@x-govuk/govuk-eleventy-plugin/src/collections/tags.js

Write documentation using Markdown and publish it using GOV.UK styles

export const tags = (collection) => {
  const items = collection.getAll()
  let tags = []

  for (const item of items) {
    if ('tags' in item.data) {
      // Add any new tags from the post to the array
      for (const tag of item.data.tags) {
        // Skip if tag already added
        if (!tags.includes(tag)) {
          // Check there’s not a matching tag, except for capitalisation
          const existingTag = tags.find(
            (existingTag) => existingTag.toLowerCase() === tag.toLowerCase()
          )
          if (existingTag) {
            throw new Error(
              `The post ‘${item.data.title}’ contains tag ‘${tag}’ which matches ‘${existingTag}’, but the capitalisation is different.`
            )
          }

          // Otherwise add new tag
          tags.push(tag)
        }
      }
    }
  }

  // Sort tags alphabetically
  tags = tags.sort((a, b) => a.localeCompare(b, 'en'))

  return tags
}