Dimer markdown

Opinionated markdown parser built on top of Remark.js

Dimer markdown is an opinionated markdown processor built on top of remark with the following features and goals.

Note: This package is ESM only

• Generates HAST abstract syntax tree as the output. Later, you can use any template engine or a frontend framework to render HTML from the AST.
• Implements the markdown directives proposal to extend the markdown native capabilities.
• Introduces the concept of macros that builds up on top of directives.
• Selectively allow/dis-allow HTML inside Markdown.
• Register listeners to hook into the Markdown compilation phase.
• Ships with first-class support for parsing frontmatter.
• Automatically generates the toc for the markdown headings.
• Support for line highlights in code blocks.
• Pre-built macros to render code group tabs, embed videos, and show alert messages.

Setup

Install the package from the npm registry as follows:

npm i @dimerapp/markdown

# yarn
yarn add @dimerapp/markdown

And import the package to process the markdown files.

import { MarkdownFile } from '@dimerapp/markdown'

const markdownContents = `
# Hello world

This is a markdown doc with GFM syntax.

- [ ] Todo 1
- [ ] Todo 2`

const md = new MarkdownFile(markdownContents)
const ast = await md.process()

Generating HTML

We encourage you to render the AST to HTML using some template engine or a frontend framework like Vue or React to have better control over the rendered HTML.

However, if you want to keep things simple, you can use the following toHTML utility function to render HTML from AST.

import { MarkdownFile } from '@dimerapp/markdown'
import { toHtml } from '@dimerapp/markdown/utils'

const md = new MarkdownFile(contents)
await md.process()

const { contents, summary, toc, excerpt } = toHTML(md)
if (summary) {
  // render summary html
}

if (toc) {
  // render TOC html
}

if (excerpt) {
  // render excerpt text
}

// render content html

• contents is the HTML representation of the markdown file contents.
• summary is the HTML representation of the file summary. The summary HTML only exists when you have defined it inside the markdown content frontmatter.
• toc is the HTML representation of the table of contents. Available only when generateToc is set to true.
• excerpt is the plain text version of the summary. Available only when the summary is defined in the front matter.

Options

You can pass the following options when creating a new instance of the MarkdownFile.

import { MarkdownFile } from '@dimerapp/markdown'

const md = new MarkdownFile(contents, {
  generateToc?: boolean
  allowHtml?: boolean
  filePath?: string
  enableDirectives?: boolean
})

• generateToc: Define whether you want to generate the table of contents or not. Defaults to false.
• allowHtml: Control whether you want to allow HTML inside Markdown or not. Defaults to false.
• filePath: Optionally, you can attach the absolute file path to the mdFile instance.
• enableDirectives: Enable support for the directives proposal. Defaults to false.

Directives and macros

Dimer markdown ships with an implementation of Markdown directives to enhance the markdown syntax by adding rich components inside it.

For example, using the following syntax, you can embed a Youtube video inside the markdown.

::youtube{id="Hm14pyibQhQ"}

By default, directives are converted to HTML tags. So, for example, the above youtube directive will be rendered as follows inside the HTML.

<youtube id="Hm14pyibQhQ"></youtube>

This is not helpful because there is no native youtube HTML element to embed youtube videos.

However, you can define a custom macro that receives the AST of the youtube directive, and then you can manipulate that AST to render a different HTML output. For example:

import { MarkdownFile } from '@dimerapp/markdown'
const md = new MarkdownFile(contents, { enableDirectives: true })

md.macro('youtube', function (node, file, removeNode) {
  node.data = node.data || {}

  /**
   * Create a div with classes "embed" and "embed-youtube"
   *
   * The properties are defined in the HAST syntax tree
   * format.
   * https://github.com/syntax-tree/hast
   */
  node.data.hName = 'div'
  node.data.hProperties = {
    className: ['embed', 'embed-youtube'],
  }

  const videoId = node.attributes.id
  const width = node.attributes.width
  const height = node.attributes.width

  /**
   * Add children nodes. We need an iframe and
   * the AST syntax tree must be in MDAST format.
   *
   * https://github.com/syntax-tree/mdast
   * https://github.com/syntax-tree/mdast-util-directive#syntax-tree
   */
  node.children = [
    {
      type: 'containerDirective',
      name: 'iframe',
      attributes: {
        src: `https://www.youtube.com/embed/${videoId}`,
        width: width || '100%',
        height: height || '400',
        frameborder: 'none',
        allow: 'autoplay; encrypted-media',
        allowfullscreen: 'true',
      },
      children: [],
    },
  ]
})

When you use the youtube directive, it will render the following HTML markup. So, the main goal of a macro is to take an AST node and mutate it.

<div class="embed embed-youtube">
  <iframe
    src="https://www.youtube.com/embed/Hm14pyibQhQ"
    width="100%"
    height="400"
    frameborder="none"
    allow="autoplay; encrypted-media"
    allowfullscreen
  >
  </iframe>
</div>

Macros props

You can access the props passed to a directive using the node.attributes property. For example:

:::container{flex=true columns=3}
:::

md.macro('container', function (node) {
  // { flex: 'true', columns: '3' }
  console.log(node.attributes)
})

Reporting errors from macros

Often, your macros will not receive the data it expects, so you would want to report errors to the markdown author.

You can report errors using the file.report method from within the macro.

md.macro('youtube', function (node, file, removeNode) {
  if (!node.attributes.id) {
    /**
     * Report error. Passing "node.position" is important
     * as it will allow us to report the error with the
     * exact line and column number.
     */
    file.report('"youtube" macro needs the youtube video id', node.position)

    /**
     * Remove the node from the markdown since we are
     * not able to handle it
     */
    removeNode()
    return
  }
})

Error messages

Every markdown file can have error messages associated with it. Usually, these errors are reported by the macros. However, you can report them manually as well.

import { MarkdownFile } from '@dimerapp/markdown'

const md = new MarkdownFile(contents)
await md.process()

if (!md.frontmatter.author) {
  md.report('Make sure to define the author for the markdown file')
}

for (let message of md.messages) {
  /**
   * Message is an instance of
   * https://www.npmjs.com/package/vfile-message
   */
  console.log(message)
}

Hooks

You can use hooks to observe or mutate the AST nodes as the markdown content is being processed.

The hook callback receives the AST syntax tree in MDAST format.

Warning Even though you can mutate the AST using hooks, we recommend not doing so and looking for alternative APIs. For example, you can use Macros to extend the markdown capabilities or use the rendering layer to render AST nodes differently.

In the following example, we will track all the to-do list items and keep a count of them.

import { mdastTypes } from '@dimerapp/markdown/types'
const md = new MarkdownFile(contents)

md.on('listItem', (node: mdastTypes.ListItem, file) => {
  /**
   * Not a todo list item
   */
  if (node.checked === null) {
    return
  }

  file.stats.todo = file.stats.todo || { total: 0, completed: 0 }
  file.stats.todo.total++

  if (node.checked === true) {
    file.stats.todo.completed++
  }
})

await md.process()

// Access stored todo stats
console.log(md.stats.todo)

Using remark plugins

You can use the remark-plugins by calling the transform method on the markdown file instance. The plugin API is the same as unified plugins.

import remarkCapitalize from 'remark-capitalize'

const md = new MarkdownFile(contents)
md.transform(remarkCapitalize)

await md.process()

Bundled macros

codegroup

Render multiple codeblocks inside a group of tabs. The macro wraps all the codeblocks inside a div with data-tabs property.

import { MarkdownFile } from '@dimerapp/markdown'
import { codegroup } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(codegroup)

:::codegroup

```ts
// title: Tab 1
```

```ts
// title: Tab 2
```

:::

Output AST

{
  tagName: 'div',
  properties: {
    dataTabs: '["Tab 1","Tab 2"]'
  }
  children: [/*Rest of the AST*/]
}

codesandbox

Embed a codesandbox example. All of the embed options can be passed as props.

import { MarkdownFile } from '@dimerapp/markdown'
import { codesandbox } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(codesandbox)

::codesandbox{url="https://codesandbox.io/s/github/adonisjs/adonis-starter-codesandbox/tree/master/?file=/server.js" autoresize=0 codemirror=1 fontsize=16}

note

Render an alert message of type note. The content of the directive is wrapped inside a div with alert alert-note class names.

import { MarkdownFile } from '@dimerapp/markdown'
import { note } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(note)

:::note
This is a note
:::

tip

Render an alert message of type tip. The content of the directive is wrapped inside a div with alert alert-tip class names.

import { MarkdownFile } from '@dimerapp/markdown'
import { tip } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(tip)

:::tip
This is a tip
:::

warning

Render an alert message of type warning. The content of the directive is wrapped inside a div with alert alert-warning class names.

import { MarkdownFile } from '@dimerapp/markdown'
import { warning } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(warning)

:::warning
This is a warning
:::

youtube

Embed a youtube video inside an iframe.

import { MarkdownFile } from '@dimerapp/markdown'
import { youtube } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(youtube)

::youtube{url="https://www.youtube.com/watch?v=Hm14pyibQhQ"}

Along with the URL, you can also pass the width and height of the video.

::youtube{url="https://www.youtube.com/watch?v=Hm14pyibQhQ" width="1280" height="720"}

video

Embed a video using the video HTML tag. The video tag is wrapped inside a div with embed embed-video class names.

import { MarkdownFile } from '@dimerapp/markdown'
import { video } from '@dimerapp/markdown/macros'

const md = new MarkdownFile(content)
md.use(video)

::video{url="./bunny.mp4"}

Along with the url, you can also pass the following props.

• autoplay
• controls
• loop
• preload
• poster

Enhanced markdown syntax

Github flavored markdown

The github flavored markdown is fully supported by default.

Auto linking headings

All of the headings inside the markdown receives a unique id based upon the heading content. Also, all headings receives a little bookmark link next to them.

Codeblock enhancements

Following is the AST node structure for the codeblock.

type CodeBlock = {
  type: 'code'
  lang: string
  meta: {
    title: null | string
    highlights: number[]
    inserts: number[]
    deletes: number[]
  }
}

• lang: The language is defined by writing the language abbreviation after the three backticks. In the following example, ts is the abbreviation for TypeScript.

  ```ts
  ```
  

• meta.title: The codeblock title defined using the // title comment.
• meta.highlights: An array of line numbers for the lines to be highlighted.
• meta.inserts: An array of line numbers to be highlighted as diff inserts.
• meta.deletes: An array of line numbers to be highlighted as diff deletes.

Codeblock title

You can define the title for a codeblock by adding a comment in the first line.

// title: Routes file
Route.get('/', () => {})

The title will end up on the meta object of the codeblock AST node.

Codeblock line highlights

You can highlight lines within the codeblocks using the highlight-start and highlight-end comments.

// highlight-start
This line is highlighted
// highlight-end

Codeblock line diffs

You can show add and remove line diffs using the insert-start and delete-start comments.

// delete-start
var foo = 'bar'
// delete-end
// insert-start
const foo = 'bar'
// insert-end