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

6.14.0 (2016-11-16)

:eyeglasses: Spec Compliancy

Throw error for reserved words enum and await (#195) (Kai Cataldo)

11.6.2.2 Future Reserved Words

Babylon will throw for more reserved words such as enum or await (in strict mode).

class enum {} // throws
class await {} // throws in strict mode (module)

Optional names for function types and object type indexers (#197) (Gabe Levi)

So where you used to have to write

type A = (x: string, y: boolean) => number;
type B = (z: string) => number;
type C = { [key: string]: number };

you can now write (with flow 0.34.0)

type A = (string, boolean) => number;
type B = string => number;
type C = { [string]: number };

Parse flow nested array type annotations like number[][] (#219) (Bernhard Häussner)

Supports these form now of specifying array types:

var a: number[][][][];
var b: string[][];

:bug: Bug Fix

Correctly eat semicolon at the end of DelcareModuleExports (#223) (Daniel Tschinder)

declare module "foo" { declare module.exports: number }
declare module "foo" { declare module.exports: number; }  // also allowed now

:house: Internal

• Count Babel tests towards Babylon code coverage (#182) (Moti Zilberman)
• Fix strange line endings (#214) (Thomas Grainger)
• Add node 7 (Daniel Tschinder)
• chore(package): update flow-bin to version 0.34.0 (#204) (Greenkeeper)