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<img alt="babylon" src="https://raw.githubusercontent.com/babel/logo/master/babylon.png" width="700">

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Babylon is a JavaScript parser used in <a href="https://github.com/babel/babel">Babel</a>.

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• 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])

babylon.parseExpression(code, [options])

parse() parses the provided code as an entire ECMAScript program, while parseExpression() tries to parse a single Expression with performance in mind. When in doubt, use .parse().

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.

• startLine: By default, the first line of code parsed is treated as line 1. You can provide a line number to alternatively start with. Useful for integration with other source tools.

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

• strictMode: TODO

Output

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

There is now an estree plugin which reverts these 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

[Babel AST format]: https://github.com/babel/babylon/blob/master/ast/spec.md [ESTree spec]: https://github.com/estree/estree

[Literal]: https://github.com/estree/estree/blob/master/es5.md#literal [Property]: https://github.com/estree/estree/blob/master/es5.md#property [MethodDefinition]: https://github.com/estree/estree/blob/master/es2015.md#methoddefinition

[StringLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#stringliteral [NumericLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#numericliteral [BooleanLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#booleanliteral [NullLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#nullliteral [RegExpLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#regexpliteral [ObjectProperty]: https://github.com/babel/babylon/blob/master/ast/spec.md#objectproperty [ObjectMethod]: https://github.com/babel/babylon/blob/master/ast/spec.md#objectmethod [ClassMethod]: https://github.com/babel/babylon/blob/master/ast/spec.md#classmethod [Program]: https://github.com/babel/babylon/blob/master/ast/spec.md#programs [BlockStatement]: https://github.com/babel/babylon/blob/master/ast/spec.md#blockstatement [Directive]: https://github.com/babel/babylon/blob/master/ast/spec.md#directive [DirectiveLiteral]: https://github.com/babel/babylon/blob/master/ast/spec.md#directiveliteral [FunctionExpression]: https://github.com/babel/babylon/blob/master/ast/spec.md#functionexpression

[Facebook JSX AST]: https://github.com/facebook/jsx/blob/master/AST.md

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

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

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

• 1. Plugins
• estree
• 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
• templateInvalidEscapes