How to access frontmatter data (as title, author...) from a plugin ?

[Welsh44]

Hi

I discovered Marp few weeks ago and found it very convenient.
I began with Windows binaries but went to npx marp-cli in order to use plugins.

As I 'm working on template for my company, I'd like to implement a canvas.
In order to this, I'd like to access via a plugin.
I found an example here : https://github.com/orgs/marp-team/discussions/510#discussioncomment-9397590
But I didn't find how to extend this code whith access to frontmatter "native" data as author, title, header, footer...

Thanks in advance for any clue.

[yhatt]

As mentioned at https://marpit.marp.app/directives and https://github.com/orgs/marp-team/discussions/510#discussioncomment-9397590, Marpit framework will store parsed directives, including defined in the front-matter, as the metadata of each slide token: marpitDirectives. You can inject the parser rule of markdown-it to read the metadata at after parsing directives.

// engine.mjs
const yourPlugin = (md) => {
  md.core.ruler.after(
    'marpit_directives_apply',
    'your_custom_rule', // Rename the rule as you like
    (state) => {
      if (state.inlineMode) return

      for (const token of state.tokens) {
        if (
          typeof token.meta?.marpitSlide === 'number' &&
          typeof token.meta.marpitDirectives === 'object'
        ) {
          // Peak the metadata of directives for debug
          console.log(
            token.meta?.marpitSlide, // Slide page index (0-based)
            '=>',
            token.meta.marpitDirectives // Directives of the slide
          )

          // ... and you can do anything with using the value of directives ...
        }
      }
    }
  )
}

export default ({ marp }) => marp.use(yourPlugin)

---
title: Title
author: Author
header: '**Header**'
footer: '_Footer_'
---

# Title

---

<!-- footer: Footer changed -->

Hello!

$ marp --engine ./engine.mjs ./markdown.md
[  INFO ] Converting 1 markdown...
0 => {
  header: '**Header**',
  footer: '_Footer_',
  marpCLITitle: 'Title',
  marpCLIAuthor: 'Author'
}
1 => {
  header: '**Header**',
  footer: 'Footer changed',
  marpCLITitle: 'Title',
  marpCLIAuthor: 'Author'
}
[  INFO ] markdown.md => markdown.html

Note

The name of directive and the identifier of metadata may become different, for a reason of the purpose to avoid conflict identifiers with other plugins. Some of well-known global directives such as author and title are the additional directives extended by Marp CLI, so they have marpCLI prefixed identifiers. (Code)

[Welsh44]

Thank you.
I followed the links you mentionned but I didn't understand or wasn't aware of token.meta?.marpitSlide.