MDX


AST

This document defines two syntax trees:

  • MDXAST, a superset of mdast, to represent markdown with embedded JSX
  • MDXHAST, a superset of hast, to represent HTML with embedded JSX

MDXAST

The majority of the MDXAST specification is defined by mdast. MDXAST is a superset with the following additional node types:

  • jsx (instead of html)
  • comment (instead of html comments)
  • import
  • export

It’s important to note that any MDX document without those nodes is valid mdast.

Differences to mdast

The import type is used to provide the necessary block elements to the remark HTML block parser and for the execution context/implementation. For example, a webpack loader might want to transform an MDX import by appending those imports.

An export is used to emit data from MDX, similarly to traditional markdown frontmatter.

The jsx node would most likely be passed to Babel to create functions.

This will also differ a bit in parsing because the remark parser is built to handle particular HTML element types, whereas JSX support will require the ability to parse any tag, and those that self close.

The jsx, comment, import, and export node types are defined below.

Nodes

JSX

interface JSX <: Literal {
  type: "jsx"
}

JSX (Literal) represents embedded JSX.

For example, the following MDX:

<Heading hi='there'>
  Hello, world!
</Heading>

Yields:

{
  "type": "jsx",
  "value": "<Heading hi='there'>
  Hello, world!
</Heading>"
}

Comment

interface Comment <: Literal {
  type: "comment"
}

Comment (Literal) represents an embedded comment.

For example, the following MDX:

<!--hidden-->

Yields:

{
  "type": "comment",
  "value": "<!--hidden-->"
}

Import

interface Import <: Literal {
  type: "import"
}

Import (Literal) represents an ECMAScript import statement.

For example, the following MDX:

import Video from '../components/Video'

Yields:

{
  "type": "import",
  "value": "import Video from '../components/Video'"
}

Export

interface Export <: Literal {
  type: "import"
  default: boolean?
}

Export (Literal) represents an ECMAScript export statement.

An default field can be present. It represents that the export statement is a default export (when true) or not (when false or not present).

For example, the following MDX:

export { foo: 'bar' }

Yields:

{
  "type": "export",
  "default": false,
  "value": "export { foo: 'bar' }"
}

MDXHAST

The majority of the MDXHAST specification is defined by hast. MDXHAST includes all nodes defined by MDXAST, except for Comment, as it’s defined by hast already.