with leading zeroes in loose mode.

Allow duplicate property names in object patterns.

Don't allow static class methods named `prototype`.

Disallow async functions directly under `if` or `else`.

Parse right-hand-side of `for`/`of` as an assignment expression.

Stricter parsing of `for`/`in`.

Don't allow unicode escapes in contextual keywords.

### New features

Parsing class members was factored into smaller methods to allow plugins to hook into it.

## 5.2.1 (2017-10-30)

### Bug fixes

Fix a token context corruption bug.

## 5.2.0 (2017-10-30)

### Bug fixes

Fix token context tracking for `class` and `function` in property-name position.

Make sure `%*` isn't parsed as a valid operator.

Allow shorthand properties `get` and `set` to be followed by default values.

Disallow `super` when not in callee or object position.

### New features

Support [`directive` property](https://github.com/estree/estree/compare/b3de58c9997504d6fba04b72f76e6dd1619ee4eb...1da8e603237144f44710360f8feb7a9977e905e0) on directive expression statements.

## 5.1.2 (2017-09-04)

### Bug fixes

Disable parsing of legacy HTML-style comments in modules.

Fix parsing of async methods whose names are keywords.

## 5.1.1 (2017-07-06)

### Bug fixes

Fix problem with disambiguating regexp and division after a class.

## 5.1.0 (2017-07-05)

### Bug fixes

Fix tokenizing of regexps in an object-desctructuring `for`/`of` loop and after `yield`.

Parse zero-prefixed numbers with non-octal digits as decimal.

Allow object/array patterns in rest parameters.

Don't error when `yield` is used as a property name.

Allow `async` as a shorthand object property.

### New features

Implement the [template literal revision proposal](https://github.com/tc39/proposal-template-literal-revision) for ES9.

## 5.0.3 (2017-04-01)

### Bug fixes

Fix spurious duplicate variable definition errors for named functions.

## 5.0.2 (2017-03-30)

### Bug fixes

A binary operator after a parenthesized arrow expression is no longer incorrectly treated as an error.

## 5.0.0 (2017-03-28)

### Bug fixes

Raise an error for duplicated lexical bindings.

Fix spurious error when an assignement expression occurred after a spread expression.

Accept regular expressions after `of` (in `for`/`of`), `yield` (in a generator), and braced arrow functions.

Allow labels in front or `var` declarations, even in strict mode.

### Breaking changes

Parse declarations following `export default` as declaration nodes, not expressions. This means that class and function declarations nodes can now have `null` as their `id`.

## 4.0.11 (2017-02-07)

### Bug fixes

Allow all forms of member expressions to be parenthesized as lvalue.

## 4.0.10 (2017-02-07)

### Bug fixes

Don't expect semicolons after default-exported functions or classes, even when they are expressions.

Check for use of `'use strict'` directives in non-simple parameter functions, even when already in strict mode.

## 4.0.9 (2017-02-06)

### Bug fixes

Fix incorrect error raised for parenthesized simple assignment targets, so that `(x) = 1` parses again.

## 4.0.8 (2017-02-03)

### Bug fixes

Solve spurious parenthesized pattern errors by temporarily erring on the side of accepting programs that our delayed errors don't handle correctly yet.

## 4.0.7 (2017-02-02)

### Bug fixes

Accept invalidly rejected code like `(x).y = 2` again.

Don't raise an error when a function _inside_ strict code has a non-simple parameter list.

## 4.0.6 (2017-02-02)

### Bug fixes

Fix exponential behavior (manifesting itself as a complete hang for even relatively small source files) introduced by the new 'use strict' check.

## 4.0.5 (2017-02-02)

### Bug fixes

Disallow parenthesized pattern expressions.

Allow keywords as export names.

Don't allow the `async` keyword to be parenthesized.

Properly raise an error when a keyword contains a character escape.

Allow `"use strict"` to appear after other string literal expressions.

Disallow labeled declarations.

## 4.0.4 (2016-12-19)

### Bug fixes

Fix crash when `export` was followed by a keyword that can't be
exported.

## 4.0.3 (2016-08-16)

### Bug fixes

Allow regular function declarations inside single-statement `if` branches in loose mode. Forbid them entirely in strict mode.

Properly parse properties named `async` in ES2017 mode.

Fix bug where reserved words were broken in ES2017 mode.

## 4.0.2 (2016-08-11)

### Bug fixes

Don't ignore period or 'e' characters after octal numbers.

Fix broken parsing for call expressions in default parameter values of arrow functions.

## 4.0.1 (2016-08-08)

### Bug fixes

Fix false positives in duplicated export name errors.

## 4.0.0 (2016-08-07)

### Breaking changes

The default `ecmaVersion` option value is now 7.

A number of internal method signatures changed, so plugins might need to be updated.

### Bug fixes

The parser now raises errors on duplicated export names.

`arguments` and `eval` can now be used in shorthand properties.

Duplicate parameter names in non-simple argument lists now always produce an error.

### New features

The `ecmaVersion` option now also accepts year-style version numbers
(2015, etc).

Support for `async`/`await` syntax when `ecmaVersion` is >= 8.

Support for trailing commas in call expressions when `ecmaVersion` is >= 8.

## 3.3.0 (2016-07-25)

### Bug fixes

Fix bug in tokenizing of regexp operator after a function declaration.

Fix parser crash when parsing an array pattern with a hole.

### New features

Implement check against complex argument lists in functions that enable strict mode in ES7.

## 3.2.0 (2016-06-07)

### Bug fixes

Improve handling of lack of unicode regexp support in host
environment.

Properly reject shorthand properties whose name is a keyword.

### New features

Visitors created with `visit.make` now have their base as _prototype_, rather than copying properties into a fresh object.

## 3.1.0 (2016-04-18)

### Bug fixes

Properly tokenize the division operator directly after a function expression.

Allow trailing comma in destructuring arrays.

## 3.0.4 (2016-02-25)

### Fixes

Allow update expressions as left-hand-side of the ES7 exponential operator.

## 3.0.2 (2016-02-10)

### Fixes

Fix bug that accidentally made `undefined` a reserved word when parsing ES7.

## 3.0.0 (2016-02-10)

### Breaking changes

The default value of the `ecmaVersion` option is now 6 (used to be 5).

Support for comprehension syntax (which was dropped from the draft spec) has been removed.

### Fixes

`let` and `yield` are now “contextual keywords”, meaning you can mostly use them as identifiers in ES5 non-strict code.

A parenthesized class or function expression after `export default` is now parsed correctly.

### New features

When `ecmaVersion` is set to 7, Acorn will parse the exponentiation operator (`**`).

The identifier character ranges are now based on Unicode 8.0.0.

Plugins can now override the `raiseRecoverable` method to override the way non-critical errors are handled.

## 2.7.0 (2016-01-04)

### Fixes

Stop allowing rest parameters in setters.

Disallow `y` rexexp flag in ES5.

Disallow `\00` and `\000` escapes in strict mode.

Raise an error when an import name is a reserved word.

## 2.6.2 (2015-11-10)

### Fixes

Don't crash when no options object is passed.

## 2.6.0 (2015-11-09)

### Fixes

Add `await` as a reserved word in module sources.

Disallow `yield` in a parameter default value for a generator.

Forbid using a comma after a rest pattern in an array destructuring.

### New features

Support parsing stdin in command-line tool.

## 2.5.0 (2015-10-27)

### Fixes

Fix tokenizer support in the command-line tool.

Stop allowing `new.target` outside of functions.

Remove legacy `guard` and `guardedHandler` properties from try nodes.

Stop allowing multiple `__proto__` properties on an object literal in strict mode.

Don't allow rest parameters to be non-identifier patterns.

Check for duplicate paramter names in arrow functions.
