Babylon is a JavaScript parser used in Babel.

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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.


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().



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

AST for JSX code is based on Facebook JSX AST with the addition of one node type:


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.


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

  plugins: [
    // enable jsx and flow syntax