README.md



  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