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.

5.7.1 (2018-06-15)

Bug fixes

Make sure the walker and bin files are rebuilt on release (the previous release didn’t get the up-to-date versions).

5.7.0 (2018-06-15)

Bug fixes

Fix crash in walker when walking a binding-less catch node.

New features

Upgraded to Unicode 11.

5.6.2 (2018-06-05)

Bug fixes

In the walker, go back to allowing the baseVisitor argument to be null to default to the default base everywhere.

5.6.1 (2018-06-01)

Bug fixes

Fix regression when passing null as fourth argument to walk.recursive.

5.6.0 (2018-05-31)

Bug fixes

Fix a bug in the walker that caused a crash when walking an object pattern spread.

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 regression in walker causing property values in object patterns to be walked as expressions.

Fix misleading error message for octal escapes in template strings.

5.5.0 (2018-02-27)

Bug fixes

Support object spread in the AST walker.

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.

5.4.1 (2018-02-02)

Bug fixes

5.4.0 somehow accidentally included an old version of walk.js.

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.

The full and fullAncestor walkers no longer visit nodes multiple times.

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.

Make the ES module version of the loose parser actually work.

New features

Implement the template literal revision proposal for ES9.

New walker functions full and fullAncestor.

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 issue with loading acorn_loose.js with an AMD loader.

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.

Don’t crash when the loose parser is called without options object.

New features

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

Make it possible to use visit.ancestor with a walk state.

3.1.0 (2016-04-18)

Bug fixes

Fix issue where the loose parser created invalid TemplateElement nodes for unclosed template literals.

Properly tokenize the division operator directly after a function expression.

Allow trailing comma in destructuring arrays.

New features

The walker now allows defining handlers for CatchClause nodes.

3.0.4 (2016-02-25)


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

3.0.2 (2016-02-10)


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.


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)


Stop allowing rest parameters in setters.

Make sure the loose parser always attaches a local property to ImportNamespaceSpecifier nodes.

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.

2.6.4 (2015-11-12)


Fix crash in loose parser when parsing invalid object pattern.

New features

Support plugins in the loose parser.

2.6.2 (2015-11-10)


Don’t crash when no options object is passed.

2.6.0 (2015-11-09)


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.

2.5.2 (2015-10-27)


Fix bug where the walker walked an exported let statement as an expression.

2.5.0 (2015-10-27)


Fix tokenizer support in the command-line tool.

In the loose parser, don’t allow non-string-literals as import sources.

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.