unified lets you inspect and transform content with plugins.
Contents
What is this?
unified is two things:
- unified is a collective of 500+ free and open source packages that work
with content as structured data (ASTs)
unified (this project) is the core package, used in 1.3m+ projects on GH,
to process content with plugins
Several ecosystems are built on unified around different kinds of content.
Notably, remark (markdown), rehype (HTML), and retext (natural
language).
These ecosystems can be connected together.
When should I use this?
In some cases, you are already using unified.
For example, it’s used in MDX, Gatsby, Docusaurus, etc.
In those cases, you don’t need to add unified yourself but you can include
plugins into those projects.
But the real fun (for some) is to get your hands dirty and work with syntax
trees and build with it yourself.
You can create those projects, or things like Prettier, or your own site
generator.
You can connect utilities together and make your own plugins that check for
problems and transform from one thing to another.
When you are dealing with one type of content (such as markdown), you can use
the main package of that ecosystem instead (so remark).
When you are dealing with different kinds of content (such as markdown and
HTML), it’s recommended to use unified itself, and pick and choose the plugins
you need.
Install
This package is ESM only.
In Node.js (version 16+), install with npm:
npm install unified
In Deno with esm.sh:
import {unified} from 'https://esm.sh/unified@11'
In browsers with esm.sh:
<script type="module">
import {unified} from 'https://esm.sh/unified@11?bundle'
</script>
Use
import rehypeDocument from 'rehype-document'
import rehypeFormat from 'rehype-format'
import rehypeStringify from 'rehype-stringify'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import {unified} from 'unified'
import {reporter} from 'vfile-reporter'
const file = await unified()
.use(remarkParse)
.use(remarkRehype)
.use(rehypeDocument, {title: '👋🌍'})
.use(rehypeFormat)
.use(rehypeStringify)
.process('# Hello world!')
console.error(reporter(file))
console.log(String(file))
Yields:
no issues found
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>👋🌍</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Hello world!</h1>
</body>
</html>
Overview
unified is an interface for processing content with syntax trees.
Syntax trees are a representation of content understandable to programs.
Those programs, called plugins, take these trees and inspect and
modify them.
To get to the syntax tree from text, there is a parser.
To get from that back to text, there is a compiler.
This is the process of a processor.
| ........................ process ........................... |
| .......... parse ... | ... run ... | ... stringify ..........|
+--------+ +----------+
Input ->- | Parser | ->- Syntax Tree ->- | Compiler | ->- Output
+--------+ | +----------+
X
|
+--------------+
| Transformers |
+--------------+
Processors
Processors process content.
On its own, unified (the root processor) doesn’t work.
It needs to be configured with plugins to work.
For example:
const processor = unified()
.use(remarkParse)
.use(remarkRehype)
.use(rehypeDocument, {title: '👋🌍'})
.use(rehypeFormat)
.use(rehypeStringify)
That processor can do different things.
It can:
- …parse markdown (
parse)
- …turn parsed markdown into HTML and format the HTML (
run)
- …compile HTML (
stringify)
- …do all of the above (
process)
Every processor implements another processor.
To create a processor, call another processor.
The new processor is configured to work the same as its ancestor.
But when the descendant processor is configured in the future it does not affect
the ancestral processor.
When processors are exposed from a module (for example, unified itself) they
should not be configured directly, as that would change their behavior for all
module users.
Those processors are frozen and they should be called to create
a new processor before they are used.
File
When processing a document, metadata is gathered about that document.
vfile is the file format that stores data, metadata, and messages
about files for unified and plugins.
There are several utilities for working with these files.
Syntax tree
The syntax trees used in unified are unist nodes.
A tree represents a whole document and each node is a plain JavaScript
object with a type field.
The semantics of nodes and the format of syntax trees is defined by other
projects:
There are many utilities for working with trees listed in each aforementioned
project and maintained in the syntax-tree organization.
These utilities are a level lower than unified itself and are building blocks
that can be used to make plugins.
Ecosystems
Around each syntax tree is an ecosystem that focusses on that particular kind
of content.
At their core, they parse text to a tree and compile that tree back to text.
They also provide plugins that work with the syntax tree, without requiring
that the end user has knowledge about that tree.
Plugins
Each aforementioned ecosystem comes with a large set of plugins that you can
pick and choose from to do all kinds of things.
There are also a few plugins that work in any ecosystem:
Configuration
Processors are configured with plugins or with the
data method.
Most plugins also accept configuration through options.
See each plugin’s readme for more info.
Integrations
unified can integrate with the file system through
unified-engine.
CLI apps can be created with unified-args, Gulp plugins with
unified-engine-gulp, and language servers with
unified-language-server.
A streaming interface can be created with unified-stream.
Programming interface
The API provided by unified allows multiple files to be processed and
gives access to metadata (such as lint messages):
import rehypeStringify from 'rehype-stringify'
import remarkParse from 'remark-parse'
import remarkPresetLintMarkdownStyleGuide from 'remark-preset-lint-markdown-style-guide'
import remarkRehype from 'remark-rehype'
import remarkRetext from 'remark-retext'
import retextEnglish from 'retext-english'
import retextEquality from 'retext-equality'
import {unified} from 'unified'
import {reporter} from 'vfile-reporter'
const file = await unified()
.use(remarkParse)
.use(remarkPresetLintMarkdownStyleGuide)
.use(remarkRetext, unified().use(retextEnglish).use(retextEquality))
.use(remarkRehype)
.use(rehypeStringify)
.process('*Emphasis* and _stress_, you guys!')
console.error(reporter(file))
console.log(String(file))
Yields:
1:16-1:24 warning Emphasis should use `*` as a marker emphasis-marker remark-lint
1:30-1:34 warning `guys` may be insensitive, use `people`, `persons`, `folks` instead gals-man retext-equality
⚠ 2 warnings
<p><em>Emphasis</em> and <em>stress</em>, you guys!</p>
Transforming between ecosystems
Ecosystems can be combined in two modes.
Bridge mode transforms the tree from one format (origin) to another
(destination).
A different processor runs on the destination tree.
Afterwards, the original processor continues with the origin tree.
Mutate mode also transforms the syntax tree from one format to another.
But the original processor continues transforming the destination tree.
In the previous example (“Programming interface”), remark-retext is used in
bridge mode: the origin syntax tree is kept after retext is done; whereas
remark-rehype is used in mutate mode: it sets a new syntax tree and discards
the origin tree.
The following plugins lets you combine ecosystems:
API
This package exports the identifier unified (the root processor).
There is no default export.
processor()
Create a new processor.
Returns
New unfrozen processor (processor).
This processor is configured to work the same as its ancestor.
When the descendant processor is configured in the future it does not affect
the ancestral processor.
Example
This example shows how a new processor can be created (from remark) and linked
to stdin(4) and stdout(4).
import process from 'node:process'
import concatStream from 'concat-stream'
import {remark} from 'remark'
process.stdin.pipe(
concatStream(function (buf) {
process.stdout.write(String(remark().processSync(buf)))
})
)
processor.compiler
Compiler to use (Compiler, optional).
processor.data([key[, value]])
Configure the processor with info available to all plugins.
Information is stored in an object.
Typically, options can be given to a specific plugin, but sometimes it makes
sense to have information shared with several plugins.
For example, a list of HTML elements that are self-closing, which is needed
during all phases.
👉 Note: setting information cannot occur on frozen
processors.
Call the processor first to create a new unfrozen processor.
👉 Note: to register custom data in TypeScript, augment the
Data interface.
Signatures
processor = processor.data(key, value)processor = processor.data(dataset)value = processor.data(key)dataset = processor.data()
Parameters
Returns
The current processor when setting (processor), the value at
key when getting (Data[key]), or the entire dataset when
getting without key (Data).
Example
This example show how to get and set info:
import {unified} from 'unified'
const processor = unified().data('alpha', 'bravo')
processor.data('alpha') // => 'bravo'
processor.data() // => {alpha: 'bravo'}
processor.data({charlie: 'delta'})
processor.data() // => {charlie: 'delta'}
processor.freeze()
Freeze a processor.
Frozen processors are meant to be extended and not to be configured directly.
When a processor is frozen it cannot be unfrozen.
New processors working the same way can be created by calling the processor.
It’s possible to freeze processors explicitly by calling .freeze().
Processors freeze automatically when .parse(), .run(), .runSync(),
.stringify(), .process(), or .processSync() are called.
Returns
The current processor (processor).
Example
This example, index.js, shows how rehype prevents extensions to itself:
import rehypeParse from 'rehype-parse'
import rehypeStringify from 'rehype-stringify'
import {unified} from 'unified'
export const rehype = unified().use(rehypeParse).use(rehypeStringify).freeze()
That processor can be used and configured like so:
import {rehype} from 'rehype'
import rehypeFormat from 'rehype-format'
// …
rehype()
.use(rehypeFormat)
// …
A similar looking example is broken as operates on the frozen interface.
If this behavior was allowed it would result in unexpected behavior so an error
is thrown.
This is not valid:
import {rehype} from 'rehype'
import rehypeFormat from 'rehype-format'
// …
rehype
.use(rehypeFormat)
// …
Yields:
~/node_modules/unified/index.js:426
throw new Error(
^
Error: Cannot call `use` on a frozen processor.
Create a new processor first, by calling it: use `processor()` instead of `processor`.
at assertUnfrozen (~/node_modules/unified/index.js:426:11)
at Function.use (~/node_modules/unified/index.js:165:5)
…
processor.parse(file)
Parse text to a syntax tree.
👉 Note: parse freezes the processor if not already
frozen.
👉 Note: parse performs the parse phase, not the run phase
or other phases.
Parameters
file (Compatible) — file to parse; typically
string or VFile; any value accepted as x in new VFile(x)
Returns
Syntax tree representing file (Node).
Example
This example shows how parse can be used to create a tree from a file.
import remarkParse from 'remark-parse'
import {unified} from 'unified'
const tree = unified().use(remarkParse).parse('# Hello world!')
console.log(tree)
Yields:
{
type: 'root',
children: [
{type: 'heading', depth: 1, children: [Array], position: [Object]}
],
position: {
start: {line: 1, column: 1, offset: 0},
end: {line: 1, column: 15, offset: 14}
}
}
processor.parser
Parser to use (Parser, optional).
processor.process(file[, done])
Process the given file as configured on the processor.
👉 Note: process freezes the processor if not already
frozen.
👉 Note: process performs the parse, run, and stringify
phases.
Signatures
processor.process(file, done)Promise<VFile> = processor.process(file?)
Parameters
Returns
Nothing if done is given (undefined).
Otherwise a promise, rejected with a fatal error or resolved with the
processed file (Promise<VFile>).
The parsed, transformed, and compiled value is available at file.value (see
note).
👉 Note: unified typically compiles by serializing: most
compilers return string (or Uint8Array).
Some compilers, such as the one configured with
rehype-react, return other values (in this case, a React
tree).
If you’re using a compiler that doesn’t serialize, expect different result
values.
To register custom results in TypeScript, add them to
CompileResultMap.
Example
This example shows how process can be used to process a file:
import rehypeDocument from 'rehype-document'
import rehypeFormat from 'rehype-format'
import rehypeStringify from 'rehype-stringify'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import {unified} from 'unified'
const file = await unified()
.use(remarkParse)
.use(remarkRehype)
.use(rehypeDocument, {title: '👋🌍'})
.use(rehypeFormat)
.use(rehypeStringify)
.process('# Hello world!')
console.log(String(file))
Yields:
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>👋🌍</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Hello world!</h1>
</body>
</html>
processor.processSync(file)
Process the given file as configured on the processor.
An error is thrown if asynchronous transforms are configured.
👉 Note: processSync freezes the processor if not already
frozen.
👉 Note: processSync performs the parse, run, and stringify
phases.
Parameters
file (Compatible, optional) — file; typically
string or VFile; any value accepted as x in new VFile(x)
Returns
The processed file (VFile).
The parsed, transformed, and compiled value is available at file.value (see
note).
👉 Note: unified typically compiles by serializing: most
compilers return string (or Uint8Array).
Some compilers, such as the one configured with
rehype-react, return other values (in this case, a React
tree).
If you’re using a compiler that doesn’t serialize, expect different result
values.
To register custom results in TypeScript, add them to
CompileResultMap.
Example
This example shows how processSync can be used to process a file, if all
transformers are synchronous.
import rehypeDocument from 'rehype-document'
import rehypeFormat from 'rehype-format'
import rehypeStringify from 'rehype-stringify'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import {unified} from 'unified'
const processor = unified()
.use(remarkParse)
.use(remarkRehype)
.use(rehypeDocument, {title: '👋🌍'})
.use(rehypeFormat)
.use(rehypeStringify)
console.log(String(processor.processSync('# Hello world!')))
Yields:
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>👋🌍</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Hello world!</h1>
</body>
</html>
processor.run(tree[, file][, done])
Run transformers on a syntax tree.
👉 Note: run freezes the processor if not already
frozen.
👉 Note: run performs the run phase, not other phases.
Signatures
processor.run(tree, done)processor.run(tree, file, done)Promise<Node> = processor.run(tree, file?)
Parameters
tree (Node) — tree to transform and inspectfile (Compatible, optional) — file associated
with node; any value accepted as x in new VFile(x)done (RunCallback, optional) — callback
Returns
Nothing if done is given (undefined).
Otherwise, a promise rejected with a fatal error or resolved with the
transformed tree (Promise<Node>).
Example
This example shows how run can be used to transform a tree:
import remarkReferenceLinks from 'remark-reference-links'
import {unified} from 'unified'
import {u} from 'unist-builder'
const tree = u('root', [
u('paragraph', [
u('link', {href: 'https://example.com'}, [u('text', 'Example Domain')])
])
])
const changedTree = await unified().use(remarkReferenceLinks).run(tree)
console.log(changedTree)
Yields:
{
type: 'root',
children: [
{type: 'paragraph', children: [Array]},
{type: 'definition', identifier: '1', title: '', url: undefined}
]
}
processor.runSync(tree[, file])
Run transformers on a syntax tree.
An error is thrown if asynchronous transforms are configured.
👉 Note: runSync freezes the processor if not already
frozen.
👉 Note: runSync performs the run phase, not other phases.
Parameters
tree (Node) — tree to transform and inspectfile (Compatible, optional) — file associated
with node; any value accepted as x in new VFile(x)
Returns
Transformed tree (Node).
processor.stringify(tree[, file])
Compile a syntax tree.
👉 Note: stringify freezes the processor if not already
frozen.
👉 Note: stringify performs the stringify phase, not the run
phase or other phases.
Parameters
tree (Node) — tree to compilefile (Compatible, optional) — file associated
with node; any value accepted as x in new VFile(x)
Returns
Textual representation of the tree (Uint8Array or string, see note).
👉 Note: unified typically compiles by serializing: most compilers
return string (or Uint8Array).
Some compilers, such as the one configured with
rehype-react, return other values (in this case, a
React tree).
If you’re using a compiler that doesn’t serialize, expect different
result values.
To register custom results in TypeScript, add them to
CompileResultMap.
Example
This example shows how stringify can be used to serialize a syntax tree:
import {h} from 'hastscript'
import rehypeStringify from 'rehype-stringify'
import {unified} from 'unified'
const tree = h('h1', 'Hello world!')
const document = unified().use(rehypeStringify).stringify(tree)
console.log(document)
Yields:
<h1>Hello world!</h1>
processor.use(plugin[, options])
Configure the processor to use a plugin, a list of usable values, or a preset.
If the processor is already using a plugin, the previous plugin configuration
is changed based on the options that are passed in.
In other words, the plugin is not added a second time.
👉 Note: use cannot be called on frozen processors.
Call the processor first to create a new unfrozen processor.
Signatures
processor.use(preset?)processor.use(list)processor.use(plugin[, ...parameters])
Parameters
preset (Preset) — plugins and settingslist (PluggableList) — list of usable thingsplugin (Plugin) — pluginparameters (Array<unknown>) — configuration for plugin, typically a
single options object
Returns
Current processor (processor).
Example
There are many ways to pass plugins to .use().
This example gives an overview:
import {unified} from 'unified'
unified()
// Plugin with options:
.use(pluginA, {x: true, y: true})
// Passing the same plugin again merges configuration (to `{x: true, y: false, z: true}`):
.use(pluginA, {y: false, z: true})
// Plugins:
.use([pluginB, pluginC])
// Two plugins, the second with options:
.use([pluginD, [pluginE, {}]])
// Preset with plugins and settings:
.use({plugins: [pluginF, [pluginG, {}]], settings: {position: false}})
// Settings only:
.use({settings: {position: false}})
CompileResultMap
Interface of known results from compilers (TypeScript type).
Normally, compilers result in text (Value of vfile).
When you compile to something else, such as a React node (as in,
rehype-react), you can augment this interface to include that type.
import type {ReactNode} from 'somewhere'
declare module 'unified' {
interface CompileResultMap {
// Register a new result (value is used, key should match it).
ReactNode: ReactNode
}
}
export {} // You may not need this, but it makes sure the file is a module.
Use CompileResults to access the values.
Type
interface CompileResultMap {
// Note: if `Value` from `VFile` is changed, this should too.
Uint8Array: Uint8Array
string: string
}
CompileResults
Acceptable results from compilers (TypeScript type).
To register custom results, add them to
CompileResultMap.
Type
type CompileResults = CompileResultMap[keyof CompileResultMap]
Compiler
A compiler handles the compiling of a syntax tree to something else
(in most cases, text) (TypeScript type).
It is used in the stringify phase and called with a Node
and VFile representation of the document to compile.
It should return the textual representation of the given tree (typically
string).
👉 Note: unified typically compiles by serializing: most compilers
return string (or Uint8Array).
Some compilers, such as the one configured with
rehype-react, return other values (in this case, a
React tree).
If you’re using a compiler that doesn’t serialize, expect different
result values.
To register custom results in TypeScript, add them to
CompileResultMap.
Type
type Compiler<
Tree extends Node = Node,
Result extends CompileResults = CompileResults
> = (tree: Tree, file: VFile) => Result
Data
Interface of known data that can be supported by all plugins (TypeScript type).
Typically, options can be given to a specific plugin, but sometimes it makes
sense to have information shared with several plugins.
For example, a list of HTML elements that are self-closing, which is needed
during all phases.
To type this, do something like:
declare module 'unified' {
interface Data {
htmlVoidElements?: Array<string> | undefined
}
}
export {} // You may not need this, but it makes sure the file is a module.
Type
interface Data {
settings?: Settings | undefined
}
See Settings for more info.
Parser
A parser handles the parsing of text to a syntax tree (TypeScript type).
It is used in the parse phase and is called with a string and
VFile of the document to parse.
It must return the syntax tree representation of the given file
(Node).
Type
type Parser<Tree extends Node = Node> = (document: string, file: VFile) => Tree
Pluggable
Union of the different ways to add plugins and settings (TypeScript type).
Type
type Pluggable =
| Plugin<Array<any>, any, any>
| PluginTuple<Array<any>, any, any>
| Preset
See Plugin, PluginTuple,
and Preset for more info.
PluggableList
List of plugins and presets (TypeScript type).
Type
type PluggableList = Array<Pluggable>
See Pluggable for more info.
Plugin
Single plugin (TypeScript type).
Plugins configure the processors they are applied on in the following ways:
- they change the processor, such as the parser, the compiler, or by
configuring data
- they specify how to handle trees and files
In practice, they are functions that can receive options and configure the
processor (this).
👉 Note: plugins are called when the processor is frozen, not when they
are applied.
Type
type Plugin<
PluginParameters extends unknown[] = [],
Input extends Node | string | undefined = Node,
Output = Input
> = (
this: Processor,
...parameters: PluginParameters
) => Input extends string // Parser.
? Output extends Node | undefined
? undefined | void
: never
: Output extends CompileResults // Compiler.
? Input extends Node | undefined
? undefined | void
: never
: // Inspect/transform.
| Transformer<
Input extends Node ? Input : Node,
Output extends Node ? Output : Node
>
| undefined
| void
See Transformer for more info.
Example
move.js:
/**
* @typedef Options
* Configuration (required).
* @property {string} extname
* File extension to use (must start with `.`).
*/
/** @type {import('unified').Plugin<[Options]>} */
export function move(options) {
if (!options || !options.extname) {
throw new Error('Missing `options.extname`')
}
return function (_, file) {
if (file.extname && file.extname !== options.extname) {
file.extname = options.extname
}
}
}
example.md:
# Hello, world!
example.js:
import rehypeStringify from 'rehype-stringify'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import {read, write} from 'to-vfile'
import {unified} from 'unified'
import {reporter} from 'vfile-reporter'
import {move} from './move.js'
const file = await unified()
.use(remarkParse)
.use(remarkRehype)
.use(move, {extname: '.html'})
.use(rehypeStringify)
.process(await read('example.md'))
console.error(reporter(file))
await write(file) // Written to `example.html`.
Yields:
example.md: no issues found
…and in example.html:
<h1>Hello, world!</h1>
PluginTuple
Tuple of a plugin and its configuration (TypeScript type).
The first item is a plugin, the rest are its parameters.
Type
type PluginTuple<
TupleParameters extends unknown[] = [],
Input extends Node | string | undefined = undefined,
Output = undefined
> = [
plugin: Plugin<TupleParameters, Input, Output>,
...parameters: TupleParameters
]
See Plugin for more info.
Preset
Sharable configuration (TypeScript type).
They can contain plugins and settings.
Fields
plugins (PluggableList, optional)
— list of plugins and presetssettings (Data, optional)
— shared settings for parsers and compilers
Example
preset.js:
import remarkCommentConfig from 'remark-comment-config'
import remarkLicense from 'remark-license'
import remarkPresetLintConsistent from 'remark-preset-lint-consistent'
import remarkPresetLintRecommended from 'remark-preset-lint-recommended'
import remarkToc from 'remark-toc'
/** @type {import('unified').Preset} */
const preset = {
plugins: [
remarkPresetLintRecommended,
remarkPresetLintConsistent,
remarkCommentConfig,
[remarkToc, {maxDepth: 3, tight: true}],
remarkLicense
]
settings: {bullet: '*', emphasis: '*', fences: true},
}
export default preset
example.md:
# Hello, world!
_Emphasis_ and **importance**.
## Table of contents
## API
## License
example.js:
import {remark} from 'remark'
import {read, write} from 'to-vfile'
import {reporter} from 'vfile-reporter'
import preset from './preset.js'
const file = await remark()
.use(preset)
.process(await read('example.md'))
console.error(reporter(file))
await write(file)
Yields:
example.md: no issues found
example.md now contains:
# Hello, world!
*Emphasis* and **importance**.
## Table of contents
* [API](https://www.npmjs.com/package/unified#api)
* [License](https://www.npmjs.com/package/unified#license)
## API
## License
[MIT](license) © [Titus Wormer](https://wooorm.com)
ProcessCallback
Callback called when the process is done (TypeScript type).
Called with either an error or a result.
Parameters
error (Error, optional)
— fatal errorfile (VFile, optional)
— processed file
Returns
Nothing (undefined).
Example
This example shows how process can be used to process a file with a callback.
import remarkGithub from 'remark-github'
import remarkParse from 'remark-parse'
import remarkStringify from 'remark-stringify'
import {unified} from 'unified'
import {reporter} from 'vfile-reporter'
unified()
.use(remarkParse)
.use(remarkGithub)
.use(remarkStringify)
.process('@unifiedjs', function (error, file) {
if (error) throw error
if (file) {
console.error(reporter(file))
console.log(String(file))
}
})
Yields:
no issues found
[**@unifiedjs**](https://github.com/unifiedjs)
Processor
Type of a processor (TypeScript type).
RunCallback
Callback called when transformers are done (TypeScript type).
Called with either an error or results.
Parameters
error (Error, optional)
— fatal errortree (Node, optional)
— transformed treefile (VFile, optional)
— file
Returns
Nothing (undefined).
Settings
Interface of known extra options, that can be supported by parser and
compilers.
This exists so that users can use packages such as remark, which configure
both parsers and compilers (in this case remark-parse and
remark-stringify), and still provide options for them.
When you make parsers or compilers, that could be packaged up together, you
should support this.data('settings') as input and merge it with explicitly
passed options.
Then, to type it, using remark-stringify as an example, do something like:
declare module 'unified' {
interface Settings {
bullet: '*' | '+' | '-'
// …
}
}
export {} // You may not need this, but it makes sure the file is a module.
Type
interface Settings {}
TransformCallback
Callback passed to transforms (TypeScript type).
If the signature of a transformer accepts a third argument, the transformer
may perform asynchronous operations, and must call it.
Parameters
error (Error, optional)
— fatal error to stop the processtree (Node, optional)
— new, changed, treefile (VFile, optional)
— new, changed, file
Returns
Nothing (undefined).
Transformer
Transformers handle syntax trees and files (TypeScript type).
They are functions that are called each time a syntax tree and file are
passed through the run phase.
When an error occurs in them (either because it’s thrown, returned,
rejected, or passed to next), the process stops.
The run phase is handled by trough, see its documentation for
the exact semantics of these functions.
👉 Note: you should likely ignore next: don’t accept it.
it supports callback-style async work.
But promises are likely easier to reason about.
Type
type Transformer<
Input extends Node = Node,
Output extends Node = Input
> = (
tree: Input,
file: VFile,
next: TransformCallback<Output>
) =>
| Promise<Output | undefined>
| Output
| Error
| undefined
Types
This package is fully typed with TypeScript.
It exports the additional types
CompileResultMap,
CompileResults,
Compiler,
Data,
Parser,
Pluggable,
PluggableList,
Plugin,
PluginTuple,
Preset,
ProcessCallback,
Processor,
RunCallback,
Settings,
TransformCallback,
and Transformer
For TypeScript to work, it is particularly important to type your plugins
correctly.
We strongly recommend using the Plugin type with its generics and to use the
node types for the syntax trees provided by our packages (as in,
@types/hast, @types/mdast,
@types/nlcst).
/**
* @typedef {import('hast').Root} HastRoot
* @typedef {import('mdast').Root} MdastRoot
*/
/**
* @typedef Options
* Configuration (optional).
* @property {boolean | null | undefined} [someField]
* Some option (optional).
*/
// To type options:
/** @type {import('unified').Plugin<[(Options | null | undefined)?]>} */
export function myPluginAcceptingOptions(options) {
const settings = options || {}
// `settings` is now `Options`.
}
// To type a plugin that works on a certain tree, without options:
/** @type {import('unified').Plugin<[], MdastRoot>} */
export function myRemarkPlugin() {
return function (tree, file) {
// `tree` is `MdastRoot`.
}
}
// To type a plugin that transforms one tree into another:
/** @type {import('unified').Plugin<[], MdastRoot, HastRoot>} */
export function remarkRehype() {
return function (tree) {
// `tree` is `MdastRoot`.
// Result must be `HastRoot`.
}
}
// To type a plugin that defines a parser:
/** @type {import('unified').Plugin<[], string, MdastRoot>} */
export function remarkParse(options) {}
// To type a plugin that defines a compiler:
/** @type {import('unified').Plugin<[], HastRoot, string>} */
export function rehypeStringify(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, unified@^11, compatible
with Node.js 16.
Contribute
See contributing.md in unifiedjs/.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.
For info on how to submit a security report, see our
security policy.
Sponsor
Support this effort and give back by sponsoring on OpenCollective!
Acknowledgments
Preliminary work for unified was done in 2014 for
retext and inspired by ware.
Further incubation happened in remark.
The project was finally externalised in 2015 and published as unified.
The project was authored by @wooorm.
Although unified since moved its plugin architecture to trough,
thanks to @calvinfo,
@ianstormtaylor, and others for their
work on ware, as it was a huge initial inspiration.
License
MIT © Titus Wormer
