A Metalsmith plugin to read file metadata from frontmatter. Supports all frontmatter formats supported by the gray-matter library (including YAML, JSON, TOML, CSON, and more).

"But wait!" you say. "Doesn't Metalsmith already have frontmatter parsing built-in"? Well, yes. For now anyway. This plugin is an attempt to extract that functionality out of the Metalsmith core. Eventually the goal is to have frontmatter parsing removed from the Metalsmith core entirely in favor of this plugin or a similar one (see segmentio/metalsmith#157).

Even in the absence of that change though, this plugin has several key advantages over the built-in frontmatter parsing in Metalsmith. Firstly, it's composable with other plugins. For example, you could use it with metalsmith-branch to turn on frontmatter parsing for only a subset of files, or you could place it after metalsmith-s3 in the plugin list so that it parses frontmatter in downloaded files.

Secondly, this plugin provides a way to pass options to the underlying frontmatter parsing library, gray-matter. This allows you to do things like change the delimiter used to separate frontmatter from the rest of the file, or set TOML as the default frontmatter format.

Thirdly, this plugin provides an additional feature allowing parsed frontmatter to be automatically namespaced under a single key (e.g. page.keys instead of keys).

These are all things you can't do with Metalsmith's built-in frontmatter parsing.

npm install --save metalsmith-matters

After installing metalsmith-matters, simply add the metalsmith-matters key to the plugins in your metalsmith.json file. Be sure to include it before any plugins which need to use the metadata in your frontmatter, or which expect as input files with no frontmatter header. Generally speaking, this means that metalsmith-matters should be the first plugin in the list.

{
  "frontmatter": false, // Disable built-in frontmatter parsing (recommended)
  "plugins": {
    "metalsmith-matters": {
      // Options
    }
    // Other plugins...
  }
}

After installing metalsmith-matters, you can require metalsmith-matters in your code, then call the exported value to initialize the plugin and pass the result to Metalsmith.use (just as you would with any other Metalsmith plugin). Again, be sure to use metalsmith-matters before any plugins which need to use the metadata defined your frontmatter, or which expect as input files with no frontmatter header. Generally speaking, this means that metalsmith-matters should be the first plugin in the list.

var frontmatter = require('metalsmith-matters');

Metalsmith(__dirname)
  .frontmatter(false) // Disable built-in frontmatter parsing (recommended)
  .use(frontmatter({
    // Options
  }))
  .use(/* Other plugins... */)
  .build(function(err) {
    if (err) throw err;
  });

Type: string
Default: undefined

Namespace all parsed data under a single key.

Your frontmatter:

---
title: My title
author: Joe Writer
---

In the JavaScript:

  // new Metalsmith…
  .use(frontmatter({ namespace: 'page' }))
  // …build()

Now in your HTML, you can access the metadata like this (example with Handlebars):

  <h1>{{ page.title }}</h1>
  <p>Author: {{ page.author }}</p>

metalsmith-matters also supports all the options supported by gray-matter, metalsmith-matters' underlying frontmatter parsing library (it's the same one used by the Metalsmith core). These include:

• parser
• eval
• lang
• delims

For details on how to use these options, see the documentation for gray-matter.