micromark-extension-mdxjs-esm

micromark extension to support MDX ESM (import x from 'y').

Contents

• What is this?
• When to use this
• Install
• Use
• API
  • mdxjsEsm(options)
• Authoring
• Syntax
• Errors
  • Could not parse import/exports with acorn: $error
  • Unexpected $type in code: only import/exports are supported
• Tokens
• Types
• Compatibility
• Security
• Related
• Contribute
• License

What is this?

This package contains extensions that add support for ESM enabled by MDX to micromark. It matches how imports and exports work in JavaScript through acorn.

When to use this

These tools are all low-level. In many cases, you want to use remark-mdx with remark instead. When you are using mdx-js/mdx, that is already included.

Even when you want to use micromark, you likely want to use micromark-extension-mdxjs to support all MDX features. That extension includes this extension.

When working with mdast-util-from-markdown, you must combine this package with mdast-util-mdxjs-esm.

Install

This package is ESM only. In Node.js (version 12.20+, 14.14+, 16.0+, or 18.0+), install with npm:

npm install micromark-extension-mdxjs-esm

In Deno with esm.sh:

import {mdxjsEsm} from 'https://esm.sh/micromark-extension-mdxjs-esm@1'

In browsers with esm.sh:

<script type="module">
  import {mdxjsEsm} from 'https://esm.sh/micromark-extension-mdxjs-esm@1?bundle'
</script>

Use

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})]
})

console.log(output)

Yields:

<h1>c</h1>

…which is useless: go to a syntax tree with mdast-util-from-markdown and mdast-util-mdxjs-esm instead.

API

This package exports the identifier 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.

mdxjsEsm(options)

Add support for MDX ESM import/exports.

Function called with options to get a syntax extension for micromark. That extension can be passed in extensions.

options

Configuration (required).

options.acorn

Acorn parser to use (Acorn, required).

options.acornOptions

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

options.addResult

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

Authoring

When authoring markdown with ESM, make sure to follow import and export statements with blank lines before more markdown.

Syntax

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!

Errors

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

Tokens

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

It includes:

• lineEnding for the \r, \n, and \r\n
• lineEndingBlank for the same characters but when after potential whitespace and another line ending
• whitespace for markdown spaces and tabs in blank lines
• mdxjsEsmData for any character in a line of mdxjsEsm

Types

This package is fully typed with TypeScript. It exports the additional type Options.

Compatibility

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, 16.0+, and 18.0+. It also works in Deno and modern browsers.

Security

This package deals with compiling JavaScript. If you do not trust the JavaScript, this package does nothing to change that.

Related

• micromark/micromark-extension-mdxjs — micromark extension to support MDX
• syntax-tree/mdast-util-mdxjs-esm — mdast utility to support MDX ESM
• remark-mdx — remark plugin to support MDX syntax

Contribute

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.

License

MIT © Titus Wormer