# `@mdx-js/mdx`

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MDX compiler.

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## Contents

*   [What is this?](#what-is-this)
*   [When should I use this?](#when-should-i-use-this)
*   [Install](#install)
*   [Use](#use)
*   [API](#api)
    *   [`compile(file, options?)`](#compilefile-options)
    *   [`compileSync(file, options?)`](#compilesyncfile-options)
    *   [`evaluate(file, options)`](#evaluatefile-options)
    *   [`evaluateSync(file, options)`](#evaluatesyncfile-options)
    *   [`run(functionBody, options)`](#runfunctionbody-options)
    *   [`runSync(functionBody, options)`](#runsyncfunctionbody-options)
    *   [`createProcessor(options)`](#createprocessoroptions)
*   [Types](#types)
*   [Architecture](#architecture)
*   [Security](#security)
*   [Contribute](#contribute)
*   [License](#license)

## What is this?

This package is a compiler that turns MDX into JavaScript.
It can also evaluate MDX code.

## When should I use this?

This is the core compiler for turning MDX into JavaScript and which gives you
the most control.
If you’re using a bundler (webpack, Rollup, esbuild), or a site builder (Gatsby,
Next.js) or build system (Vite, WMR) which comes with a bundler, you’re better
off using an integration: see [§ Integrations][integrations].

## Install

This package is [ESM only][esm]:
Node 12+ is needed to use it and it must be `import`ed instead of `require`d.

[npm][]:

```sh
npm install @mdx-js/mdx@next
```

[yarn][]:

```sh
yarn add @mdx-js/mdx@next
```

## Use

Say we have an MDX document, `example.mdx`:

```mdx
export const Thing = () => <>World!</>

# Hello, <Thing />
```

Add some code in `example.js` to compile `example.mdx` to JavaScript:

```js
import {promises as fs} from 'node:fs'
import {compile} from '@mdx-js/mdx'

main()

async function main() {
  const compiled = await compile(await fs.readFile('example.mdx'))
  console.log(String(compiled))
}
```

Yields roughly:

```js
/* @jsxRuntime automatic @jsxImportSource react */
import {Fragment as _Fragment, jsx as _jsx, jsxs as _jsxs} from 'react/jsx-runtime'

export const Thing = () => _jsx(_Fragment, {children: 'World!'})

function MDXContent(props = {}) {
  const {wrapper: MDXLayout} = props.components || ({})
  return MDXLayout
    ? _jsx(MDXLayout, Object.assign({}, props, {children: _jsx(_createMdxContent, {})}))
    : _createMdxContent()
  function _createMdxContent() {
     const _components = Object.assign({h1: 'h1'}, props.components)
     return _jsxs(_components.h1, {children: ['Hello, ', _jsx(Thing, {})]})
   }
}

export default MDXContent
```

See [§ Using MDX][using-mdx] for more on how MDX work and how to use the result.

## API

This package exports the following identifiers:
[`compile`][compile],
[`compileSync`][compile-sync],
[`evaluate`][eval],
[`evaluateSync`](#evaluatesyncfile-options),
[`run`][run],
[`runSync`](#runsyncfunctionbody-options), and
[`createProcessor`][create-processor].
There is no default export.

### `compile(file, options?)`

Compile MDX to JS.

###### `file`

MDX document to parse (`string`, [`Buffer`][buffer] in UTF-8, [`vfile`][vfile],
or anything that can be given to `vfile`).

<details>
<summary>Example</summary>

```js
import {VFile} from 'vfile'
import {compile} from '@mdx-js/mdx'

await compile(':)')
await compile(Buffer.from(':-)'))
await compile({path: 'path/to/file.mdx', value: '🥳'})
await compile(new VFile({path: 'path/to/file.mdx', value: '🤭'}))
```

</details>

###### `options.remarkPlugins`

List of [remark plugins][remark-plugins], presets, and pairs.

<details>
<summary>Example</summary>

```js
import remarkFrontmatter from 'remark-frontmatter' // YAML and such.
import remarkGfm from 'remark-gfm' // Tables, footnotes, strikethrough, task lists, literal URLs.

await compile(file, {remarkPlugins: [remarkGfm]}) // One plugin.
await compile(file, {remarkPlugins: [[remarkFrontmatter, 'toml']]}) // A plugin with options.
await compile(file, {remarkPlugins: [remarkGfm, remarkFrontmatter]}) // Two plugins.
await compile(file, {remarkPlugins: [[remarkGfm, {singleTilde: false}], remarkFrontmatter]}) // Two plugins, first w/ options.
```

</details>

###### `options.rehypePlugins`

List of [rehype plugins][rehype-plugins], presets, and pairs.

<details>
<summary>Example</summary>

```js
import rehypeKatex from 'rehype-katex' // Render math with KaTeX.
import remarkMath from 'remark-math' // Support math like `$so$`.

await compile(file, {remarkPlugins: [remarkMath], rehypePlugins: [rehypeKatex]})

await compile(file, {
  remarkPlugins: [remarkMath],
  // A plugin with options:
  rehypePlugins: [[rehypeKatex, {throwOnError: true, strict: true}]]
})
```

</details>

###### `options.recmaPlugins`

List of recma plugins.
This is a new ecosystem, currently in beta, to transform [esast][] trees
(JavaScript).

###### `options.mdExtensions`

List of markdown extensions, with dot (`Array<string>`, default: `['.md',
'.markdown', '.mdown', '.mkdn', '.mkd', '.mdwn', '.mkdown', '.ron']`).

###### `options.mdxExtensions`

List of MDX extensions, with dot (`Array<string>`, default: `['.mdx']`).
Has no effect in `compile` or `evaluate` but does affect
[§ Integrations][integrations].

###### `options.format`

Format the file is in (`'detect' | 'mdx' | 'md'`, default: `'detect'`).

*   `'detect'` — use `'markdown'` for files with an extension in `mdExtensions`
    and `'mdx'` otherwise
*   `'mdx'` — treat file as [MDX][mdx-syntax]
*   `'md'` — treat file as plain vanilla markdown

The format cannot be detected if a file is passed without a path or extension:
`mdx` will be assumed.
So pass a full vfile (with `path`) or an object with a path.

<details>
<summary>Example</summary>

```js
compile({value: '…'}) // Seen as MDX
compile({value: '…'}, {format: 'md'}) // Seen as markdown
compile({value: '…', path: 'readme.md'}) // Seen as markdown

// Please do not use `.md` for MDX as other tools won’t know how to handle it.
compile({value: '…', path: 'readme.md'}, {format: 'mdx'}) // Seen as MDX
compile({value: '…', path: 'readme.md'}, {mdExtensions: []}) // Seen as MDX
```

</details>

This option mostly affects [§ Integrations][integrations]
because in those it affects *which* files are “registered”:

*   `format: 'mdx'` registers the extensions in `options.mdxExtensions`
*   `format: 'md'` registers the extensions in `options.mdExtensions`
*   `format: 'detect'` registers both lists of extensions

###### `options.outputFormat`

Output format to generate (`'program' | 'function-body'`, default: `'program'`).
In most cases `'program'` should be used, as it results in a whole program.
Internally, [`evaluate`][eval] uses `outputFormat: 'function-body'` to compile
to code that can be `eval`ed with [`run`][run].
In some cases, you might want to do what `evaluate` does in separate steps
yourself, such as when compiling on the server and running on the client.

The `'program'` format will use import statements to import the runtime (and
optionally provider) and use an export statement to yield the `MDXContent`
component.

The `'function-body'` format will get the runtime (and optionally provider) from
`arguments[0]`, rewrite export statements, and use a return statement to yield
what was exported.
Normally, this output format will throw on `import` (and `export … from`)
statements, but you can support them by setting
[`options.useDynamicImport`][usedynamicimport].

<details>
<summary>Example</summary>

A module `example.js`:

```js
import {compile} from '@mdx-js/mdx'

main('export const no = 3.14\n\n# hi {no}')

async function main(code) {
  console.log(String(await compile(code, {outputFormat: 'program'}))) // Default
  console.log(String(await compile(code, {outputFormat: 'function-body'})))
}
```

…yields:

```js
import {Fragment as _Fragment, jsx as _jsx} from 'react/jsx-runtime'
export const no = 3.14
function MDXContent(props = {}) { /* … */ }
export default MDXContent
```

```js
const {Fragment: _Fragment, jsx: _jsx} = arguments[0]
const no = 3.14
function MDXContent(props = {}) { /* … */ }
return {no, default: MDXContent}
```

</details>

###### `options.useDynamicImport`

Whether to compile to dynamic import expressions (`boolean`, default: `false`).
This option applies when [`options.outputFormat`][outputformat] is
`'function-body'`.

`@mdx-js/mdx` can turn import statements (`import x from 'y'`) into dynamic
imports (`const {x} = await import('y')`).
This is useful because import statements only work at the top level of
JavaScript modules, whereas `import()` is available inside function bodies.

When you turn `useDynamicImport` on, you should probably set [`options.baseUrl`][baseurl] too.

<details>
<summary>Example</summary>

Say we have a couple modules:

```js
// meta.js:
export const title = 'World'

// numbers.js:
export const no = 3.14

// example.js:
import {compileSync} from '@mdx-js/mdx'

const code = `import {name} from './meta.js'
export {no} from './numbers.js'

# hi {name}!`

console.log(String(compileSync(code, {outputFormat: 'function-body', useDynamicImport: true})))
```

…now running `node example.js` yields:

```js
const {Fragment: _Fragment, jsx: _jsx, jsxs: _jsxs} = arguments[0]
const {name} = await import('./meta.js')
const {no} = await import('./numbers.js')
function MDXContent(props = {}) { /* … */ }
return {no, default: MDXContent}
```

</details>

###### `options.baseUrl`

Resolve relative `import` (and `export … from`) from this URL (`string?`,
example: `import.meta.url`).

Relative specifiers are non-absolute URLs that start with `/`, `./`, or `../`.
For example: `/index.js`, `./folder/file.js`, or `../main.js`.

This option is useful when code will run in a different place.
One example is when `.mdx` files are in path *a* but compiled to path *b* and
imports should run relative the path *b*.
Another example is when evaluating code, whether in Node or a browser.

<details>
<summary>Example</summary>

Say we have a module `example.js`:

```js
import {compile} from '@mdx-js/mdx'

main()

async function main() {
  const code = 'export {number} from "./data.js"\n\n# hi'
  const baseUrl = 'https://a.full/url' // Typically `import.meta.url`
  console.log(String(await compile(code, {baseUrl})))
}
```

…now running `node example.js` yields:

```js
import {Fragment as _Fragment, jsx as _jsx} from 'react/jsx-runtime'
export {number} from 'https://a.full/data.js'
function MDXContent(props = {}) { /* … */ }
export default MDXContent
```

</details>

###### `options.development`

Whether to add extra information to error messages in generated code
(`boolean?`, default: `false`).
The default can be set to `true` in Node.js through environment variables: set
`NODE_ENV=development`.

<details>
<summary>Example</summary>

Say we had some MDX that references a component that can be passed or provided
at runtime:

```mdx
**Note**<NoteIcon />: some stuff.
```

And a module to evaluate that:

```js
import {promises as fs} from 'node:fs'
import * as runtime from 'react/jsx-runtime'
import {evaluate} from '@mdx-js/mdx'

main()

async function main() {
  const path = 'example.mdx'
  const value = await fs.readFile(path)
  const MDXContent = (await evaluate({path, value}, runtime)).default
  console.log(MDXContent())
}
```

Running that would normally (production) yield:

```txt
Error: Expected component `NoteIcon` to be defined: you likely forgot to import, pass, or provide it.
    at _missingMdxReference (eval at run (…/@mdx-js/mdx/lib/run.js:18:10), <anonymous>:27:9)
    at _createMdxContent (eval at run (…/@mdx-js/mdx/lib/run.js:18:10), <anonymous>:15:20)
    at MDXContent (eval at run (…/@mdx-js/mdx/lib/run.js:18:10), <anonymous>:9:9)
    at main (…/example.js:11:15)
```

But if we change add `development: true` to our example:

```diff
@@ -7,6 +7,6 @@ main()
 async function main() {
   const path = 'example.mdx'
   const value = await fs.readFile(path)
-  const MDXContent = (await evaluate({path, value}, runtime)).default
+  const MDXContent = (await evaluate({path, value}, {development: true, ...runtime})).default
   console.log(MDXContent({}))
 }
```

And we’d run it again, we’d get:

```txt
Error: Expected component `NoteIcon` to be defined: you likely forgot to import, pass, or provide it.
It’s referenced in your code at `1:9-1:21` in `example.mdx`
provide it.
    at _missingMdxReference (eval at run (…/@mdx-js/mdx/lib/run.js:18:10), <anonymous>:27:9)
    at _createMdxContent (eval at run (…/@mdx-js/mdx/lib/run.js:18:10), <anonymous>:15:20)
    at MDXContent (eval at run (…/@mdx-js/mdx/lib/run.js:18:10), <anonymous>:9:9)
    at main (…/example.js:11:15)
```

</details>

###### `options.SourceMapGenerator`

The `SourceMapGenerator` class from [`source-map`][source-map] (optional).
When given, the resulting file will have a `map` field set to a source map (in
object form).

<details>
<summary>Example</summary>

Assuming `example.mdx` from [§ Use][use] exists, then:

```js
import {promises as fs} from 'node:fs'
import {SourceMapGenerator} from 'source-map'
import {compile} from '@mdx-js/mdx'

main()

async function main() {
  const file = await compile(
    {path: 'example.mdx', value: await fs.readFile('example.mdx')},
    {SourceMapGenerator}
  )

  console.log(file.map)
}
```

…yields:

```js
{
  version: 3,
  sources: ['example.mdx'],
  names: ['Thing'],
  mappings: ';;aAAaA,QAAQ;YAAQ;;;;;;;;iBAE3B',
  file: 'example.mdx'
}
```

</details>

###### `options.providerImportSource`

Place to import a provider from (`string?`, example: `'@mdx-js/react'`).
Useful for runtimes that support context (React, Preact).
The provider must export a `useMDXComponents`, which is called to access an
object of components.

<details>
<summary>Example</summary>

If `file` is the contents of `example.mdx` from [§ Use][use], then:

```js
compile(file, {providerImportSource: '@mdx-js/react'})
```

…yields this difference:

```diff
 /* @jsxRuntime automatic @jsxImportSource react */
 import {Fragment as _Fragment, jsx as _jsx, jsxs as _jsxs} from 'react/jsx-runtime'
+import {useMDXComponents as _provideComponents} from '@mdx-js/react'

 export const Thing = () => _jsx(_Fragment, {children: 'World!'})

 function MDXContent(props = {}) {
-  const {wrapper: MDXLayout} = props.components || ({})
+  const {wrapper: MDXLayout} = Object.assign({}, _provideComponents(), props.components)
   return MDXLayout
     ? _jsx(MDXLayout, Object.assign({}, props, {children: _jsx(_createMdxContent, {})}))
     : _createMdxContent()
   function _createMdxContent() {
-    const _components = Object.assign({h1: 'h1'}, props.components)
+    const _components = Object.assign({h1: 'h1'}, _provideComponents(), props.components)
     return _jsxs(_components.h1, {children: ['Hello, ', _jsx(Thing, {})]})
   }
 }

 export default MDXContent
```

</details>

###### `options.jsx`

Whether to keep JSX (`boolean?`, default: `false`).
The default is to compile JSX away so that the resulting file is immediately
runnable.

<details>
<summary>Example</summary>

If `file` is the contents of `example.mdx` from [§ Use][use], then:

```js
compile(file, {jsx: true})
```

…yields this difference:

```diff
 /* @jsxRuntime automatic @jsxImportSource react */
-import {Fragment as _Fragment, jsx as _jsx, jsxs as _jsxs} from 'react/jsx-runtime'

-export const Thing = () => _jsx(_Fragment, {children: 'World!'})
+export const Thing = () => <>World!</>

 function MDXContent(props = {}) {
   const {wrapper: MDXLayout} = props.components || ({})
   return MDXLayout
-    ? _jsx(MDXLayout, Object.assign({}, props, {children: _jsx(_createMdxContent, {})}))
+    ? <MDXLayout {...props}><_createMdxContent /></MDXLayout>
     : _createMdxContent()
   function _createMdxContent() {
     const _components = Object.assign({h1: 'h1'}, props.components)
-    return _jsxs(_components.h1, {children: ['Hello, ', _jsx(Thing, {})]})
+    return <_components.h1>{"Hello, "}<Thing /></_components.h1>
   }
 }

 export default MDXContent
```

</details>

###### `options.jsxRuntime`

JSX runtime to use (`'automatic' | 'classic'`, default: `'automatic'`).
The classic runtime compiles to calls such as `h('p')`, the automatic runtime
compiles to `import _jsx from '$importSource/jsx-runtime'\n_jsx('p')`.

<details>
<summary>Example</summary>

If `file` is the contents of `example.mdx` from [§ Use][use], then:

```js
compile(file, {jsxRuntime: 'classic'})
```

…yields this difference:

```diff
-/* @jsxRuntime automatic @jsxImportSource react */
-import {Fragment as _Fragment, jsx as _jsx, jsxs as _jsxs} from 'react/jsx-runtime'
+/* @jsxRuntime classic @jsx React.createElement @jsxFrag React.Fragment */
+import React from 'react'

-export const Thing = () => _jsx(_Fragment, {children: 'World!'})
+export const Thing = () => React.createElement(React.Fragment, null, 'World!')
…
```

</details>

###### `options.jsxImportSource`

Place to import automatic JSX runtimes from (`string?`, default: `'react'`).
When in the `automatic` runtime, this is used to define an import for
`_Fragment`, `_jsx`, and `_jsxs`.

<details>
<summary>Example</summary>

If `file` is the contents of `example.mdx` from [§ Use][use], then:

```js
compile(file, {jsxImportSource: 'preact'})
```

…yields this difference:

```diff
-/* @jsxRuntime automatic @jsxImportSource react */
-import {Fragment as _Fragment, jsx as _jsx, jsxs as _jsxs} from 'react/jsx-runtime'
+/* @jsxRuntime automatic @jsxImportSource preact */
+import {Fragment as _Fragment, jsx as _jsx, jsxs as _jsxs } from 'preact/jsx-runtime'
```

</details>

###### `options.pragma`

Pragma for JSX (`string?`, default: `'React.createElement'`).
When in the `classic` runtime, this is used as an identifier for function calls:
`<x />` to `React.createElement('x')`.

You should most probably define `pragmaFrag` and `pragmaImportSource` too when
changing this.

<details>
<summary>Example</summary>

If `file` is the contents of `example.mdx` from [§ Use][use], then:

```js
compile(file, {
  jsxRuntime: 'classic',
  pragma: 'preact.createElement',
  pragmaFrag: 'preact.Fragment',
  pragmaImportSource: 'preact/compat'
})
```

…yields this difference:

```diff
-/* @jsxRuntime classic @jsx React.createElement @jsxFrag React.Fragment */
-import React from 'react'
+/* @jsxRuntime classic @jsx preact.createElement @jsxFrag preact.Fragment */
+import preact from 'preact/compat'

-export const Thing = () => React.createElement(React.Fragment, null, 'World!')
+export const Thing = () => preact.createElement(preact.Fragment, null, 'World!')
…
```

</details>

###### `options.pragmaFrag`

Pragma for JSX fragments (`string?`, default: `'React.Fragment'`).
When in the `classic` runtime, this is used as an identifier for fragments: `<>`
to `React.createElement(React.Fragment)`.

See `options.pragma` for an example.

###### `options.pragmaImportSource`

Where to import the identifier of `pragma` from (`string?`, default: `'react'`).
When in the `classic` runtime, this is used to import the `pragma` function.
To illustrate with an example: when `pragma` is `'a.b'` and `pragmaImportSource`
is `'c'` this following will be generated: `import a from 'c'`.

See `options.pragma` for an example.

###### Returns

`Promise<VFile>` — Promise that resolves to the compiled JS as a [vfile][].

<details>
<summary>Example</summary>

```js
import remarkPresetLintConsistent from 'remark-preset-lint-consistent' // Lint rules to check for consistent markdown.
import {reporter} from 'vfile-reporter'
import {compile} from '@mdx-js/mdx'

main()

async function main() {
  const file = await compile('*like this* or _like this_?', {remarkPlugins: [remarkPresetLintConsistent]})
  console.error(reporter(file))
}
```

Yields:

```txt
  1:16-1:27  warning  Emphasis should use `*` as a marker  emphasis-marker  remark-lint

⚠ 1 warning
```

</details>

### `compileSync(file, options?)`

Compile MDX to JS.
Synchronous version of `compile`.
When possible please use the async `compile`.

### `evaluate(file, options)`

> ☢️ **Danger**: It’s called **evaluate** because it `eval`s JavaScript.

[Compile][] and [run][] MDX.
When possible, please use `compile`, write to a file, and then run with Node,
or use one of the
[§ Integrations][integrations].
But if you trust your content, `evaluate` can work.

Typically, `import` (or `export … from`) do not work here.
They can be compiled to dynamic `import()` by passing
[`options.useDynamicImport`][usedynamicimport].

###### `file`

See [`compile`][compile].

###### `options`

Most options are the same as [`compile`][compile], with the following
exceptions:

*   `providerImportSource` is replaced by `useMDXComponents`
*   `jsx*` and `pragma*` options are replaced by `jsx`, `jsxs`, and `Fragment`
*   `outputFormat` is set to `function-body`

###### `options.jsx`

###### `options.jsxs`

###### `options.Fragment`

These three options are required.
They come from an automatic JSX runtime that you must import yourself.

<details>
<summary>Example</summary>

```js
import * as runtime from 'react/jsx-runtime'

const {default: Content} = await evaluate('# hi', {...runtime, ...otherOptions})
```

</details>

###### `options.useMDXComponents`

Needed if you want to support a provider.

<details>
<summary>Example</summary>

```js
import * as provider from '@mdx-js/react'
import * as runtime from 'react/jsx-runtime'

const {default: Content} = await evaluate('# hi', {...provider, ...runtime, ...otherOptions})
```

</details>

###### Returns

`Promise<OMDXModule>` — Promise that resolves to something that looks a bit like
a module: an object with a `default` field set to the component and anything
else that was exported from the MDX file available too.

<details>
<summary>Example</summary>

Assuming the contents of `example.mdx` from [§ Use][use] was in `file`, then:

```js
import * as runtime from 'react/jsx-runtime'
import {evaluate} from '@mdx-js/mdx'

console.log(await evaluate(file, {...runtime}))
```

…yields:

```js
{Thing: [Function: Thing], default: [Function: MDXContent]}
```

</details>

###### Note: Performance

Compiling (and running) MDX takes time.
If you’re live-rendering a string of MDX that often changes using a virtual DOM
based framework (such as React), one performance improvement is to call the
`MDXContent` component yourself.
The reason is that the `evaluate` creates a new function each time, which cannot
be diffed:

```diff
 const {default: MDXContent} = await evaluate('…')

-<MDXContent {...props} />
+MDXContent(props)
```

### `evaluateSync(file, options)`

> ☢️ **Danger**: It’s called **evaluate** because it `eval`s JavaScript.

Compile and run MDX.
Synchronous version of [`evaluate`][eval].
When possible please use the async `evaluate`.

### `run(functionBody, options)`

> ☢️ **Danger**: This `eval`s JavaScript.

Run MDX compiled as [`options.outputFormat: 'function-body'`][outputformat].

###### `options`

You can pass `jsx`, `jsxs`, and `Fragment` from an automatic JSX runtime as
`options`.
You can also pass `useMDXComponents` from a provider in options if the MDX is
compiled with `options.providerImportSource: '#'` (the exact value of this
compile option doesn’t matter).
All other options have to be passed to `compile` instead.

###### Returns

`Promise<MDXModule>` — See `evaluate`

<details>
<summary>Example</summary>

On the server:

```js
import {compile} from '@mdx-js/mdx'

const code = String(await compile('# hi', {outputFormat: 'function-body'}))
// To do: send `code` to the client somehow.
```

On the client:

```js
import * as runtime from 'react/jsx-runtime'
import {run} from '@mdx-js/mdx'

const code = '' // To do: get `code` from server somehow.

const {default: Content} = await run(code, runtime)
```

…yields:

```js
[Function: MDXContent]
```

</details>

### `runSync(functionBody, options)`

> ☢️ **Danger**: This `eval`s JavaScript.

Run MDX.
Synchronous version of [`run`][run].
When possible please use the async `run`.

### `createProcessor(options)`

Create a unified processor to compile MDX to JS.
Has the same options as [`compile`][compile], but returns a configured
[`processor`][processor].

Note that `format: 'detect'` does not work here: only `'md'` or `'mdx'` are
allowed (and `'mdx'` is the default).

## Types

This package is fully typed with [TypeScript][].
See [§ Types][types] on our website for information.

Additional `CompileOptions`, `EvaluateOptions`, and `ProcessorOptions` types
are exported, which represents acceptable configuration for their respective
methods.

## Architecture

To understand what this project does, it’s very important to first understand
what unified does: please read through the [`unifiedjs/unified`][unified] readme
(the part until you hit the API section is required reading).

`@mdx-js/mdx` is a unified pipeline — wrapped so that most folks don’t need to
know about unified: [`core.js#L65`][core].
The processor goes through these steps:

1.  Parse MDX (serialized markdown with embedded JSX, ESM, and expressions)
    to mdast (markdown syntax tree)
2.  Transform through remark (markdown ecosystem)
3.  Transform mdast to hast (HTML syntax tree)
4.  Transform through rehype (HTML ecosystem)
5.  Transform hast to esast (JS syntax tree)
6.  Do the work needed to get a component
7.  Transform through recma (JS ecosystem)
8.  Serialize esast as JavaScript

The *input* is MDX (serialized markdown with embedded JSX, ESM, and
expressions).
The markdown is parsed with [`micromark/micromark`][micromark] and the embedded
JS with one of its extensions
[`micromark/micromark-extension-mdxjs`][micromark-extension-mdxjs] (which in
turn uses [acorn][]).
Then [`syntax-tree/mdast-util-from-markdown`][mdast-util-from-markdown] and its
extension [`syntax-tree/mdast-util-mdx`][mdast-util-mdx] are used to turn the
results from the parser into a syntax tree: [mdast][].

Markdown is closest to the source format.
This is where [remark plugins][remark-plugins] come in.
Typically, there shouldn’t be much going on here.
But perhaps you want to support GFM (tables and such) or frontmatter?
Then you can add a plugin here: `remark-gfm` or `remark-frontmatter`,
respectively.

After markdown, we go to [hast][] (HTML).
This transformation is done by
[`syntax-tree/mdast-util-to-hast`][mdast-util-to-hast].
Wait, why, what does HTML have to do with it?
Part of the reason is that we care about HTML semantics: we want to know that
something is an `<a>`, not whether it’s a link with a resource (`[text](url)`)
or a reference to a defined link definition (`[text][id]\n\n[id]: url`).
So an HTML AST is *closer* to where we want to go.
Another reason is that there are many things folks need when they go MDX -> JS,
markdown -> HTML, or even folks who only process their HTML -> HTML: use cases
other than MDX.
By having a single AST in these cases and writing a plugin that works on that
AST, that plugin can supports *all* these use cases (for example,
[`rehypejs/rehype-highlight`][rehype-highlight] for syntax highlighting or
[`rehypejs/rehype-katex`][rehype-katex] for math).
So, this is where [rehype plugins][rehype-plugins] come in: most of the plugins,
probably.

Then we go to JavaScript: [esast][] (JS; an
AST which is compatible with estree but looks a bit more like other unist ASTs).
This transformation is done by
[`syntax-tree/hast-util-to-estree`][hast-util-to-estree].
This is a new ecosystem that does not have utilities or plugins yet.
But it’s where `@mdx-js/mdx` does its thing: where it adds imports/exports,
where it compiles JSX away into `_jsx()` calls, and where it does the other cool
things that it provides.

Finally, The output is serialized JavaScript.
That final step is done by [astring][], a
small and fast JS generator.

## Security

See [§ Security][security] on our website for information.

## Contribute

See [§ Contribute][contribute] on our website for ways to get started.
See [§ Support][support] for ways to get help.

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

## License

[MIT][] © Compositor and [Vercel][]

[build-badge]: https://github.com/mdx-js/mdx/workflows/main/badge.svg

[build]: https://github.com/mdx-js/mdx/actions

[coverage-badge]: https://img.shields.io/codecov/c/github/mdx-js/mdx/main.svg

[coverage]: https://codecov.io/github/mdx-js/mdx

[downloads-badge]: https://img.shields.io/npm/dm/@mdx-js/mdx.svg

[downloads]: https://www.npmjs.com/package/@mdx-js/mdx

[size-badge]: https://img.shields.io/bundlephobia/minzip/@mdx-js/mdx.svg

[size]: https://bundlephobia.com/result?p=@mdx-js/mdx

[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg

[backers-badge]: https://opencollective.com/unified/backers/badge.svg

[collective]: https://opencollective.com/unified

[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg

[chat]: https://github.com/mdx-js/mdx/discussions

[npm]: https://docs.npmjs.com/cli/install

[yarn]: https://classic.yarnpkg.com/docs/cli/add/

[contribute]: https://mdxjs.com/community/contribute/

[support]: https://mdxjs.com/community/support/

[coc]: https://github.com/mdx-js/.github/blob/HEAD/code-of-conduct.md

[mit]: https://github.com/mdx-js/mdx/blob/main/packages/mdx/license

[vercel]: https://vercel.com

[compile]: #compilefile-options

[compile-sync]: #compilesyncfile-options

[eval]: #evaluatefile-options

[run]: #runfunctionbody-options

[create-processor]: #createprocessoroptions

[buffer]: https://nodejs.org/api/buffer.html

[source-map]: https://github.com/mozilla/source-map

[vfile]: https://github.com/vfile/vfile

[remark-plugins]: https://github.com/remarkjs/remark/blob/main/doc/plugins.md#list-of-plugins

[rehype-plugins]: https://github.com/rehypejs/rehype/blob/main/doc/plugins.md#list-of-plugins

[mdx-syntax]: https://mdxjs.com/mdx/#mdx-syntax

[use]: #use

[outputformat]: #optionsoutputformat

[baseurl]: #optionsbaseurl

[usedynamicimport]: #optionsusedynamicimport

[unified]: https://github.com/unifiedjs/unified

[processor]: https://github.com/unifiedjs/unified#processor

[core]: https://github.com/mdx-js/mdx/blob/main/packages/mdx/lib/core.js#L65

[micromark]: https://github.com/micromark/micromark

[acorn]: https://github.com/acornjs/acorn

[micromark-extension-mdxjs]: https://github.com/micromark/micromark-extension-mdxjs

[mdast-util-from-markdown]: https://github.com/syntax-tree/mdast-util-from-markdown

[mdast-util-mdx]: https://github.com/syntax-tree/mdast-util-mdx

[mdast]: https://github.com/syntax-tree/mdast

[mdast-util-to-hast]: https://github.com/syntax-tree/mdast-util-to-hast

[hast]: https://github.com/syntax-tree/hast

[hast-util-to-estree]: https://github.com/syntax-tree/hast-util-to-estree

[rehype-highlight]: https://github.com/rehypejs/rehype-highlight

[rehype-katex]: https://github.com/remarkjs/remark-math/tree/main/packages/rehype-katex

[esast]: https://github.com/syntax-tree/esast

[astring]: https://github.com/davidbonnet/astring

[integrations]: https://mdxjs.com/getting-started/#integrations

[using-mdx]: https://mdxjs.com/using-mdx/

[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[types]: https://mdxjs.com/getting-started/#types

[security]: https://mdxjs.com/getting-started/#security

[typescript]: https://www.typescriptlang.org
