mdast extensions to parse and serialize MDX expressions.

• What is this?
• When to use this
• Install
• Use
• API
  • mdxExpressionFromMarkdown
  • mdxExpressionToMarkdown
• Syntax tree
  • Nodes
  • Content model
• Types
• Compatibility
• Related
• Contribute
• License

This package contains extensions that add support for the expression syntax enabled by MDX to mdast-util-from-markdown and mdast-util-to-markdown.

These tools are all rather low-level. In most cases, you’d want to use remark-mdx with remark instead.

When you are working with syntax trees and want all of MDX, use mdast-util-mdx instead.

When working with mdast-util-from-markdown, you must combine this package with micromark-extension-mdx-expression.

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

npm install mdast-util-mdx-expression

In Deno with esm.sh:

import {mdxExpressionFromMarkdown, mdxExpressionToMarkdown} from 'https://esm.sh/mdast-util-mdx-expression@1'

In browsers with esm.sh:

<script type="module">
  import {mdxExpressionFromMarkdown, mdxExpressionToMarkdown} from 'https://esm.sh/mdast-util-mdx-expression@1?bundle'
</script>

Say our document example.mdx contains:

{
  a + 1
}

b {true}.

…and our module example.js looks as follows:

import fs from 'node:fs/promises'
import * as acorn from 'acorn'
import {fromMarkdown} from 'mdast-util-from-markdown'
import {toMarkdown} from 'mdast-util-to-markdown'
import {mdxExpression} from 'micromark-extension-mdx-expression'
import {mdxExpressionFromMarkdown, mdxExpressionToMarkdown} from 'mdast-util-mdx-expression'

const doc = await fs.readFile('example.mdx')

const tree = fromMarkdown(doc, {
  extensions: [mdxExpression({acorn, addResult: true})],
  mdastExtensions: [mdxExpressionFromMarkdown]
})

console.log(tree)

const out = toMarkdown(tree, {extensions: [mdxExpressionToMarkdown]})

console.log(out)

…now running node example.js yields (positional info removed for brevity):

{
  type: 'root',
  children: [
    {
      type: 'mdxFlowExpression',
      value: '\na + 1\n',
      data: {
        estree: {
          type: 'Program',
          body: [
            {
              type: 'ExpressionStatement',
              expression: {
                type: 'BinaryExpression',
                left: {type: 'Identifier', name: 'a'},
                operator: '+',
                right: {type: 'Literal', value: 1, raw: '1'}
              }
            }
          ],
          sourceType: 'module'
        }
      }
    },
    {
      type: 'paragraph',
      children: [
        {type: 'text', value: 'b '},
        {
          type: 'mdxTextExpression',
          value: 'true',
          data: {
            estree: {
              type: 'Program',
              body: [
                {
                  type: 'ExpressionStatement',
                  expression: {type: 'Literal', value: true, raw: 'true'}
                }
              ],
              sourceType: 'module'
            }
          }
        },
        {type: 'text', value: '.'}
      ]
    }
  ]
}

{
  a + 1
}

b {true}.

This package exports the identifiers mdxExpressionFromMarkdown and mdxExpressionToMarkdown. There is no default export.

Extension for mdast-util-from-markdown.

When using the syntax extension with addResult, nodes will have a data.estree field set to an ESTree.

Extension for mdast-util-to-markdown.

The following interfaces are added to mdast by this utility.

interface MDXFlowExpression <: Literal {
  type: "mdxFlowExpression"
}

MDXFlowExpression (Literal) represents a JavaScript expression embedded in flow (block). It can be used where flow content is expected. Its content is represented by its value field.

For example, the following markdown:

{
  1 + 1
}

Yields:

{type: 'mdxFlowExpression', value: '\n1 + 1\n'}

interface MDXTextExpression <: Literal {
  type: "mdxTextExpression"
}

MDXTextExpression (Literal) represents a JavaScript expression embedded in text (span, inline). It can be used where phrasing content is expected. Its content is represented by its value field.

For example, the following markdown:

a {1 + 1} b.

Yields:

{type: 'mdxTextExpression', value: '1 + 1'}

type FlowContentMdxExpression = MDXFlowExpression | FlowContent

type PhrasingContentMdxExpression = MDXTextExpression | PhrasingContent

This package is fully typed with TypeScript. It exports the additional types MdxFlowExpression and MdxTextExpression.

It also registers the node types with @types/mdast. If you’re working with the syntax tree, make sure to import this utility somewhere in your types, as that registers the new node types in the tree.

/**
 * @typedef {import('mdast-util-mdx-expression')}
 */

import {visit} from 'unist-util-visit'

/** @type {import('mdast').Root} */
const tree = getMdastNodeSomeHow()

visit(tree, (node) => {
  // `node` can now be an expression node.
})

Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, and 16.0+. Our projects sometimes work with older versions, but this is not guaranteed.

This plugin works with mdast-util-from-markdown version 1+ and mdast-util-to-markdown version 1+.

• remarkjs/remark-mdx — remark plugin to support MDX
• syntax-tree/mdast-util-mdx — mdast utility to support MDX
• micromark/micromark-extension-mdx-expression — micromark extension to parse MDX expressions

See contributing.md in syntax-tree/.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