micromark-extension-mdx-expression

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[micromark][] extension to support [MDX][mdxjs] expressions ({Math.PI}).

* What is this?
* When to use this
* Install
* Use
* API
* mdxExpression(options?)
* Options
* Authoring
* Syntax
* Errors
* Unexpected end of file in expression, expected a corresponding closing brace for {
* Unexpected lazy line in expression in container, expected line to be prefixed…
* Unexpected $type in code: expected an object spread ({...spread})
* Unexpected extra content in spread: only a single spread is supported
* Could not parse expression with acorn
* Tokens
* Types
* Compatibility
* Security
* Related
* Contribute
* License

What is this?

This package contains an extension that adds support for the expression syntax
enabled by [MDX][mdxjs] to [micromark][micromark].
These extensions are used inside MDX.

This package can be made aware or unaware of JavaScript syntax.
When unaware, expressions could include Rust or variables or whatnot.

When to use this

This project is useful when you want to support expressions in markdown.

You can use this extension when you are working with [micromark][micromark].
To support all MDX features, use
[micromark-extension-mdxjs][micromark-extension-mdxjs] instead.

When you need a syntax tree, combine this package with
[mdast-util-mdx-expression][mdast-util-mdx-expression].

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

When you are using [mdx-js/mdx][mdxjs], all of this is already included.

Install

This package is [ESM only][esm].
In Node.js (version 16+), install with [npm][]:

``sh npm install micromark-extension-mdx-expression`

In Deno with [esm.sh][esmsh]:

`js import {mdxExpression} from 'https://esm.sh/micromark-extension-mdx-expression@2'`

In browsers with [esm.sh][esmsh]:

`html`

`Use`

`js import {Parser} from 'acorn' import acornJsx from 'acorn-jsx' import {micromark} from 'micromark' import {mdxExpression} from 'micromark-extension-mdx-expression'

// Unaware of JavaScript (“agnostic”) (balanced braces): const output = micromark('a {1 + 1} b', {extensions: [mdxExpression()]})

console.log(output)

// Aware of JavaScript: micromark('a {!} b', {extensions: [mdxExpression({acorn: Parser.extend(acornJsx())})]})`

Yields:

`html

a b

`text [1:5: Could not parse expression with acorn] { ancestors: undefined, cause: SyntaxError: Unexpected token at pp$4.raise (file:///Users/tilde/Projects/oss/micromark-extension-mdx-expression/node_modules/acorn/dist/acorn.mjs:3547:13) at pp$9.unexpected (file:///Users/tilde/Projects/oss/micromark-extension-mdx-expression/node_modules/acorn/dist/acorn.mjs:758:8) … pos: 4, loc: { line: 1, column: 4 }, raisedAt: 1 }, column: 5, fatal: undefined, line: 1, place: { line: 1, column: 5, offset: 4 }, reason: 'Could not parse expression with acorn', ruleId: 'acorn', source: 'micromark-extension-mdx-expression', url: 'https://github.com/micromark/micromark-extension-mdx-expression/tree/main/packages/micromark-extension-mdx-expression#could-not-parse-expression-with-acorn' }`

…which is useless: go to a syntax tree with [mdast-util-from-markdown][mdast-util-from-markdown] and [mdast-util-mdx-expression][mdast-util-mdx-expression] instead.

`API`

This package exports the identifier [mdxExpression][api-mdx-expression]. There is no default export.

The export map supports the [developmentcondition][development]. Runnode --conditions development module.jsto get instrumented dev code. Without this condition, production code is loaded.

`$3`

Create an extension for micromark to enable MDX expression syntax.

###### Parameters

* options ([Options][api-options], optional) — configuration

###### Returns

Extension for micromark that can be passed in extensionsto enable MDX expression syntax ([Extension][micromark-extension]).

`$3`

Configuration (TypeScript type).

###### Fields

* acorn ([Acorn][acorn], optional) — acorn parser to use *acornOptions ([AcornOptions][acorn-options], default:{ecmaVersion: 2024, locations: true, sourceType: 'module'}) — configuration for acorn; all fields exceptlocationscan be set *addResult (boolean, default: false) — whether to addestree fields to tokens with results from acorn

`Authoring`

When authoring markdown with JavaScript, keep in mind that MDX is a whitespace sensitive and line-based language, while JavaScript is insensitive to whitespace. This affects how markdown and JavaScript interleave with eachother in MDX. For more info on how it works, see [§ Interleaving][mdxjs-interleaving] on the MDX site.

`Syntax`

This extension supports MDX both aware and unaware to JavaScript (respectively gnostic and agnostic). Depending on whether acorn is passed, either valid JavaScript must be used in expressions, or arbitrary text (such as Rust code or so) can be used.

There are two types of expressions: in text (inline, span) or in flow (block). They start with{.

Depending on whether acornis passed, expressions are either parsed in several tries until whole JavaScript is found (as in, nested curly braces depend on JS expression nesting), or they are counted and must be balanced.

Expressions end with }.

For flow (block) expressions, optionally markdown spaces ( or \t) can occur after the closing brace, and finally a markdown line ending (\r, \n) or the end of the file must follow.

While markdown typically knows no errors, for MDX it is decided to instead throw on invalid syntax.

`mdx Here is an expression in a heading:

`Hello, {1 + 1}!`

In agnostic mode, balanced braces can occur: {a + {b} + c}.

In gnostic mode, the value of the expression must be JavaScript, so this would fail: {!}. But, in gnostic mode, braces can be in comments, strings, or in other places: {1 / { / + 2}.

The previous examples were text (inline, span) expressions, they can also be flow (block):

{ 1 + 1 }

This is incorrect, because there are further characters:

{ 1 + 1 }!`

`mdx-invalid Blank lines cannot occur in text, because markdown has already split them in separate constructs, so this is incorrect: {1 +

1}`

`mdx In flow, you can have blank lines:

{ 1 +

2 }`

`Errors`

`$3`

This error occurs if a { was seen without a }(source:micromark-extension-mdx-expression, rule id: unexpected-eof). For example:

`mdx-invalid a { b`

`$3`

This error occurs if a {was seen in a container which then has lazy content (source:micromark-extension-mdx-expression, rule id: unexpected-lazy). For example:

`mdx-invalid > {a b}`

`$3`

This error occurs if a spread was expected but something else was found (source:micromark-extension-mdx-expression, rule id: non-spread). For example:

`mdx-invalid`

`$3`

This error occurs if a spread was expected but more was found after it (source:micromark-extension-mdx-expression, rule id: spread-extra). For example:

`mdx-invalid`

`$3`

This error occurs if acorn crashes or when there is more content after a JS expression (source:micromark-extension-mdx-expression, rule id: acorn). For example:

`mdx-invalid a {"b" "c"} d`

`mdx-invalid a {var b = "c"} d`

`Tokens`

Two tokens are used, mdxFlowExpression and mdxTextExpression, to reflect flow and text expressions.

They include:

* lineEnding for the markdown line endings \r, \n, and \r\n*mdxFlowExpressionMarker and mdxTextExpressionMarkerfor the braces *whitespacefor markdown spaces and tabs in blank lines *mdxFlowExpressionChunk and mdxTextExpressionChunkfor chunks of expression content

`Types`

This package is fully typed with [TypeScript][]. It exports the additional type [Options][api-options].

`Compatibility`

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,micromark-extension-mdx-expression@^2, compatible with Node.js 16.

This package works with micromark version 3 and later.

`Security`

This package is safe.

`Contribute`

See [contributing.md in micromark/.github][contributing] for ways to get started. See [support.md`][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][license] © [Titus Wormer][author]

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

[acorn-options]: https://github.com/acornjs/acorn/blob/96c721dbf89d0ccc3a8c7f39e69ef2a6a3c04dfa/acorn/dist/acorn.d.ts#L16

[api-mdx-expression]: #mdxexpressionoptions

[api-options]: #options

[author]: https://wooorm.com

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

[build]: https://github.com/micromark/micromark-extension-mdx-expression/actions

[build-badge]: https://github.com/micromark/micromark-extension-mdx-expression/workflows/main/badge.svg

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

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

[coc]: https://github.com/micromark/.github/blob/main/code-of-conduct.md

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

[contributing]: https://github.com/micromark/.github/blob/main/contributing.md

[coverage]: https://codecov.io/github/micromark/micromark-extension-mdx-expression

[coverage-badge]: https://img.shields.io/codecov/c/github/micromark/micromark-extension-mdx-expression.svg

[development]: https://nodejs.org/api/packages.html#packages_resolving_user_conditions

[downloads]: https://www.npmjs.com/package/micromark-extension-mdx-expression

[downloads-badge]: https://img.shields.io/npm/dm/micromark-extension-mdx-expression.svg

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

[esmsh]: https://esm.sh

[license]: https://github.com/micromark/micromark-extension-mdx-expression/blob/main/license

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

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

[mdxjs]: https://mdxjs.com

[mdxjs-interleaving]: https://mdxjs.com/docs/what-is-mdx/#interleaving

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

[micromark-extension]: https://github.com/micromark/micromark#syntaxextension

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

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

[remark-mdx]: https://mdxjs.com/packages/remark-mdx/

[size]: https://bundlejs.com/?q=micromark-extension-mdx-expression

[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=micromark-extension-mdx-expression

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

[support]: https://github.com/micromark/.github/blob/main/support.md

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

micromark-extension-mdx-expression

[micromark][] extension to support [MDX][mdxjs] expressions ({Math.PI}).

What is this?

This package contains an extension that adds support for the expression syntax
enabled by [MDX][mdxjs] to [micromark][micromark].
These extensions are used inside MDX.

This package can be made aware or unaware of JavaScript syntax.
When unaware, expressions could include Rust or variables or whatnot.

When to use this

This project is useful when you want to support expressions in markdown.

You can use this extension when you are working with [micromark][micromark].
To support all MDX features, use
[micromark-extension-mdxjs][micromark-extension-mdxjs] instead.

When you need a syntax tree, combine this package with
[mdast-util-mdx-expression][mdast-util-mdx-expression].

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

When you are using [mdx-js/mdx][mdxjs], all of this is already included.

Install

This package is [ESM only][esm].
In Node.js (version 16+), install with [npm][]:

``sh npm install micromark-extension-mdx-expression`

In Deno with [esm.sh][esmsh]:

`js import {mdxExpression} from 'https://esm.sh/micromark-extension-mdx-expression@2'`

In browsers with [esm.sh][esmsh]:

`html`

`Use`

`js import {Parser} from 'acorn' import acornJsx from 'acorn-jsx' import {micromark} from 'micromark' import {mdxExpression} from 'micromark-extension-mdx-expression'

// Unaware of JavaScript (“agnostic”) (balanced braces): const output = micromark('a {1 + 1} b', {extensions: [mdxExpression()]})

console.log(output)

// Aware of JavaScript: micromark('a {!} b', {extensions: [mdxExpression({acorn: Parser.extend(acornJsx())})]})`

Yields:

`html

a b

…which is useless: go to a syntax tree with [mdast-util-from-markdown][mdast-util-from-markdown] and [mdast-util-mdx-expression][mdast-util-mdx-expression] instead.

`API`

This package exports the identifier [mdxExpression][api-mdx-expression]. There is no default export.

The export map supports the [developmentcondition][development]. Runnode --conditions development module.jsto get instrumented dev code. Without this condition, production code is loaded.

`$3`

Create an extension for micromark to enable MDX expression syntax.

###### Parameters

* options ([Options][api-options], optional) — configuration

###### Returns

Extension for micromark that can be passed in extensionsto enable MDX expression syntax ([Extension][micromark-extension]).

`$3`

Configuration (TypeScript type).

###### Fields

`Authoring`

`Syntax`

There are two types of expressions: in text (inline, span) or in flow (block). They start with{.

Expressions end with }.

For flow (block) expressions, optionally markdown spaces ( or \t) can occur after the closing brace, and finally a markdown line ending (\r, \n) or the end of the file must follow.

While markdown typically knows no errors, for MDX it is decided to instead throw on invalid syntax.

`mdx Here is an expression in a heading:

`Hello, {1 + 1}!`

In agnostic mode, balanced braces can occur: {a + {b} + c}.

In gnostic mode, the value of the expression must be JavaScript, so this would fail: {!}. But, in gnostic mode, braces can be in comments, strings, or in other places: {1 / { / + 2}.

The previous examples were text (inline, span) expressions, they can also be flow (block):

{ 1 + 1 }

This is incorrect, because there are further characters:

{ 1 + 1 }!`

`mdx-invalid Blank lines cannot occur in text, because markdown has already split them in separate constructs, so this is incorrect: {1 +

1}`

`mdx In flow, you can have blank lines:

{ 1 +

2 }`

`Errors`

`$3`

This error occurs if a { was seen without a }(source:micromark-extension-mdx-expression, rule id: unexpected-eof). For example:

`mdx-invalid a { b`

`$3`

This error occurs if a {was seen in a container which then has lazy content (source:micromark-extension-mdx-expression, rule id: unexpected-lazy). For example:

`mdx-invalid > {a b}`

`$3`

This error occurs if a spread was expected but something else was found (source:micromark-extension-mdx-expression, rule id: non-spread). For example:

`mdx-invalid`