The Babel parser (previously Babylon) is a JavaScript parser used in Babel.

  • The latest ECMAScript version enabled by default (ES2017).
  • Comment attachment.
  • Support for JSX, Flow, Typescript.
  • Support for experimental language proposals (accepting PRs for anything at least stage-0).


Heavily based on acorn and acorn-jsx, thanks to the awesome work of @RReverser and @marijnh.


babelParser.parse(code, [options])

babelParser.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().


  • 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.
  • allowAwaitOutsideFunction: By default, await use is not allowed outside of an async function. Set this to true to accept such code.
  • allowReturnOutsideFunction: By default, a return statement at the top level raises an error. Set this to true to accept such code.
  • allowSuperOutsideMethod: By default, super use is not allowed outside of class and object methods. Set this to true to accept such code.
  • sourceType: Indicate the mode the code should be parsed in. Can be one of "script", "module", or "unambiguous". Defaults to "script". "unambiguous" will make @babel/parser attempt to guess, based on the presence of ES6 import or export statements. Files with ES6 imports and exports are considered "module" and are otherwise "script".
  • 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: By default, ECMAScript code is parsed as strict only if a "use strict"; directive is present or if the parsed file is an ECMAScript module. Set this option to true to always parse files in strict mode.
  • ranges: Adds a ranges property to each node: [node.start, node.end]
  • tokens: Adds all parsed tokens to a tokens property on the File node

Js中文网 – 前端进阶资源教程 ,Babel中文文档


The Babel parser 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.


The Babel Parser 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("@babel/parser").parse("code", {
  // parse in strict mode and allow module declarations
  sourceType: "module",

  plugins: [
    // enable jsx and flow syntax




Code Example

estree (repo)


Language extensions


Code Example

flow (repo)

var a: string = "";

flowComments (docs)

/:: type Foo = {...}; /

jsx (repo)

<a attr="b">{s}</a>

typescript (repo)

var a: string = "";

ECMAScript proposals


Code Example

asyncGenerators (proposal)

async function*() {}, for await (let a of b) {}

bigInt (proposal)


classProperties (proposal)

class A { b = 1; }

classPrivateProperties (proposal)

class A { #b = 1; }

classPrivateMethods (proposal)

class A { #c() {} }

decorators (proposal)

@a class A {}

doExpressions (proposal)

var a = do { if (true) { 'hi'; } };

dynamicImport (proposal)


exportDefaultFrom (proposal)

export v from "mod"

exportNamespaceFrom (proposal)

export * as ns from "mod"

functionBind (proposal)

a::b, ::console.log



importMeta (proposal)


logicalAssignment (proposal)

a &&= b

nullishCoalescingOperator (proposal)

a ?? b

numericSeparator (proposal)


objectRestSpread (proposal)

var a = { b, ...c };

optionalCatchBinding (proposal)

try {throw 0;} catch{do();}

optionalChaining (proposal)


partialApplication (proposal)

f(?, a)

pipelineOperator (proposal)

a |> b

throwExpressions (proposal)

() => throw new Error("")

Plugins options

NOTE: When a plugin is specified multiple times, only the first options are considered.

  • decorators:

    • decoratorsBeforeExport (boolean)
        // decoratorsBeforeExport: true
        export class C {}

        // decoratorsBeforeExport: false
        export @dec class C {}
  • pipelineOperator:

  • flow:

    • all (boolean, default: false) Some code has different meaning in Flow and in vanilla JavaScript. For example, foo<T>(x) is parsed as a call expression with a type argument in Flow, but as a comparison (foo < T > x) accordingly to the ECMAScript specification. By default, babel-parser parses those ambiguous constructs as Flow types only if the file starts with a // @flow pragma. Set this option to true to always parse files as if // @flow was specified.


Will the Babel parser support a plugin system?

Previous issues: #1351, #6694.

We currently aren’t willing to commit to supporting the API for plugins or the resulting ecosystem (there is already enough work maintaining Babel’s own plugin system). It’s not clear how to make that API effective, and it would limit our ability to refactor and optimize the codebase.

Our current recommendation for those that want to create their own custom syntax is for users to fork the parser.

To consume your custom parser, you can add a plugin to your options to call the parser via its npm package name or require it if using JavaScript,

const parse = require("custom-fork-of-babel-parser-on-npm-here");

module.exports = {
  plugins: [{
    parserOverride(code, opts) {
      return parse(code, opts);

← typescriptcore →

来源:Js中文网 – 前端进阶资源教程



  1. 关注我们的 GitHub 博客,让我们成为长期关系
  2. 把这篇文章分享给你的朋友 / 交流群,让更多的人看到,一起进步,一起成长!
  3. 关注公众号 「IT平头哥联盟」,公众号后台回复「资源」 免费领取我精心整理的前端进阶资源教程

JS中文网是中国领先的新一代开发者社区和专业的技术媒体,一个帮助开发者成长的社区,目前已经覆盖和服务了超过 300 万开发者,你每天都可以在这里找到技术世界的头条内容。欢迎热爱技术的你一起加入交流与学习,JS中文网的使命是帮助开发者用代码改变世界