README
micromark-extension-mdx-expression
micromark extension to support MDX (or MDX.js) expressions.
This package provides the low-level modules for integrating with the micromark tokenizer but has no handling of compiling to HTML: go to a syntax tree instead.
micromark-factory-mdx-expression
and
micromark-util-events-to-acorn
are also maintained here.
When to use this
This package is already included in xdm and mdx-js/mdx
(next).
You should probably use micromark-extension-mdx
or
micromark-extension-mdxjs
instead, which combine this package with
other MDX features.
Alternatively, if you’re using micromark
or
mdast-util-from-markdown
and you don’t want all of MDX, use
this package.
Install
This package is ESM only:
Node 12+ is needed to use it and it must be import
ed instead of require
d.
npm:
npm install micromark-extension-mdx-expression
Use
import * as acorn from 'acorn'
import {micromark} from 'micromark'
import {mdxExpression} from 'micromark-extension-mdx-expression'
// Agnostic (balanced braces):
const output = micromark('a {1 + 1} b', {extensions: [mdxExpression()]})
console.log(output)
// Gnostic (JavaScript):
micromark('a {!} b', {extensions: [mdxExpression({acorn})]})
Yields:
<p>a b</p>
[1:5: Could not parse expression with acorn: Unexpected token] {
reason: 'Could not parse expression with acorn: Unexpected token',
line: 1,
column: 5,
source: 'micromark-extension-mdx-expression',
ruleId: 'acorn',
position: {
start: { line: 1, column: 5, offset: 4 },
end: { line: null, column: null }
}
}
…which is rather useless: go to a syntax tree with
mdast-util-from-markdown
and
mdast-util-mdx-expression
instead.
API
This package exports the following identifiers: mdxExpression
.
There is no default export.
The export map supports the endorsed
development
condition.
Run node --conditions development module.js
to get instrumented dev code.
Without this condition, production code is loaded.
mdxExpression(options?)
A function that can be called with options that returns an extension for
micromark to parse expressions (can be passed in extensions
).
options
options.acorn
Acorn parser to use (Acorn
, optional).
options.acornOptions
Options to pass to acorn (Object
, default: {ecmaVersion: 2020, sourceType: 'module'}
).
All fields can be set.
Positional info (loc
, range
) is set on ES nodes regardless of acorn options.
options.addResult
Whether to add an estree
field to mdxFlowExpression
and mdxTextExpression
tokens with the results from acorn (boolean
, default: false
).
Note that expressions can be empty or be just comments, in which case estree
will be undefined.
Syntax
This extensions support both MDX and MDX.js.
The first is agnostic to the programming language (it could contain Rust or
so), the last is specific to JavaScript.
To turn on gnostic mode, pass acorn
.
There are two types of expressions: in text (inline, span) or in flow (block).
They start with {
.
Depending on whether acorn
is 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.
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
}!
Blank lines cannot occur in text, because markdown has already split them in
separate constructs, so this is incorrect: {1 +
1}
In flow, you can have blank lines:
{
1 +
2
}
Errors
{
Unexpected end of file in expression, expected a corresponding closing brace for This error occurs if a {
was seen without a }
(source:
micromark-extension-mdx-expression
, rule id: unexpected-eof
).
For example:
a { b
Could not parse expression with acorn: Unexpected content after expression
This error occurs when there is more content after a JS expression (source:
micromark-extension-mdx-expression
, rule id: acorn
).
For example:
a {"b" "c"} d
Could not parse expression with acorn: $error
This error occurs if acorn crashes (source: micromark-extension-mdx-expression
,
rule id: acorn
).
For example:
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
andmdxTextExpressionMarker
for the braceswhitespace
for markdown spaces and tabs in blank linesmdxFlowExpressionChunk
andmdxTextExpressionChunk
for chunks of expression content
Related
micromark/micromark
— the smallest commonmark-compliant markdown parser that existsmicromark/micromark-extension-mdx
— micromark extension to support MDXmicromark/micromark-extension-mdxjs
— micromark extension to support MDX.jsmicromark/micromark-extension-mdx-jsx
— micromark extension to support MDX (or MDX.js) JSXmicromark/micromark-extension-mdx-md
— micromark extension to support misc MDX changesmicromark/micromark-extension-mdxjs-esm
— micromark extension to support MDX.js import/exportssyntax-tree/mdast-util-mdx
— mdast utility to support MDX (or MDX.js)
Contribute
See contributing.md
in micromark/.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.