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unified

index.js
license
package.json
readme.md
types/

readme.md

[![unified][logo]][site]

[![Build][build-badge]][build] [![Coverage][coverage-badge]][coverage] [![Downloads][downloads-badge]][downloads] [![Size][size-badge]][size] [![Sponsors][sponsors-badge]][collective] [![Backers][backers-badge]][collective] [![Chat][chat-badge]][chat]

unified is an interface for processing text using syntax trees. It’s what powers [remark][remark] (Markdown), [retext][retext] (natural language), and [rehype][rehype] (HTML), and allows for processing between formats.

Intro

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.

To read about what we are up to, follow us [Twitter][]
For a less technical and more practical introduction to unified, visit [unifiedjs.com][site] and peruse its [Learn][] section
Browse [awesome unified][awesome] to find out more about the ecosystem
Questions? Get help on [Discussions][chat]!
Check out [Contribute][] below to find out how to help out, or become a backer or sponsor on [OpenCollective][collective]

Install

[npm][]:

sh
npm install unified

This package comes with types. If you’re using TypeScript, make sure to also install [@types/unist][ts-unist].

Use

js
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:

txt
no issues found

html
<!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>

[Description](#description)
[API](#api)
- [processor()](#processor)
- [processor.use(plugin[, options])](#processoruseplugin-options)
- [processor.parse(file)](#processorparsefile)
- [processor.stringify(node[, file])](#processorstringifynode-file)
- [processor.run(node[, file][, done])](#processorrunnode-file-done)
- [processor.runSync(node[, file])](#processorrunsyncnode-file)
- [processor.process(file[, done])](#processorprocessfile-done)
- [processor.processSync(file|value)](#processorprocesssyncfilevalue)
- [processor.data([key[, value]])](#processordatakey-value)
- [processor.freeze()](#processorfreeze)
[Plugin](#plugin)
- [function attacher([options])](#function-attacheroptions)
- [function transformer(node, file[, next])](#function-transformernode-file-next)
[Preset](#preset)
[Contribute](#contribute)
[Acknowledgments](#acknowledgments)
[License](#license)

Description

unified is an interface for processing text using syntax trees. Syntax trees are a representation of text understandable to programs. Those programs, called [*plugin*][plugin]s, take these trees and inspect and modify them. To get to the syntax tree from text, there is a [*parser*][parser]. To get from that back to text, there is a [*compiler*][compiler]. This is the [*process*][process] of a *processor*.

ascii
| ........................ process ........................... |
| .......... parse ... | ... run ... | ... stringify ..........|

          +--------+                     +----------+
Input ->- | Parser | ->- Syntax Tree ->- | Compiler | ->- Output
          +--------+          |          +----------+
                              X
                              |
                       +--------------+
                       | Transformers |
                       +--------------+

Processors

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*][freeze] and they should be called to create a new processor before they are used.

Syntax trees

The syntax trees used in unified are [unist][unist] nodes. A [node][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*][unist-utilities] for working with nodes.

[hast][hast] — HTML
[mdast][mdast] — Markdown
[nlcst][nlcst] — Natural language
[xast][xast] — XML

List of processors

The following projects process different [*syntax tree*][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.

[rehype][rehype] ([*hast*][hast]) — HTML
[remark][remark] ([*mdast*][mdast]) — Markdown
[retext][retext] ([*nlcst*][nlcst]) — Natural language

List of plugins

The below [plugins][plugin] work with unified, on all [*syntax tree*][syntax-tree] formats:

[unified-diff](https://github.com/unifiedjs/unified-diff) — Ignore messages for unchanged lines in Travis
[unified-message-control](https://github.com/unifiedjs/unified-message-control) — Enable, disable, and ignore messages

See [remark][remark-plugins], [rehype][rehype-plugins], and [retext][retext-plugins] for their lists of plugins.

File

When processing a document, metadata is often gathered about that document. [vfile][vfile] is a virtual file format that stores data, metadata, and messages about files for unified and its plugins.

There are several [*utilities*][vfile-utilities] for working with these files.

Configuration

[*Processors*][processors] are configured with [*plugin*][plugin]s or with the [data][data] method.

Integrations

unified can integrate with the file system with [unified-engine][engine]. CLI apps can be created with [unified-args][args], Gulp plugins with [unified-engine-gulp][gulp], and Atom Linters with [unified-engine-atom][atom].

[unified-stream][stream] provides a streaming interface.

Programming interface

The API provided by unified allows multiple files to be processed and gives access to *metadata* (such as lint messages):

js
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:

txt
  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

html
<p><em>Emphasis</em> and <em>stress</em>, you guys!</p>

Processing between syntaxes

[*Processors*][processors] can be combined in two modes.

Bridge mode transforms the [*syntax tree*][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][retext] is done; whereas remark-rehype is used in *mutate* mode: it sets a new syntax tree and discards the origin tree.

[remark-retext][remark-retext]
[remark-rehype][remark-rehype]
[rehype-retext][rehype-retext]
[rehype-remark][rehype-remark]

API

`processor()`

[*Processor*][processors] describing how to *process* text.

Returns

Function — New [*unfrozen*][freeze] 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.

Example

The following example shows how a new processor can be created (from the remark processor) and linked to stdin(4) and stdout(4).

js
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)
}

`processor.use(plugin[, options])`

[*Configure*][configuration] the processor to use a [*plugin*][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.

Signatures

processor.use(plugin[, options])
processor.use(preset)
processor.use(list)

Parameters

plugin ([Attacher][plugin])
options (*, optional) — Configuration for plugin
preset (Object) — Object with an optional plugins (set to list), and/or an optional settings object
list (Array) — List of plugins, presets, and pairs (plugin and options in an array)

Returns

processor — The processor that use was called on.

Note

use cannot be called on [*frozen*][freeze] processors. Call the processor first to create a new unfrozen processor.

Example

There are many ways to pass plugins to .use(). The below example gives an overview.

js
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}})

`processor.parse(file)`

Parse text to a [*syntax tree*][syntax-tree].

Parameters

file ([VFile][vfile]) — [*File*][file], any value accepted by vfile()

Returns

[Node][node] — Parsed [*syntax tree*][syntax-tree] representing file.

Note

parse freezes the processor if not already [*frozen*][freeze].

parse performs the [*parse phase*][description], not the *run phase* or other phases.

Example

The below example shows how parse can be used to create a syntax tree from a file.

js
var unified = require('unified')
var markdown = require('remark-parse')

var tree = unified().use(markdown).parse('# Hello world!')

console.log(tree)

Yields:

js
{
  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}
  }
}

`processor.Parser`

A parser handles the parsing of text to a [*syntax tree*][syntax-tree]. Used in the [*parse phase*][description] and called with a string and [VFile][vfile] representation of the text to parse.

Parser can be a function, in which case it must return a [Node][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][node].

`processor.stringify(node[, file])`

Compile a [*syntax tree*][syntax-tree].

Parameters

node ([Node][node]) — [*Syntax tree*][syntax-tree] to compile
file ([VFile][vfile], optional) — [*File*][file], any value accepted by vfile()

Returns

string or Buffer (see notes) — Textual representation of the [*syntax tree*][syntax-tree]

Note

stringify freezes the processor if not already [*frozen*][freeze].

stringify performs the [*stringify phase*][description], not the *run phase* or other phases.

unified typically compiles by serializing: most [*compiler*][compiler]s return string (or Buffer). Some compilers, such as the one configured with [rehype-react][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.

Example

The below example shows how stringify can be used to serialize a syntax tree.

js
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:

html
<h1>Hello world!</h1>

`processor.Compiler`

A compiler handles the compiling of a [*syntax tree*][syntax-tree] to text. Used in the [*stringify phase*][description] and called with a [Node][node] and [VFile][file] 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.

`processor.run(node[, file][, done])`

Run [*transformers*][transformer] on a [*syntax tree*][syntax-tree].

Parameters

node ([Node][node]) — [*Syntax tree*][syntax-tree] to run on
file ([VFile][vfile], optional) — [*File*][file], any value accepted by vfile()
done ([Function][run-done], optional) — Callback

Returns

[Promise][promise] if done is not given. The returned promise is rejected with a fatal error, or resolved with the transformed [*syntax tree*][syntax-tree].

Note

run freezes the processor if not already [*frozen*][freeze].

run performs the [*run phase*][description], not other phases.

`function done(err[, node, file])`

Callback called when [*transformers*][transformer] are done. Called with either an error or results.

Parameters

err (Error, optional) — Fatal error
node ([Node][node], optional) — Transformed [*syntax tree*][syntax-tree]
file ([VFile][vfile], optional) — [*File*][file]

Example

The below example shows how run can be used to transform a syntax tree.

js
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:

js
{
  type: 'root',
  children: [
    {type: 'paragraph', children: [Array]},
    {type: 'definition', identifier: '1', title: undefined, url: undefined}
  ]
}

`processor.runSync(node[, file])`

Run [*transformers*][transformer] on a [*syntax tree*][syntax-tree].

An error is thrown if asynchronous [*plugin*][plugin]s are configured.

Parameters

node ([Node][node]) — [*Syntax tree*][syntax-tree] to run on
file ([VFile][vfile], optional) — [*File*][file], any value accepted by vfile()

Returns

[Node][node] — Transformed [*syntax tree*][syntax-tree].

Note

runSync freezes the processor if not already [*frozen*][freeze].

runSync performs the [*run phase*][description], not other phases.

`processor.process(file[, done])`

[*Process*][description] the given [*file*][file] as configured on the processor.

Parameters

file ([VFile][vfile]) — [*File*][file], any value accepted by vfile()
done ([Function][process-done], optional) — Callback

Returns

[Promise][promise] if done is not given. The returned promise is rejected with a fatal error, or resolved with the processed [*file*][file].

The parsed, transformed, and compiled value is exposed on [file.contents][vfile-contents] or file.result (see notes).

Note

process freezes the processor if not already [*frozen*][freeze].

process performs the [*parse*, *run*, and *stringify* phases][description].

unified typically compiles by serializing: most [*compiler*][compiler]s return string (or Buffer). Some compilers, such as the one configured with [rehype-react][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.

Example

The below example shows how process can be used to process a file, whether transformers are asynchronous or not, with promises.

js
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:

html
<!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>

`function done(err, file)`

Callback called when the [*process*][description] is done. Called with a fatal error, if any, and a [*file*][file].

Parameters

err (Error, optional) — Fatal error
file ([VFile][vfile]) — Processed [*file*][file]

Example

The below example shows how process can be used to process a file, whether transformers are asynchronous or not, with a callback.

js
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:

txt
no issues found

markdown
[**@wooorm**](https://github.com/wooorm)

`processor.processSync(file|value)`

[*Process*][description] the given [*file*][file] as configured on the processor.

An error is thrown if asynchronous [*plugin*][plugin]s are configured.

Parameters

file ([VFile][vfile]) — [*File*][file], any value accepted by vfile()

Returns

([VFile][vfile]) — Processed [*file*][file]

The parsed, transformed, and compiled value is exposed on [file.contents][vfile-contents] or file.result (see notes).

Note

processSync freezes the processor if not already [*frozen*][freeze].

processSync performs the [*parse*, *run*, and *stringify* phases][description].

unified typically compiles by serializing: most [*compiler*][compiler]s return string (or Buffer). Some compilers, such as the one configured with [rehype-react][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.

Example

The below example shows how processSync can be used to process a file, if all transformers are synchronous.

js
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:

html
<!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.data([key[, value]])`

[*Configure*][configuration] the processor with information available to all [*plugin*][plugin]s. 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*][description] of the *process*.

Signatures

processor = processor.data(key, value)
processor = processor.data(values)
value = processor.data(key)
info = processor.data()

Parameters

key (string, optional) — Identifier
value (*, optional) — Value to set
values (Object, optional) — Values to set

Returns

processor — If setting, the processor that data is called on
value (*) — If getting, the value at key
info (Object) — Without arguments, the key-value store

Note

Setting information cannot occur on [*frozen*][freeze] processors. Call the processor first to create a new unfrozen processor.

Example

The following example show how to get and set information:

js
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'}

`processor.freeze()`

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()][parse], [.run()][run], [.runSync()][run-sync], [.stringify()][stringify], [.process()][process], or [.processSync()][process-sync] are called.

Returns

processor — The processor that freeze was called on.

Example

The following example, index.js, shows how rehype prevents extensions to itself:

js
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.

js
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:

js
var rehype = require('rehype')
var format = require('rehype-format')
// …

rehype
  .use(format)
  // …

Yields:

txt
~/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)

`Plugin`

Plugins [*configure*][configuration] the processors they are applied on in the following ways:

They change the processor: such as the [*parser*][parser], the [*compiler*][compiler], or configuring [*data*][data]
They specify how to handle [*syntax trees*][syntax-tree] and [*files*][file]

Plugins are a concept. They materialize as [attacher][attacher]s.

Example

move.js:

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:

markdown
# Hello, world!

index.js:

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:

txt
index.md: no issues found

index.html:

html
<h1>Hello, world!</h1>

`function attacher([options])`

Attachers are materialized [*plugin*][plugin]s. An attacher is a function that can receive options and [*configures*][configuration] the processor.

Attachers change the processor, such as the [*parser*][parser], the [*compiler*][compiler], configuring [*data*][data], or by specifying how the [*syntax tree*][syntax-tree] or [*file*][file] are handled.

Context

The context object (this) is set to the processor the attacher is applied on.

Parameters

options (*, optional) — Configuration

Returns

[transformer][transformer] — Optional.

Note

Attachers are called when the processor is [*frozen*][freeze], not when they are applied.

`function transformer(node, file[, next])`

Transformers handle [*syntax tree*][syntax-tree]s and [*file*][file]s. A transformer is a function that is called each time a syntax tree and file are passed through the [*run phase*][description]. If an error occurs (either because it’s thrown, returned, rejected, or passed to [next][next]), the process stops.

The *run phase* is handled by [trough][trough], see its documentation for the exact semantics of these functions.

Parameters

node ([Node][node]) — [*Syntax tree*][syntax-tree] to handle
file ([VFile][vfile]) — [*File*][file] to handle
next ([Function][next], optional)

Returns

void — If nothing is returned, the next transformer keeps using same tree.
Error — Fatal error to stop the process
node ([Node][node]) — New [*syntax tree*][syntax-tree]. If returned, the next transformer is given this new tree
Promise — Returned to perform an asynchronous operation. The promise must be resolved (optionally with a [Node][node]) or rejected (optionally with an Error)

`function next(err[, tree[, file]])`

If the signature of a [*transformer*][transformer] includes next (the third argument), the transformer may perform asynchronous operations, and must call next().

Parameters

err (Error, optional) — Fatal error to stop the process
node ([Node][node], optional) — New [*syntax tree*][syntax-tree]. If given, the next transformer is given this new tree
file ([VFile][vfile], optional) — New [*file*][file]. If given, the next transformer is given this new file

`Preset`

Presets are sharable [*configuration*][configuration]. They can contain [*plugins*][plugin] and settings.

Example

preset.js:

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:

markdown
# Hello, world!

_Emphasis_ and **importance**.

## Table of contents

## API

## License

index.js:

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:

txt
readme.md: no issues found

readme.md now contains:

markdown
# Hello, world!

*Emphasis* and **importance**.

## Table of contents

*   [API](#api)
*   [License](#license)

## API

## License

[MIT](license) © [Titus Wormer](https://wooorm.com)

Contribute

See [contributing.md][contributing] in [unifiedjs/.github][health] for ways to get started. See [support.md][support] for ways to get help. Ideas for new plugins and tools can be posted in [unifiedjs/ideas][ideas].

A curated list of awesome unified resources can be found in [awesome unified][awesome].

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

Acknowledgments

Preliminary work for unified was done [in 2014][preliminary] for [retext][retext] and inspired by [ware][ware]. Further incubation happened in [remark][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][trough], thanks to **@calvinfo**, **@ianstormtaylor**, and others for their work on [ware][ware], as it was a huge initial inspiration.