mdast extensions to parse and serialize MDX expressions ({Math.PI}).

• What is this?
• When to use this
• Install
• Use
• API
  • mdxExpressionFromMarkdown()
  • mdxExpressionToMarkdown()
  • MdxFlowExpression
  • MdxTextExpression
  • MdxFlowExpressionHast
  • MdxTextExpressionHast
• HTML
• Syntax
• Syntax tree
  • Nodes
  • Content model
• Types
• Compatibility
• Related
• Contribute
• License

This package contains two extensions that add support for MDX expression syntax in markdown to mdast. These extensions plug into mdast-util-from-markdown (to support parsing expressions in markdown into a syntax tree) and mdast-util-to-markdown (to support serializing expressions in syntax trees to markdown).

You can use these extensions when you are working with mdast-util-from-markdown and mdast-util-to-markdown already.

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

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

All these packages are used in remark-mdx, which focusses on making it easier to transform content by abstracting these internals away.

This package is ESM only. In Node.js (version 16+), 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@2'

In browsers with esm.sh:

<script type="module">
  import {mdxExpressionFromMarkdown, mdxExpressionToMarkdown} from 'https://esm.sh/mdast-util-mdx-expression@2?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 {mdxExpression} from 'micromark-extension-mdx-expression'
import {fromMarkdown} from 'mdast-util-from-markdown'
import {mdxExpressionFromMarkdown, mdxExpressionToMarkdown} from 'mdast-util-mdx-expression'
import {toMarkdown} from 'mdast-util-to-markdown'

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.

Create an extension for mdast-util-from-markdown to enable MDX expressions in markdown.

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

Extension for mdast-util-from-markdown to enable MDX expressions (FromMarkdownExtension).

Create an extension for mdast-util-to-markdown to enable MDX expressions in markdown.

Extension for mdast-util-to-markdown to enable MDX expressions (ToMarkdownExtension).

MDX expression node, occurring in flow (block) (TypeScript type).

import type {Program} from 'estree-jsx'
import type {Data, Literal} from 'mdast'

interface MdxFlowExpression extends Literal {
  type: 'mdxFlowExpression'
  data?: MdxFlowExpressionData | undefined
}

interface MdxFlowExpressionData extends Data {
  estree?: Program | null | undefined
}

MDX expression node, occurring in text (block) (TypeScript type).

import type {Program} from 'estree-jsx'
import type {Data, Literal} from 'mdast'

interface MdxTextExpression extends Literal {
  type: 'mdxTextExpression'
  data?: MdxTextExpressionData | undefined
}

interface MdxTextExpressionData extends Data {
  estree?: Program | null | undefined
}

Same as MdxFlowExpression, but registered with @types/hast (TypeScript type).

import type {Program} from 'estree-jsx'
import type {Data, Literal} from 'hast'

interface MdxFlowExpressionHast extends Literal {
  type: 'mdxFlowExpression'
  data?: MdxFlowExpressionData | undefined
}

interface MdxFlowExpressionData extends Data {
  estree?: Program | null | undefined
}

Same as MdxTextExpression, but registered with @types/hast (TypeScript type).

import type {Program} from 'estree-jsx'
import type {Data, Literal} from 'hast'

interface MdxTextExpressionHast extends Literal {
  type: 'mdxTextExpression'
  data?: MdxTextExpressionData | undefined
}

interface MdxTextExpressionData extends Data {
  estree?: Program | null | undefined
}

MDX expressions have no representation in HTML. Though, when you are dealing with MDX, you will likely go through hast. You can enable passing MDX expressions through to hast by configuring mdast-util-to-hast with passThrough: ['mdxFlowExpression', 'mdxTextExpression'].

See Syntax in micromark-extension-mdx-expression.

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, MdxFlowExpressionHast, MdxTextExpression, and MdxTextExpressionHast.

It also registers the node types with @types/mdast and @types/hast. 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.

/**
 * @import {} from 'mdast-util-mdx-expression'
 * @import {Root} from 'mdast'
 */

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

/** @type {Root} */
const tree = getMdastNodeSomeHow()

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

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, mdast-util-mdx-expression@^2, compatible with Node.js 16.

This utility works with mdast-util-from-markdown version 2+ and mdast-util-to-markdown version 2+.

• remark-mdx — remark plugin to support MDX
• mdast-util-mdx — mdast utility to support MDX
• 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