https://github.com/acornjs/acorn

A small, fast, JavaScript-based JavaScript parser
https://github.com/acornjs/acorn

Last synced: 6 days ago
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A small, fast, JavaScript-based JavaScript parser

• Host: GitHub
• URL: https://github.com/acornjs/acorn
• Owner: acornjs
• Created: 2012-09-24T10:05:00.000Z (over 12 years ago)
• Default Branch: master
• Last Pushed: 2024-12-29T21:28:56.000Z (20 days ago)
• Last Synced: 2025-01-06T12:22:20.386Z (13 days ago)
• Language: JavaScript
• Homepage:
• Size: 5.91 MB
• Stars: 10,712
• Watchers: 177
• Forks: 896
• Open Issues: 13
• Metadata Files:
  • Readme: README.md
  • Authors: AUTHORS

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README

        
# Acorn

[![Build Status](https://github.com/acornjs/acorn/workflows/ci/badge.svg)](https://github.com/acornjs/acorn/actions)

[![NPM version](https://img.shields.io/npm/v/acorn.svg)](https://www.npmjs.com/package/acorn)

[![CDNJS](https://img.shields.io/cdnjs/v/acorn.svg)](https://cdnjs.com/libraries/acorn)  

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

## Community



Acorn is open source software released under an

[MIT license](https://github.com/acornjs/acorn/blob/master/acorn/LICENSE).

You are welcome to

[report bugs](https://github.com/acornjs/acorn/issues) or create pull

requests on [github](https://github.com/acornjs/acorn).

## Packages

This repository holds three packages:

 - [acorn](https://github.com/acornjs/acorn/tree/master/acorn/): The

   main parser

 - [acorn-loose](https://github.com/acornjs/acorn/tree/master/acorn-loose/): The

   error-tolerant parser

 - [acorn-walk](https://github.com/acornjs/acorn/tree/master/acorn-walk/): The

   syntax tree walker

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

```sh

git clone https://github.com/acornjs/acorn.git

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.

```javascript

const {Parser} = require("acorn")

const MyParser = Parser.extend(

  require("acorn-jsx")(),

  require("acorn-bigint")

)

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:

```javascript

module.exports = function noisyReadToken(Parser) {

  return class extends Parser {

    readToken(code) {

      console.log("Reading a token!")

      super.readToken(code)

    }

  }

}

```