babylon

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])

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

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

• 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