6.4.0 (2019-11-26)

## 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.

# 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` >= 10.

Support dynamic `import` syntax with `ecmaVersion` >= 10.

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 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 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.