Linked Headings

Create anchor-linked headings in MDX.

Use remark-slug with MDX to create IDs based on the heading’s content. If you’re using Gatsby, add this to your gatsby-plugin-mdx options.

gatsby-config.js

const remarkSlug = require('remark-slug')

module.exports = {
  plugins: [
    {
      resolve: 'gatsby-plugin-mdx',
      options: {
        remarkPlugins: [remarkSlug],
      },
    },
  ],
}

If you’re using Contentlayer, you can use the remarkSlug plugin in your contentlayer.config.js file.

contentlayer.config.js

import { defineDocumentType, makeSource } from 'contentlayer/source-files'
import remarkSlug from 'remark-slug'

export const Post = defineDocumentType(() => ({
  name: 'Post',
  filePathPattern: '*.mdx',
  contentType: 'mdx',
  fields: {},
}))

export default makeSource({
  contentDirPath: 'posts',
  documentTypes: [Post],
  mdx: {
    remarkPlugins: [remarkSlug],
    rehypePlugins: [],
  },
})

Next, create a components module to pass to MDX context. If you’re using gatsby-plugin-theme-ui, add a src/gatsby-plugin-theme-ui/components.js file. If you’re not using Gatsby, pass these components to the MDXProvider component.

src/gatsby-plugin-theme-ui/components.js

/** @jsxImportSource theme-ui */

const heading = (Tag) => (props) => {
  if (!props.id) return <Tag {...props} />

  return (
    <Tag {...props}>
      <a href={`#${props.id}`}>{props.children}</a>
    </Tag>
  )
}

const components = {
  h1: heading('h1'),
  h2: heading('h2'),
  h3: heading('h3'),
  h4: heading('h4'),
  h5: heading('h5'),
  h6: heading('h6'),
}

export default components

Or with TypeScript:

components.tsx

import type { ComponentPropsWithoutRef } from 'react'
import { Themed } from '@theme-ui/mdx'

const createHeadingWithLink =
  (Level: 'h2' | 'h3' | 'h4' | 'h5' | 'h6') =>
  (props: ComponentPropsWithoutRef<'h2'>) =>
    (
      <Level {...props}>
        {props.id && (
          <a
            href={`#${props.id}`}
            sx={{
              color: 'inherit',
              textDecoration: 'none',
              ':hover': {
                textDecoration: 'underline',
              },
            }}
          >
            {props.children}
          </a>
        )}
      </Level>
    )

export const components = {
  h2: createHeadingWithLink('h2'),
  h3: createHeadingWithLink('h3'),
  h4: createHeadingWithLink('h4'),
  h5: createHeadingWithLink('h5'),
  h6: createHeadingWithLink('h6'),
}

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Components