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 (Based on an outdated version of the Decorators proposal. Will be removed in a future version of Babylon)
• classProperties
• exportExtensions
• asyncGenerators
• functionBind
• functionSent
• dynamicImport

Changelog

6.15.0 (2017-01-10)

:eyeglasses: Spec Compliancy

Add support for Flow shorthand import type (#267) (Jeff Morrison)

This change implements flows new shorthand import syntax and where previously you had to write this code:

import {someValue} from "blah";
import type {someType} from "blah";
import typeof {someOtherValue} from "blah";

you can now write it like this:

import {
  someValue,
  type someType,
  typeof someOtherValue,
} from "blah";

For more information look at this pull request.

flow: allow leading pipes in all positions (#256) (Vladimir Kurchatkin)

This change now allows a leading pipe everywhere types can be used:

var f = (x): | 1 | 2 => 1;

Throw error when exporting non-declaration (#241) (Kai Cataldo)

Previously babylon parsed the following exports, although they are not valid:

export typeof foo;
export new Foo();
export function() {};
export for (;;);
export while(foo);

:bug: Bug Fix

Don't set inType flag when parsing property names (#266) (Vladimir Kurchatkin)

This fixes parsing of this case:

const map = {
  [age <= 17] : 'Too young'
};

Fix source location for JSXEmptyExpression nodes (fixes #248) (#249) (James Long)

The following case produced an invalid AST

<div>{/* foo */}</div>

Use fromCodePoint to convert high value unicode entities (#243) (Ryan Duffy)

When high value unicode entities (e.g. 💩) were used in the input source code they are now correctly encoded in the resulting AST.

Rename folder to avoid Windows-illegal characters (#281) (Ryan Plant)

Allow this.state.clone() when parsing decorators (#262) (Alex Rattray)

:house: Internal

User external-helpers (#254) (Daniel Tschinder)

Add watch script for dev (#234) (Kai Cataldo)

Freeze current plugins list for "*" option, and remove from README.md (#245) (Andrew Levine)

Prepare tests for multiple fixture runners. (#240) (Daniel Tschinder)

Add some test coverage for decorators stage-0 plugin (#250) (Andrew Levine)

Refactor tokenizer types file (#263) (Sven SAULEAU)

Update eslint-config-babel to the latest version 🚀 (#273) (greenkeeper[bot])

chore(package): update rollup to version 0.41.0 (#272) (greenkeeper[bot])

chore(package): update flow-bin to version 0.37.0 (#255) (greenkeeper[bot])