acorn-jsx

What is acorn-jsx?

The acorn-jsx npm package is a plugin for the Acorn JavaScript parser that allows it to parse JSX syntax. JSX is a syntax extension for JavaScript commonly used with React to describe what the UI should look like. By using acorn-jsx, developers can extend the Acorn parser to handle JSX elements as part of the JavaScript code, enabling the development of tools like linters, code formatters, and compilers that work with JSX.

What are acorn-jsx's main functionalities?

JSX Parsing

This feature allows the parsing of JSX syntax by extending the Acorn parser. The code sample demonstrates how to create a new parser instance that can parse a string containing JSX code and output the abstract syntax tree (AST).

const acorn = require('acorn');
const jsx = require('acorn-jsx');
const JSXParser = acorn.Parser.extend(jsx());
const code = `<div>Hello, world!</div>`;
const ast = JSXParser.parse(code, {ecmaVersion: 2020});
console.log(ast);

Other packages similar to acorn-jsx

espree

Espree is an actively maintained ECMAScript parser built on top of Acorn by the ESLint team. It is designed to be compatible with Esprima and is used primarily for the ESLint project. Espree supports JSX out of the box and is a good alternative to acorn-jsx for projects that require compatibility with ESLint's use cases.

esprima

Esprima is a high performance, standard-compliant ECMAScript parser that also supports JSX. It is often used for static analysis tools and source code transformation. While Esprima and acorn-jsx both support JSX, Esprima is a standalone parser, whereas acorn-jsx is a plugin that extends Acorn.

README

Acorn-JSX

This is plugin for Acorn - a tiny, fast JavaScript parser, written completely in JavaScript.

It was created as an experimental alternative, faster React.js JSX parser.

According to benchmarks, Acorn-JSX is 2x faster than official Esprima-based parser when location tracking is turned on in both (call it "source maps enabled mode"). At the same time, it consumes all the ES6+JSX syntax that can be consumed by Esprima-FB (this is proved by official tests).

UPDATE [14-Apr-2015]: Facebook implementation started deprecation process in favor of Acorn + Acorn-JSX + Babel for parsing and transpiling JSX syntax.

Transpiler

Please note that this tool only parses source code to JSX AST, which is useful for various language tools and services. If you want to transpile your code to regular ES5-compliant JavaScript with source map, check out the babel transpiler which uses acorn-jsx under the hood.

Usage

You can use module directly in order to get Acorn instance with plugin installed:

var acorn = require('acorn-jsx');

Or you can use inject.js for injecting plugin into your own version of Acorn like following:

var acorn = require('acorn-jsx/inject')(require('./custom-acorn'));

Then, use plugins option whenever you need to support JSX while parsing:

var ast = acorn.parse(code, {
  plugins: { jsx: true }
});

Note that official spec doesn't support mix of XML namespaces and object-style access in tag names (#27) like in <namespace:Object.Property />, so it was deprecated in acorn-jsx@3.0. If you still want to opt-in to support of such constructions, you can pass the following option:

var ast = acorn.parse(code, {
  plugins: {
    jsx: { allowNamespacedObjects: true }
  }
});

Also, since most apps use pure React transformer, a new option was introduced that allows to prohibit namespaces completely:

var ast = acorn.parse(code, {
  plugins: {
    jsx: { allowNamespaces: false }
  }
});

Note that by default allowNamespaces is enabled for spec compliancy.

License

This plugin is issued under the MIT license.