babylon

Babylon is a JavaScript parser used in Babel.

• The latest ECMAScript version enabled by default (ES2017).
• Comment attachment.
• Support for JSX and Flow.
• Support for experimental language proposals (accepting PRs for anything at least stage-0.

Credits

Heavily based on acorn and acorn-jsx, thanks to the awesome work of @RReverser and @marijnh.

Significant diversions are expected to occur in the future such as streaming, EBNF definitions, sweet.js integration, interspatial parsing and more.

API

babylon.parse(code, [options])

Options

• allowImportExportEverywhere: By default, import and export declarations can only appear at a program's top level. Setting this option to true allows them anywhere where a statement is allowed.

• allowReturnOutsideFunction: By default, a return statement at the top level raises an error. Set this to true to accept such code.

• allowSuperOutsideMethod TODO

• sourceType: Indicate the mode the code should be parsed in. Can be either "script" or "module".

• sourceFilename: Correlate output AST nodes with their source filename. Useful when generating code and source maps from the ASTs of multiple input files.

• plugins: Array containing the plugins that you want to enable.

Output

Babylon generates AST according to Babel AST format. It is based on ESTree spec with the following deviations:

• Literal token is replaced with StringLiteral, NumericLiteral, BooleanLiteral, NullLiteral, RegExpLiteral
• Property token is replaced with ObjectProperty and ObjectMethod
• MethodDefinition is replaced with ClassMethod
• Program and BlockStatement contain additional directives field with Directive and DirectiveLiteral
• ClassMethod, ObjectProperty, and ObjectMethod value property's properties in FunctionExpression is coerced/brought into the main method node.

AST for JSX code is based on Facebook JSX AST with the addition of one node type:

• JSXText

Semver

Babylon follows semver in most situations. The only thing to note is that some spec-compliancy bug fixes may be released under patch versions.

For example: We push a fix to early error on something like #107 - multiple default exports per file. That would be considered a bug fix even though it would cause a build to fail.

Example

require("babylon").parse("code", {
  // parse in strict mode and allow module declarations
  sourceType: "module",

  plugins: [
    // enable jsx and flow syntax
    "jsx",
    "flow"
  ]
});

Plugins

• jsx
• flow
• doExpressions
• objectRestSpread
• decorators
• classProperties
• exportExtensions
• asyncGenerators
• functionBind
• functionSent
• dynamicImport

Changelog

v6.13.0 (2016-10-21)

:eyeglasses: Spec Compliancy

Property variance type annotations for Flow plugin (#161) (Sam Goldman)

See https://flowtype.org/docs/variance.html for more information

type T = { +p: T };
interface T { -p: T };
declare class T { +[k:K]: V };
class T { -[k:K]: V };
class C2 { +p: T = e };

Raise error on duplicate definition of proto (#183) (Moti Zilberman)

({ __proto__: 1, __proto__: 2 }) // Throws an error now

:bug: Bug Fix

Flow: Allow class properties to be named static (#184) (Moti Zilberman)

declare class A {
  static: T;
}

Allow "async" as identifier for object literal property shorthand (#187) (Andrew Levine)

var foo = { async, bar };

:nail_care: Polish

Fix flowtype and add inType to state (#189) (Daniel Tschinder)

This improves the performance slightly (because of hidden classes)

:house: Internal

Fix .gitattributes line ending setting (#191) (Moti Zilberman)

Increase test coverage (#175 (Moti Zilberman)

Readd missin .eslinignore for IDEs (Daniel Tschinder)

Error on missing expected.json fixture in CI (#188) (Moti Zilberman)

Add .gitattributes and .editorconfig for LF line endings (#179) (Moti Zilberman)

Fixes two tests that are failing after the merge of #172 (#177) (Moti Zilberman)