# remark-lint-no-undefined-references
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[`remark-lint`][github-remark-lint] rule to warn when undefined definitions are referenced.
## Contents
* [What is this?](#what-is-this)
* [When should I use this?](#when-should-i-use-this)
* [Presets](#presets)
* [Install](#install)
* [Use](#use)
* [API](#api)
* [`unified().use(remarkLintNoUndefinedReferences[, options])`](#unifieduseremarklintnoundefinedreferences-options)
* [`Options`](#options)
* [Recommendation](#recommendation)
* [Examples](#examples)
* [Compatibility](#compatibility)
* [Contribute](#contribute)
* [License](#license)
## What is this?
This package checks that referenced definitions are defined.
## When should I use this?
You can use this package to check for broken references.
## Presets
This plugin is included in the following presets:
| Preset | Options |
| - | - |
| [`remark-preset-lint-recommended`](https://github.com/remarkjs/remark-lint/tree/main/packages/remark-preset-lint-recommended) | |
## Install
This package is [ESM only][github-gist-esm].
In Node.js (version 16+),
install with [npm][npm-install]:
```sh
npm install remark-lint-no-undefined-references
```
In Deno with [`esm.sh`][esm-sh]:
```js
import remarkLintNoUndefinedReferences from 'https://esm.sh/remark-lint-no-undefined-references@5'
```
In browsers with [`esm.sh`][esm-sh]:
```html
```
## Use
On the API:
```js
import remarkLint from 'remark-lint'
import remarkLintNoUndefinedReferences from 'remark-lint-no-undefined-references'
import remarkParse from 'remark-parse'
import remarkStringify from 'remark-stringify'
import {read} from 'to-vfile'
import {unified} from 'unified'
import {reporter} from 'vfile-reporter'
const file = await read('example.md')
await unified()
.use(remarkParse)
.use(remarkLint)
.use(remarkLintNoUndefinedReferences)
.use(remarkStringify)
.process(file)
console.error(reporter(file))
```
On the CLI:
```sh
remark --frail --use remark-lint --use remark-lint-no-undefined-references .
```
On the CLI in a config file (here a `package.json`):
```diff
…
"remarkConfig": {
"plugins": [
…
"remark-lint",
+ "remark-lint-no-undefined-references",
…
]
}
…
```
## API
This package exports no identifiers.
It exports the [TypeScript][typescript] type
[`Options`][api-options].
The default export is
[`remarkLintNoUndefinedReferences`][api-remark-lint-no-undefined-references].
### `unified().use(remarkLintNoUndefinedReferences[, options])`
Warn when undefined definitions are referenced.
###### Parameters
* `options` ([`Options`][api-options], optional)
— configuration
###### Returns
Transform ([`Transformer` from `unified`][github-unified-transformer]).
### `Options`
Configuration (TypeScript type).
###### Fields
* `allow` (`Array`, optional)
— list of values to allow between `[` and `]`
* `allowShortcutLink` (`boolean`, default: `false`)
— allow shortcut references, which are just brackets such as `[text]`
## Recommendation
Shortcut references use an implicit syntax that could also occur as plain
text.
To illustrate,
it is reasonable to expect an author adding `[…]` to abbreviate some text
somewhere in a document:
```markdown
> Some […] quote.
```
This isn’t a problem,
but it might become one when an author later adds a definition:
```markdown
Some new text […][].
[…]: #read-more
```
The second author might expect only their newly added text to form a link,
but their changes also result in a link for the text by the first author.
## Examples
##### `ok.md`
###### In
```markdown
[Mercury][] is the first planet from the Sun and the smallest in the Solar
System.
Venus is the second planet from the [Sun.
Earth is the third planet from the \[Sun] and the only astronomical object
known to harbor life\.
Mars is the fourth planet from the Sun: [].
[mercury]: https://example.com/mercury/
```
###### Out
No messages.
##### `not-ok.md`
###### In
```markdown
[Mercury] is the first planet from the Sun and the smallest in the Solar
System.
[Venus][] is the second planet from the Sun.
[Earth][earth] is the third planet from the Sun and the only astronomical
object known to harbor life.
![Mars] is the fourth planet from the Sun in the [Solar
System].
> Jupiter is the fifth planet from the Sun and the largest in the [Solar
> System][].
[Saturn][ is the sixth planet from the Sun and the second-largest
in the Solar System, after Jupiter.
[*Uranus*][] is the seventh planet from the Sun.
[Neptune][neptune][more] is the eighth and farthest planet from the Sun.
```
###### Out
```text
1:1-1:10: Unexpected reference to undefined definition, expected corresponding definition (`mercury`) for a link or escaped opening bracket (`\[`) for regular text
4:1-4:10: Unexpected reference to undefined definition, expected corresponding definition (`venus`) for a link or escaped opening bracket (`\[`) for regular text
6:1-6:15: Unexpected reference to undefined definition, expected corresponding definition (`earth`) for a link or escaped opening bracket (`\[`) for regular text
9:2-9:8: Unexpected reference to undefined definition, expected corresponding definition (`mars`) for an image or escaped opening bracket (`\[`) for regular text
9:50-10:8: Unexpected reference to undefined definition, expected corresponding definition (`solar system`) for a link or escaped opening bracket (`\[`) for regular text
12:67-13:12: Unexpected reference to undefined definition, expected corresponding definition (`solar > system`) for a link or escaped opening bracket (`\[`) for regular text
15:1-15:9: Unexpected reference to undefined definition, expected corresponding definition (`saturn`) for a link or escaped opening bracket (`\[`) for regular text
18:1-18:13: Unexpected reference to undefined definition, expected corresponding definition (`*uranus*`) for a link or escaped opening bracket (`\[`) for regular text
20:1-20:19: Unexpected reference to undefined definition, expected corresponding definition (`neptune`) for a link or escaped opening bracket (`\[`) for regular text
20:19-20:25: Unexpected reference to undefined definition, expected corresponding definition (`more`) for a link or escaped opening bracket (`\[`) for regular text
```
##### `ok-allow.md`
When configured with `{ allow: [ '…' ] }`.
###### In
```markdown
Mercury is the first planet from the Sun and the smallest in the Solar
System. […]
```
###### Out
No messages.
##### `source.md`
When configured with `{ allow: [ { source: '^mer' }, 'venus' ] }`.
###### In
```markdown
[Mercury][] is the first planet from the Sun and the smallest in the Solar
System.
[Venus][] is the second planet from the Sun.
```
###### Out
No messages.
##### `gfm.md`
###### In
> 👉 **Note**: this example uses
> GFM ([`remark-gfm`][github-remark-gfm]).
```markdown
Mercury[^mercury] is the first planet from the Sun and the smallest in the
Solar System.
[^venus]:
**Venus** is the second planet from the Sun.
```
###### Out
```text
1:8-1:18: Unexpected reference to undefined definition, expected corresponding definition (`mercury`) for a footnote or escaped opening bracket (`\[`) for regular text
```
##### `allow-shortcut-link.md`
When configured with `{ allowShortcutLink: true }`.
###### In
```markdown
[Mercury] is the first planet from the Sun and the smallest in the Solar
System.
[Venus][] is the second planet from the Sun.
[Earth][earth] is the third planet from the Sun and the only astronomical object
known to harbor life.
```
###### Out
```text
4:1-4:10: Unexpected reference to undefined definition, expected corresponding definition (`venus`) for a link or escaped opening bracket (`\[`) for regular text
6:1-6:15: Unexpected reference to undefined definition, expected corresponding definition (`earth`) for a link or escaped opening bracket (`\[`) for regular text
```
## 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,
`remark-lint-no-undefined-references@5`,
compatible with Node.js 16.
## Contribute
See [`contributing.md`][github-dotfiles-contributing] in [`remarkjs/.github`][github-dotfiles-health] for ways
to get started.
See [`support.md`][github-dotfiles-support] for ways to get help.
This project has a [code of conduct][github-dotfiles-coc].
By interacting with this repository, organization, or community you agree to
abide by its terms.
## License
[MIT][file-license] © [Titus Wormer][author]
[api-options]: #options
[api-remark-lint-no-undefined-references]: #unifieduseremarklintnoundefinedreferences-options
[author]: https://wooorm.com
[badge-build-image]: https://github.com/remarkjs/remark-lint/workflows/main/badge.svg
[badge-build-url]: https://github.com/remarkjs/remark-lint/actions
[badge-chat-image]: https://img.shields.io/badge/chat-discussions-success.svg
[badge-chat-url]: https://github.com/remarkjs/remark/discussions
[badge-coverage-image]: https://img.shields.io/codecov/c/github/remarkjs/remark-lint.svg
[badge-coverage-url]: https://codecov.io/github/remarkjs/remark-lint
[badge-downloads-image]: https://img.shields.io/npm/dm/remark-lint-no-undefined-references.svg
[badge-downloads-url]: https://www.npmjs.com/package/remark-lint-no-undefined-references
[badge-funding-backers-image]: https://opencollective.com/unified/backers/badge.svg
[badge-funding-sponsors-image]: https://opencollective.com/unified/sponsors/badge.svg
[badge-funding-url]: https://opencollective.com/unified
[badge-size-image]: https://img.shields.io/bundlejs/size/remark-lint-no-undefined-references
[badge-size-url]: https://bundlejs.com/?q=remark-lint-no-undefined-references
[esm-sh]: https://esm.sh
[file-license]: https://github.com/remarkjs/remark-lint/blob/main/license
[github-dotfiles-coc]: https://github.com/remarkjs/.github/blob/main/code-of-conduct.md
[github-dotfiles-contributing]: https://github.com/remarkjs/.github/blob/main/contributing.md
[github-dotfiles-health]: https://github.com/remarkjs/.github
[github-dotfiles-support]: https://github.com/remarkjs/.github/blob/main/support.md
[github-gist-esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
[github-remark-gfm]: https://github.com/remarkjs/remark-gfm
[github-remark-lint]: https://github.com/remarkjs/remark-lint
[github-unified-transformer]: https://github.com/unifiedjs/unified#transformer
[npm-install]: https://docs.npmjs.com/cli/install
[typescript]: https://www.typescriptlang.org
.