Project: micromark/micromark-extension-mdxjs-esm

Package: micromark-extension-mdxjs-esm@1.0.3

  1. Dependents: 0
  2. micromark extension to support MDX JS import/exports
  1. unified 180
  2. markdown 150
  3. micromark 34
  4. mdx 34
  5. javascript 21
  6. micromark-extension 16
  7. mdxjs 8
  8. ecmascript 6
  9. js 5
  10. export 4
  11. import 2
  12. es 2


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micromark extension to support MDX.js ESM import/exports.

This package provides the low-level modules for integrating with the micromark tokenizer but has no handling of compiling to HTML: go to a syntax tree instead.

When to use this

This package is already included in xdm and mdx-js/mdx (next).

You should probably use micromark-extension-mdx or micromark-extension-mdxjs instead, which combine this package with other MDX features. Alternatively, if you’re using micromark or mdast-util-from-markdown and you don’t want all of MDX, use this package.


This package is ESM only: Node 12+ is needed to use it and it must be imported instead of required.


npm install micromark-extension-mdxjs-esm


import * as acorn from 'acorn'
import {micromark} from 'micromark'
import {mdxjsEsm} from 'micromark-extension-mdxjs-esm'

const output = micromark('import a from "b"\n\n# c', {
  extensions: [mdxjsEsm({acorn})]




…which is rather useless: go to a syntax tree with mdast-util-from-markdown and mdast-util-mdx-expression instead.


This package exports the following identifiers: mdxjsEsm. There is no default export.

The export map supports the endorsed development condition. Run node --conditions development module.js to get instrumented dev code. Without this condition, production code is loaded.


A function that can be called with options that returns an extension for micromark to parse ESM (can be passed in extensions).


Acorn parser to use (Acorn, required).


Options to pass to acorn (Object, default: {ecmaVersion: 2020, locations: true, sourceType: 'module'}). All fields except for locations can be set.


Whether to add an estree field to mdxjsEsm tokens with results from acorn (boolean, default: false).


All valid imports and exports are supported, depending on what the given acorn instance and configuration supports.

When the lowercase strings export or import are found, followed by unicode whitespace (\s), we expect JavaScript. Otherwise, like normal in markdown, we exit and it’ll end up as a paragraph. We continue parsing until we find a line ending followed by a blank line. At that point, we parse with acorn: it if parses, we found our block. Otherwise, if parsing failed at the last character, we assume it’s a blank line in code: we continue on until the next blank line and try again. Otherwise, the acorn error is thrown.

import a from "b"
import * as a from "b"
import {a} from "b"
import {a as b} from "c"
import a, {b as c} from "d"
import a, * as b from "c"
import "a"

export var a = ""
export const a = ""
export let a = ""
export var a, b
export var a = "a", b = "b"
export function a() {}
export class a {}
export var {a} = {}
export var {a: b} = {}
export var [a] = []
export default a = 1
export default function a() {}
export default class a {}
export * from "a"
export * as a from "b"
export {a} from "b"
export {a as b} from "c"
export {default} from "b"
export {default as a, b} from "c"

{/* Blank lines are supported in expressions: */}

export function a() {

  return "b"


{/* A blank line must be used after import/exports: this is incorrect! */}

import a from "b"
## Hello, world!


Could not parse import/exports with acorn: $error

This error occurs if acorn crashes (source: micromark-extension-mdxjs-esm, rule id: acorn). For example:

import 1/1

Unexpected $type in code: only import/exports are supported

This error occurs when a non-ESM construct is found (source: micromark-extension-mdxjs-esm, rule id: non-esm). For example:

export var a = 1
var b


An mdxjsEsm token is used to reflect the block of import/exports in markdown.

It includes:


See contributing.md in micromark/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.


MIT © Titus Wormer