@metalsmith/collections

A Metalsmith plugin that lets you group files together into ordered collections, like blog posts. That way you can loop over them to generate index pages, add 'next' and 'previous' links between them, and more

Features

• can match files by collection file metadata
• can match files by pattern
• can limit the number of files in a collection
• can filter files in a collection based on file metadata
• adds collections to global metadata
• adds next and previous references to each file in the collection

Installation

NPM:

npm install @metalsmith/collections

Yarn:

yarn add @metalsmith/collections

Usage

Pass options to @metalsmith/collections in the plugin chain:

import Metalsmith from 'metalsmith'
import markdown from '@metalsmith/markdown'
import collections from '@metalsmith/collections'
import { dirname } from 'path'

const __dirname = dirname(new URL(import.meta.url).pathname)

// defaults, only create collections based on file metadata
Metalsmith(__dirname)
  .use(markdown())
  .use(collections())

// defaults for a "news" collection, except pattern option
Metalsmith(__dirname)
  .use(markdown())
  .use(collections({
    news: { pattern: 'news/**/*.html' }
  }))

// explicit defaults for a "news" collection, except pattern option
Metalsmith(__dirname)
  .use(markdown())
  .use(collections({
    pattern: { pattern: 'news/**/*.html' },
    metadata: null,
    filterBy: () => true,
    sortBy: defaultSort,
    reverse: false,
    limit: Infinity,
    refer: true
  })

Note: all examples in the readme use the same collections definitions under Defining collections

Options

All options are optional

• pattern string|string[] - one or more glob patterns to group files into a collection
• filterBy Function - a function that returns false for files that should be filtered out of the collection
• limit number - restrict the number of files in a collection to at most limit
• sortBy string|Function - a file metadata key to sort by (for example date or pubdate or title), or a custom sort function
• reverse boolean - whether the sort should be reversed (e.g., for a news/blog collection, you typically want reverse: true)
• metadata Object|string - metadata to attach to the collection. Will be available as metalsmith.metadata().collections.<name>.metadata. This can be used for example to attach metadata for index pages. If a string is passed, it will be interpreted as a file path to an external JSON or YAML metadata file
• refer boolean - will add previous and next keys to each file in a collection. true by default

Defining collections

There are 2 ways to create collections & they can be used together:

• by pattern - for example, this is how you would create multiple pattern-based collections, based on the folders photos, news, and services:

  metalsmith.use(
    collections({
      gallery: 'photos/**/*.{jpg,png}',
      news: {
        metadata: {
          title: 'Latest news',
          description: 'All the latest in politics & world news',
          slug: 'news'
        },
        pattern: 'news/**/*.html',
        sortBy: 'pubdate',
        reverse: true
      },
      services: 'services/**/*.html'
    })
  )

• by file metadata - add a collection property to the front-matter of each file that you want to add to a collection. The markdown file below will be included in the news collection even if it's not in the news folder (see previous example)

  something-happened.md

  ---
  title: Something happened
  collection: news
  pubdate: 2021-12-01
  layout: news.hbs
  ---
  
  ...contents

  Note that you can also add the same file to multiple collections, which is useful for example if you want to use @metalsmith/collections as a category system:

  something-happened.md

  title: Something happened
  collection:
  
  - news
  - category_politics
  - category_world
    pubdate: 2021-12-01
    layout: news.hbs
  
  ---
  
  ...contents

Rendering collection items

Here is an example of using @metalsmith/layouts with jstransformer-handlebars to render the something-happened.md news item, with links to the next and previous news items (using refer: true options):

layouts/news.njk

<h1>{{ title }}</h1> {{!-- something-happened.md title --}}
<a href="/{{ collections.news.metadata.slug }}">Back to news</a> {{!-- news collection metadata.slug --}}
{{ contents | safe }}
<hr>
{{!-- previous & next are added by @metalsmith/collections --}}
{{#if previous}}
Read the previous news:
<a href="/{{ previous.path }}">{{ previous.title }}</a>
{{/if}}
{{#if next}}
Read the next news:
<a href="/{{ next.path }}">{{ next.title }}</a>
{{/if}}

Note: If you don't need the next and previous references, you can pass the option refer: false

Rendering collection index

All matched files are added to an array that is exposed as a key of metalsmith global metadata, for example the news collection would be accessible at Metalsmith.metadata().collections.news . Below is an example of how you could render an index page for the news collection:

layouts/news-index.hbs

<h1>{{ title }}</h1> {{!-- news collection metadata.title --}}
<p>{{ description }}</p> {{!-- news collection metadata.description --}}
<hr>
{{!-- previous & next are added by @metalsmith/collections --}}
{{#if collections.news.length }}
  <ul>
  {{#each collections.news}}
    <li>
      <h3><a href="/{{path}}">{{ title }}</a></h3>
      <p>{{ excerpt }}</p>
    </li>
  {{/each}}
  </ul>
{{/each}}
{{else}}
No news at the moment...
{{/if}}

Custom sorting, filtering and limiting

You could define an order property on a set of files and pass sortBy: "order" to @metalsmith/collections for example, or you could override the sort with a custom function (for example to do multi-level sorting). For instance, this function sorts the "subpages" collection by a numerical "index" property but places unindexed items last.

metalsmith.use(
  collections({
    subpages: {
      sortBy: function (a, b) {
        let aNum, bNum

        aNum = +a.index
        bNum = +b.index

        // Test for NaN
        if (aNum != aNum && bNum != bNum) return 0
        if (aNum != aNum) return 1
        if (bNum != bNum) return -1

        // Normal comparison, want lower numbers first
        if (aNum > bNum) return 1
        if (bNum > aNum) return -1
        return 0
      }
    }
  })
)

Note: the sortBy option also understands nested keypaths, e.g. display.order

The filterBy function is passed a single argument which corresponds to each file's metadata. You can use the metadata to perform comparisons or carry out other decision-making logic. If the function you supply evaluates to true, the file will be added to the collection. If it evaluates to false, the file will not be added. The filterBy function below could work for a collection named thisYearsNews as it would filter out all the items that are older than this year:

function filterBy(file) {
  const today = new Date()
  const pubdate = new Date(file.pubdate)
  return pubdate.getFullYear() === today.getFullYear()
}

Add a limit option to a collection config, for example to separate recent articles from archives:

metalsmith.use(
  collections({
    recentArticles: {
      pattern: 'articles/**/*.html',
      sortBy: 'date',
      limit: 10
    },
    archives: {
      pattern: 'archives/**/*.html',
      sortBy: 'date'
    }
  })
)

Note: the collection is first sorted, reversed, filtered, and then limited, if applicable.

Collection Metadata

Additional metadata can be added to the collection object:

metalsmith.use(
  collections({
    news: {
      metadata: {
        title: 'Latest news',
        description: 'All the latest in politics & world news',
        slug: 'news'
      }
    }
  })
)

Collection metadata can be loaded from a json or yaml file (path relative to Metalsmith.directory()):

metalsmith.use(
  collections({
    articles: {
      sortBy: 'date',
      reverse: true,
      metadata: 'path/to/file.json'
    }
  })
)

Debug

To log debug output, set the DEBUG environment variable to @metalsmith/collections:

Linux/Mac:

DEBUG=@metalsmith/collections

Windows:

set "DEBUG=@metalsmith/collections"

CLI Usage

Add the @metalsmith/collections key to your metalsmith.json plugins key:

{
  "plugins": [
    {
      "@metalsmith/collections": {
        "articles": {
          "sortBy": "date",
          "reverse": true
        }
      }
    }
  ]
}

License

MIT