unified is an interface for processing text using syntax trees. It’s what powers remark (Markdown), retext (natural language), and rehype (HTML), and allows for processing between formats.
unified enables new exciting projects like Gatsby to pull in Markdown, MDX to embed JSX, and Prettier to format it. It’s used in about 500k projects on GitHub and has about 25m downloads each month on npm: you’re probably using it. Some notable users are Node.js, Vercel, Netlify, GitHub, Mozilla, WordPress, Adobe, Facebook, Google, and many more.
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npm:
npm install unifiedThis package comes with types.
If you’re using TypeScript, make sure to also install
@types/unist.
var unified = require('unified')
var markdown = require('remark-parse')
var remark2rehype = require('remark-rehype')
var doc = require('rehype-document')
var format = require('rehype-format')
var html = require('rehype-stringify')
var report = require('vfile-reporter')
unified()
.use(markdown)
.use(remark2rehype)
.use(doc, {title: '👋🌍'})
.use(format)
.use(html)
.process('# Hello world!', function (err, file) {
console.error(report(err || 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>unified is an interface for processing text using syntax trees. Syntax trees are a representation of text 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 |
+--------------+
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.
The syntax trees used in unified are unist nodes.
A node is a plain JavaScript objects with a type field.
The semantics of nodes and format of syntax trees is defined by other projects.
There are several utilities for working with nodes.
The following projects process different syntax tree formats. They parse text to a syntax tree and compile that back to text. These processors can be used as is, or their parser and compiler can be mixed and matched with unified and plugins to process between different syntaxes.
The below plugins work with unified, on all syntax tree formats:
unified-diff— Ignore messages for unchanged lines in Travisunified-message-control— Enable, disable, and ignore messages
See remark, rehype, and retext for their lists of plugins.
When processing a document, metadata is often gathered about that document. vfile is a virtual file format that stores data, metadata, and messages about files for unified and its plugins.
There are several utilities for working with these files.
Processors are configured with plugins or
with the data method.
unified can integrate with the file system with unified-engine.
CLI apps can be created with unified-args, Gulp plugins with
unified-engine-gulp, and Atom Linters with
unified-engine-atom.
unified-stream provides a streaming interface.
The API provided by unified allows multiple files to be processed and gives access to metadata (such as lint messages):
var unified = require('unified')
var markdown = require('remark-parse')
var styleGuide = require('remark-preset-lint-markdown-style-guide')
var remark2retext = require('remark-retext')
var english = require('retext-english')
var equality = require('retext-equality')
var remark2rehype = require('remark-rehype')
var html = require('rehype-stringify')
var report = require('vfile-reporter')
unified()
.use(markdown)
.use(styleGuide)
.use(remark2retext, unified().use(english).use(equality))
.use(remark2rehype)
.use(html)
.process('*Emphasis* and _stress_, you guys!', function (err, file) {
console.error(report(err || 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-men retext-equality
⚠ 2 warnings<p><em>Emphasis</em> and <em>stress</em>, you guys!</p>Processors can be combined in two modes.
Bridge mode transforms the syntax tree from one format (origin) to another (destination). Another processor runs on the destination tree. Finally, the original processor continues transforming 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.
Processor describing how to process text.
Function — New unfrozen processor that 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.
The following example shows how a new processor can be created (from the remark processor) and linked to stdin(4) and stdout(4).
var remark = require('remark')
var concat = require('concat-stream')
process.stdin.pipe(concat(onconcat))
function onconcat(buf) {
var doc = remark().processSync(buf).toString()
process.stdout.write(doc)
}Configure the processor to use a plugin and optionally configure that plugin with options.
If the processor is already using this plugin, the previous plugin configuration is changed based on the options that are passed in. The plugin is not added a second time.
processor.use(plugin[, options])processor.use(preset)processor.use(list)
plugin(Attacher)options(*, optional) — Configuration forpluginpreset(Object) — Object with an optionalplugins(set tolist), and/or an optionalsettingsobjectlist(Array) — List of plugins, presets, and pairs (pluginandoptionsin an array)
processor — The processor that use was called on.
use cannot be called on frozen processors.
Call the processor first to create a new unfrozen processor.
There are many ways to pass plugins to .use().
The below example gives an overview.
var unified = require('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}})Parse text to a syntax tree.
Node — Parsed syntax tree representing file.
parse freezes the processor if not already frozen.
parse performs the parse phase, not the run phase or other
phases.
The below example shows how parse can be used to create a syntax tree from a
file.
var unified = require('unified')
var markdown = require('remark-parse')
var tree = unified().use(markdown).parse('# Hello world!')
console.log(tree)Yields:
{
type: 'root',
children: [
{type: 'heading', depth: 1, children: [Array], position: [Position]}
],
position: {
start: {line: 1, column: 1, offset: 0},
end: {line: 1, column: 15, offset: 14}
}
}A parser handles the parsing of text to a syntax tree.
Used in the parse phase and called with a string and
VFile representation of the text to parse.
Parser can be a function, in which case it must return a Node: the
syntax tree representation of the given file.
Parser can also be a constructor function (a function with a parse field, or
other fields, in its prototype), in which case it’s constructed with new.
Instances must have a parse method that is called without arguments and must
return a Node.
Compile a syntax tree.
node(Node) — Syntax tree to compilefile(VFile, optional) — File, any value accepted byvfile()
string or Buffer (see notes) — Textual representation of the syntax
tree
stringify freezes the processor if not already frozen.
stringify performs the stringify phase, not the run phase
or other phases.
unified typically compiles by serializing: most compilers return
string (or Buffer).
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 doesn’t serialize, expect different result values.
When using TypeScript, cast the type on your side.
The below example shows how stringify can be used to serialize a syntax tree.
var unified = require('unified')
var html = require('rehype-stringify')
var h = require('hastscript')
var tree = h('h1', 'Hello world!')
var doc = unified().use(html).stringify(tree)
console.log(doc)Yields:
<h1>Hello world!</h1>A compiler handles the compiling of a syntax tree to text.
Used in the stringify phase and called with a Node
and VFile representation of syntax tree to compile.
Compiler can be a function, in which case it should return a string: the
textual representation of the syntax tree.
Compiler can also be a constructor function (a function with a compile
field, or other fields, in its prototype), in which case it’s constructed with
new.
Instances must have a compile method that is called without arguments and
should return a string.
Run transformers on a syntax tree.
node(Node) — Syntax tree to run onfile(VFile, optional) — File, any value accepted byvfile()done(Function, optional) — Callback
Promise if done is not given.
The returned promise is rejected with a fatal error, or resolved with the
transformed syntax tree.
run freezes the processor if not already frozen.
run performs the run phase, not other phases.
Callback called when transformers are done. Called with either an error or results.
err(Error, optional) — Fatal errornode(Node, optional) — Transformed syntax treefile(VFile, optional) — File
The below example shows how run can be used to transform a syntax tree.
var unified = require('unified')
var references = require('remark-reference-links')
var u = require('unist-builder')
var tree = u('root', [
u('paragraph', [
u('link', {href: 'https://example.com'}, [u('text', 'Example Domain')])
])
])
unified()
.use(references)
.run(tree, function (err, tree) {
if (err) throw err
console.log(tree)
})Yields:
{
type: 'root',
children: [
{type: 'paragraph', children: [Array]},
{type: 'definition', identifier: '1', title: undefined, url: undefined}
]
}Run transformers on a syntax tree.
An error is thrown if asynchronous plugins are configured.
node(Node) — Syntax tree to run onfile(VFile, optional) — File, any value accepted byvfile()
Node — Transformed syntax tree.
runSync freezes the processor if not already frozen.
runSync performs the run phase, not other phases.
Process the given file as configured on the processor.
Promise if done is not given.
The returned promise is rejected with a fatal error, or resolved with the
processed file.
The parsed, transformed, and compiled value is exposed on
file.contents or file.result (see notes).
process freezes the processor if not already frozen.
process performs the parse, run, and stringify phases.
unified typically compiles by serializing: most compilers return
string (or Buffer).
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 serializes, the result is available at
file.contents.
Otherwise, the result is available at file.result.
The below example shows how process can be used to process a file, whether
transformers are asynchronous or not, with promises.
var unified = require('unified')
var markdown = require('remark-parse')
var remark2rehype = require('remark-rehype')
var doc = require('rehype-document')
var format = require('rehype-format')
var html = require('rehype-stringify')
unified()
.use(markdown)
.use(remark2rehype)
.use(doc, {title: '👋🌍'})
.use(format)
.use(html)
.process('# Hello world!')
.then(
function (file) {
console.log(String(file))
},
function (err) {
console.error(String(err))
}
)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>Callback called when the process is done. Called with a fatal error, if any, and a file.
The below example shows how process can be used to process a file, whether
transformers are asynchronous or not, with a callback.
var unified = require('unified')
var parse = require('remark-parse')
var stringify = require('remark-stringify')
var github = require('remark-github')
var report = require('vfile-reporter')
unified()
.use(parse)
.use(github)
.use(stringify)
.process('@wooorm', function (err, file) {
console.error(report(err || file))
console.log(String(file))
})Yields:
no issues found[**@wooorm**](https://github.com/wooorm)Process the given file as configured on the processor.
An error is thrown if asynchronous plugins are configured.
The parsed, transformed, and compiled value is exposed on
file.contents or file.result (see notes).
processSync freezes the processor if not already frozen.
processSync performs the parse, run, and stringify
phases.
unified typically compiles by serializing: most compilers return
string (or Buffer).
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 serializes, the result is available at
file.contents.
Otherwise, the result is available at file.result.
The below example shows how processSync can be used to process a file, if all
transformers are synchronous.
var unified = require('unified')
var markdown = require('remark-parse')
var remark2rehype = require('remark-rehype')
var doc = require('rehype-document')
var format = require('rehype-format')
var html = require('rehype-stringify')
var processor = unified()
.use(markdown)
.use(remark2rehype)
.use(doc, {title: '👋🌍'})
.use(format)
.use(html)
console.log(processor.processSync('# Hello world!').toString())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>Configure the processor with information available to all plugins. Information is stored in an in-memory key-value store.
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 of the process.
processor = processor.data(key, value)processor = processor.data(values)value = processor.data(key)info = processor.data()
key(string, optional) — Identifiervalue(*, optional) — Value to setvalues(Object, optional) — Values to set
processor— If setting, the processor thatdatais called onvalue(*) — If getting, the value atkeyinfo(Object) — Without arguments, the key-value store
Setting information cannot occur on frozen processors. Call the processor first to create a new unfrozen processor.
The following example show how to get and set information:
var unified = require('unified')
var processor = unified().data('alpha', 'bravo')
processor.data('alpha') // => 'bravo'
processor.data() // {alpha: 'bravo'}
processor.data({charlie: 'delta'})
processor.data() // {charlie: 'delta'}Freeze a processor. Frozen processors are meant to be extended and not to be configured directly.
Once 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 implicitly when .parse(), .run(),
.runSync(), .stringify(), .process(),
or .processSync() are called.
processor — The processor that freeze was called on.
The following example, index.js, shows how rehype prevents extensions to
itself:
var unified = require('unified')
var parse = require('rehype-parse')
var stringify = require('rehype-stringify')
module.exports = unified().use(parse).use(stringify).freeze()The below example, a.js, shows how that processor can be used and configured.
var rehype = require('rehype')
var format = require('rehype-format')
// …
rehype()
.use(format)
// …The below example, b.js, shows a similar looking example that operates on the
frozen rehype interface because it does not call rehype.
If this behavior was allowed it would result in unexpected behavior so an
error is thrown.
This is invalid:
var rehype = require('rehype')
var format = require('rehype-format')
// …
rehype
.use(format)
// …Yields:
~/node_modules/unified/index.js:440
throw new Error(
^
Error: Cannot invoke `use` on a frozen processor.
Create a new processor first, by invoking it: use `processor()` instead of `processor`.
at assertUnfrozen (~/node_modules/unified/index.js:440:11)
at Function.use (~/node_modules/unified/index.js:172:5)
at Object.<anonymous> (~/b.js:6:4)Plugins configure the processors they are applied on in the following ways:
- They change the processor: such as the parser, the compiler, or configuring data
- They specify how to handle syntax trees and files
Plugins are a concept.
They materialize as attachers.
move.js:
module.exports = move
function move(options) {
var expected = (options || {}).extname
if (!expected) {
throw new Error('Missing `extname` in options')
}
return transformer
function transformer(tree, file) {
if (file.extname && file.extname !== expected) {
file.extname = expected
}
}
}index.md:
# Hello, world!index.js:
var unified = require('unified')
var parse = require('remark-parse')
var remark2rehype = require('remark-rehype')
var stringify = require('rehype-stringify')
var vfile = require('to-vfile')
var report = require('vfile-reporter')
var move = require('./move')
unified()
.use(parse)
.use(remark2rehype)
.use(move, {extname: '.html'})
.use(stringify)
.process(vfile.readSync('index.md'), function (err, file) {
console.error(report(err || file))
if (file) {
vfile.writeSync(file) // Written to `index.html`.
}
})Yields:
index.md: no issues foundindex.html:
<h1>Hello, world!</h1>Attachers are materialized plugins. An attacher is a function that can receive options and configures the processor.
Attachers change the processor, such as the parser, the compiler, configuring data, or by specifying how the syntax tree or file are handled.
The context object (this) is set to the processor the attacher is applied on.
options(*, optional) — Configuration
transformer — Optional.
Attachers are called when the processor is frozen, not when they are applied.
Transformers handle syntax trees and files.
A transformer is a function that is called each time a syntax tree and file are
passed through the run phase.
If an error occurs (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.
node(Node) — Syntax tree to handlefile(VFile) — File to handlenext(Function, optional)
void— If nothing is returned, the next transformer keeps using same tree.Error— Fatal error to stop the processnode(Node) — New syntax tree. If returned, the next transformer is given this new treePromise— Returned to perform an asynchronous operation. The promise must be resolved (optionally with aNode) or rejected (optionally with anError)
If the signature of a transformer includes next (the third
argument), the transformer may perform asynchronous operations, and must
call next().
err(Error, optional) — Fatal error to stop the processnode(Node, optional) — New syntax tree. If given, the next transformer is given this new treefile(VFile, optional) — New file. If given, the next transformer is given this new file
Presets are sharable configuration. They can contain plugins and settings.
preset.js:
exports.settings = {bullet: '*', emphasis: '*', fences: true}
exports.plugins = [
require('remark-preset-lint-recommended'),
require('remark-preset-lint-consistent'),
require('remark-comment-config'),
[require('remark-toc'), {maxDepth: 3, tight: true}],
require('remark-license')
]readme.md:
# Hello, world!
_Emphasis_ and **importance**.
## Table of contents
## API
## Licenseindex.js:
var remark = require('remark')
var vfile = require('to-vfile')
var report = require('vfile-reporter')
var preset = require('./preset')
remark()
.use(preset)
.process(vfile.readSync('readme.md'), function (err, file) {
console.error(report(err || file))
if (file) {
vfile.writeSync(file)
}
})Yields:
readme.md: no issues foundreadme.md now contains:
# Hello, world!
*Emphasis* and **importance**.
## Table of contents
* [API](#api)
* [License](#license)
## API
## License
[MIT](license) © [Titus Wormer](https://wooorm.com)See contributing.md in unifiedjs/.github for ways
to get started.
See support.md for ways to get help.
Ideas for new plugins and tools can be posted in unifiedjs/ideas.
A curated list of awesome unified resources can be found in awesome unified.
This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.
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.