remark-lint-no-duplicate-headings

remark-lint-no-duplicate-headings

remark-lint rule to warn when the same text is used in multiple headings.

Contents

• What is this?
• When should I use this?
• Presets
• Install
• Use
• API
  • unified().use(remarkLintNoDuplicateHeadings)
• Recommendation
• Examples
• Compatibility
• Contribute
• License

What is this?

This package checks that headings are unique.

When should I use this?

You can use this package to check that headings are unique.

Presets

This plugin is included in the following presets:

Preset	Options
remark-preset-lint-markdown-style-guide

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install remark-lint-no-duplicate-headings

In Deno with esm.sh:

import remarkLintNoDuplicateHeadings from 'https://esm.sh/remark-lint-no-duplicate-headings@4'

In browsers with esm.sh:

<script type="module">
  import remarkLintNoDuplicateHeadings from 'https://esm.sh/remark-lint-no-duplicate-headings@4?bundle'
</script>

Use

On the API:

import remarkLint from 'remark-lint'
import remarkLintNoDuplicateHeadings from 'remark-lint-no-duplicate-headings'
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(remarkLintNoDuplicateHeadings)
  .use(remarkStringify)
  .process(file)

console.error(reporter(file))

On the CLI:

remark --frail --use remark-lint --use remark-lint-no-duplicate-headings .

On the CLI in a config file (here a package.json):

 …
 "remarkConfig": {
   "plugins": [
     …
     "remark-lint",
+    "remark-lint-no-duplicate-headings",
     …
   ]
 }
 …

API

This package exports no identifiers. It exports no additional TypeScript types. The default export is remarkLintNoDuplicateHeadings.

unified().use(remarkLintNoDuplicateHeadings)

Warn when the same text is used in multiple headings.

Parameters

There are no options.

Returns

Transform (Transformer from unified).

Recommendation

Headings having unique text helps screen reader users, who typically use “jump to heading” features to navigate within a page, which reads headings out loud.

It also helps because often headings receive automatic unique IDs, and when the same heading text is used, they are suffixed with a number based on where they are positioned in the document, which makes linking to them prone to changes.

Examples

ok.md

In

# Mercury

## Venus

Out

No messages.

not-ok.md

In

# Mercury

## Mercury

## [Mercury](http://example.com/mercury/)

Out

3:1-3:11: Unexpected heading with equivalent text, expected unique headings
5:1-5:42: Unexpected heading with equivalent text, expected unique headings

mdx.mdx

In

👉 Note: this example uses MDX (remark-mdx).

<h1>Mercury</h1>
<h2>Mercury</h2>

Out

2:1-2:17: Unexpected heading with equivalent text, expected unique headings

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-duplicate-headings@4, compatible with Node.js 16.

Contribute

See contributing.md in remarkjs/.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.

License

MIT © Titus Wormer