Skip to content
A small, fast, JavaScript-based JavaScript parser
JavaScript Other
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.
acorn-loose Mark acorn-loose version 7.0.0 Aug 13, 2019
acorn-walk Update index.js Aug 20, 2019
acorn Mark version 7.1.0 Sep 24, 2019
bin Fix identifier (fixes #846) Jul 20, 2019
.editorconfig Editorconfig: enforce Unix line endings and extra new line in the end… Nov 12, 2014
.gitattributes Force LF endings in code. Jul 29, 2014
.gitignore Replace link script with a static symbolic link Nov 17, 2018
.npmignore build(yarn): Ignore yarn-error.log during publishing Apr 15, 2018
.npmrc Add .npmrc to prevent lockfile from being generated Jun 20, 2019
.tern-project [.tern-project] Load node and es_modules plugins Aug 11, 2015
.travis.yml Update node.js versions in travis Jun 5, 2019
AUTHORS Mark version 7.1.0 Sep 24, 2019 Fix links to license files Jan 31, 2019
logo.svg Fix viewport in logo svg file Sep 6, 2019
package.json Fix wrong field in package.json Jul 20, 2019


Build Status NPM version CDNJS

A tiny, fast JavaScript parser, written completely in JavaScript.


Acorn is open source software released under an MIT license.

You are welcome to report bugs or create pull requests on github. For questions and discussion, please use the Tern discussion forum.


This repository holds three packages:

To build the content of the repository, run npm install.

git clone
cd acorn
npm install

Plugin developments

Acorn is designed to support plugins which can, within reasonable bounds, redefine the way the parser works. Plugins can add new token types and new tokenizer contexts (if necessary), and extend methods in the parser object. This is not a clean, elegant API—using it requires an understanding of Acorn's internals, and plugins are likely to break whenever those internals are significantly changed. But still, it is possible, in this way, to create parsers for JavaScript dialects without forking all of Acorn. And in principle it is even possible to combine such plugins, so that if you have, for example, a plugin for parsing types and a plugin for parsing JSX-style XML literals, you could load them both and parse code with both JSX tags and types.

A plugin is a function from a parser class to an extended parser class. Plugins can be used by simply applying them to the Parser class (or a version of that already extended by another plugin). But because that gets a little awkward, syntactically, when you are using multiple plugins, the static method Parser.extend can be called with any number of plugin values as arguments to create a Parser class extended by all those plugins. You'll usually want to create such an extended class only once, and then repeatedly call parse on it, to avoid needlessly confusing the JavaScript engine's optimizer.

const {Parser} = require("acorn")

const MyParser = Parser.extend(
console.log(MyParser.parse("// Some bigint + JSX code"))

Plugins override methods in their new parser class to implement additional functionality. It is recommended for a plugin package to export its plugin function as its default value or, if it takes configuration parameters, to export a constructor function that creates the plugin function.

This is what a trivial plugin, which adds a bit of code to the readToken method, might look like:

module.exports = function noisyReadToken(Parser) {
  return class extends Parser {
    readToken(code) {
      console.log("Reading a token!")
You can’t perform that action at this time.