vue-markdown

Vue component to render markdown.

Feature highlights

• [x] safe by default (no dangerouslySetInnerHTML or XSS attacks)
• [x] components (pass your own component to use instead of <h2> for ## hi)
• [x] plugins (many plugins you can pick and choose from)
• [x] compliant (100% to CommonMark, 100% to GFM with a plugin)

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • Markdown
  • MarkdownHooks
  • defaultUrlTransform(url)
  • AllowElement
  • Components
  • ExtraProps
  • HooksOptions
  • Options
  • UrlTransform
• Examples
  • Use a plugin
  • Use a plugin with options
  • Use custom components (syntax highlight)
  • Use remark and rehype plugins (math)
• Plugins
• Syntax
• Compatibility
• Architecture
• Appendix A: HTML in markdown
• Appendix B: Components
• Appendix C: line endings in markdown (and JSX)
• Security
• Related
• Contribute
• License

What is this?

This package is a Vue component that can be given a string of markdown that it’ll safely render to Vue elements. You can pass plugins to change how markdown is transformed and pass components that will be used instead of normal HTML elements.

• to learn markdown, see this cheatsheet and tutorial

When should I use this?

There are other ways to use markdown in Vue out there so why use this one? The three main reasons are that they often rely on dangerouslySetInnerHTML, have bugs with how they handle markdown, or don’t let you swap elements for components. vue-markdown builds a virtual DOM, so Vue only replaces what changed, from a syntax tree. That’s supported because we use unified, specifically remark for markdown and rehype for HTML, which are popular tools to transform content with plugins.

This package focusses on making it easy for beginners to safely use markdown in Vue.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install @ghbsom/vue-markdown

Use

A basic hello world:

<template>
  <Markdown :text="markdown" />
</template>

<script setup>
  import {ref} from 'vue';
  import Markdown from '@ghbsom/vue-markdown'
  const markdown = ref('# Hi, *Pluto*!');
</script>

<h1>
  Hi, <em>Pluto</em>!
</h1>

Here is an example that shows how to use a plugin (remark-gfm, which adds support for footnotes, strikethrough, tables, tasklists and URLs directly):

<template>
  <Markdown :text="markdown" :remarkPlugins="[remarkGfm]"/>
</template>

<script setup>
  import {ref} from 'vue';
  import remarkGfm from 'remark-gfm'
  import Markdown from '@ghbsom/vue-markdown'
  const markdown = ref('Just a link: www.nasa.gov.')
</script>

<p>
  Just a link: <a href="http://www.nasa.gov">www.nasa.gov</a>.
</p>

API

This package exports the identifiers MarkdownHooks, and defaultUrlTransform. The default export is Markdown.

Markdown

Component to render markdown.

This is a synchronous component. When using async plugins, see MarkdownHooks.

Parameters

• options (Options) — props

Returns

Vue element

MarkdownHooks

Component to render markdown with support for async plugins through hooks.

This Component run on the client and do not immediately render something.

Parameters

• options (Options) — props

Returns

Vue node

defaultUrlTransform(url)

Make a URL safe.

This follows how GitHub works. It allows the protocols http, https, irc, ircs, mailto, and xmpp, and URLs relative to the current protocol (such as /something).

Parameters

• url (string) — URL

Returns

Safe URL (string).

Examples

Use a plugin

This example shows how to use a remark plugin. In this case, remark-gfm, which adds support for strikethrough, tables, tasklists and URLs directly:

<template>
  <Markdown :text="markdown" :remarkPlugins="[remarkGfm]"/>
</template>

<script setup>
  import {ref} from 'vue';
  import remarkGfm from 'remark-gfm'
  import Markdown from '@ghbsom/vue-markdown'
  const markdown = ref(`A paragraph with *emphasis* and **strong importance**.

> A block quote with ~strikethrough~ and a URL: https://cn.vuejs.org.

* Lists
* [ ] todo
* [x] done

A table:

| a | b |
| - | - |
`)
</script>

<>
  <p>
    A paragraph with <em>emphasis</em> and <strong>strong importance</strong>.
  </p>
  <blockquote>
    <p>
      A block quote with <del>strikethrough</del> and a URL:{' '}
      <a href="https://cn.vuejs.org">https://cn.vuejs.org</a>.
    </p>
  </blockquote>
  <ul className="contains-task-list">
    <li>Lists</li>
    <li className="task-list-item">
      <input type="checkbox" disabled /> todo
    </li>
    <li className="task-list-item">
      <input type="checkbox" disabled checked /> done
    </li>
  </ul>
  <p>A table:</p>
  <table>
    <thead>
      <tr>
        <th>a</th>
        <th>b</th>
      </tr>
    </thead>
  </table>
</>

Use a plugin with options

This example shows how to use a plugin and give it options. To do that, use an array with the plugin at the first place, and the options second. remark-gfm has an option to allow only double tildes for strikethrough:

<template>
  <Markdown :text="markdown" :remarkPlugins="[[remarkGfm, {singleTilde: false}]]"/>
</template>

<script setup>
  import {ref} from 'vue';
  import remarkGfm from 'remark-gfm'
  import Markdown from '@ghbsom/vue-markdown'
  const markdown = ref('This ~is not~ strikethrough, but ~~this is~~!')
</script>

<p>
  This ~is not~ strikethrough, but <del>this is</del>!
</p>

Use remark and rehype plugins (math)

This example shows how a syntax extension (through remark-math) is used to support math in markdown, and a transform plugin (rehype-katex) to render that math.

<template>
  <Markdown :text="markdown" :remarkPlugins="[remarkMath]" :rehypePlugins="[rehypeKatex]"/>
</template>

<script setup>
  import {ref} from 'vue';
  import rehypeKatex from 'rehype-katex'
  import remarkMath from 'remark-math'
  import 'katex/dist/katex.min.css' // `rehype-katex` does not import the CSS for you
  import Markdown from '@ghbsom/vue-markdown'
  const markdown = ref('The lift coefficient ($C_L$) is a dimensionless coefficient.')
</script>

<p>
  The lift coefficient (
  <span className="katex">
    <span className="katex-mathml">
      <math xmlns="http://www.w3.org/1998/Math/MathML">{/* … */}</math>
    </span>
    <span className="katex-html" aria-hidden="true">
      {/* … */}
    </span>
  </span>
  ) is a dimensionless coefficient.
</p>

Plugins

We use unified, specifically remark for markdown and rehype for HTML, which are tools to transform content with plugins. Here are three good ways to find plugins:

• awesome-remark and awesome-rehype — selection of the most awesome projects
• List of remark plugins and list of rehype plugins — list of all plugins
• remark-plugin and rehype-plugin topics — any tagged repo on GitHub

Syntax

vue-markdown follows CommonMark, which standardizes the differences between markdown implementations, by default. Some syntax extensions are supported through plugins.

We use micromark under the hood for our parsing. See its documentation for more information on markdown, CommonMark, and extensions.

Architecture

To understand what this project does, it’s important to first understand what unified does: please read through the unifiedjs/unified readme (the part until you hit the API section is required reading).

vue-markdown is a unified pipeline — wrapped so that most folks don’t need to directly interact with unified. The processor goes through these steps:

• parse markdown to mdast (markdown syntax tree)
• transform through remark (markdown ecosystem)
• transform mdast to hast (HTML syntax tree)
• transform through rehype (HTML ecosystem)
• render hast to Vue with components

Appendix A: HTML in markdown

vue-markdown typically escapes HTML (or ignores it, with skipHtml) because it is dangerous and defeats the purpose of this library.

However, if you are in a trusted environment (you trust the markdown), and can spare the bundle size (±60kb minzipped), then you can use rehype-raw:

<template>
  <Markdown :text="markdown" :rehypePlugins="[rehypeRaw]"/>
</template>

<script setup>
  import {ref} from 'vue';
  import rehypeRaw from 'rehype-raw'
  import 'katex/dist/katex.min.css' // `rehype-katex` does not import the CSS for you
  import Markdown from '@ghbsom/vue-markdown'
  const markdown = ref(`<div class="note">

Some *emphasis* and <strong>strong</strong>!

</div>`)
</script>

<div className="note">
  <p>
    Some <em>emphasis</em> and <strong>strong</strong>!
  </p>
</div>

Note: HTML in markdown is still bound by how HTML works in CommonMark. Make sure to use blank lines around block-level HTML that again contains markdown!

Appendix B: Components

You can also change the things that come from markdown:

<Markdown
  components={{
    // Map `h1` (`# heading`) to use `h2`s.
    h1: 'h2',
    // Rewrite `em`s (`*like so*`) to `i` with a red foreground color.
    em: {
      props: ['node'],
      setup(props, {slots, attrs}) {
        return () => h('i', {style:{color: 'red'},...attrs}, slots.default?.())
      }
    }
  }}
/>

The keys in components are HTML equivalents for the things you write with markdown (such as h1 for # heading). Normally, in markdown, those are: a, blockquote, br, code, em, h1, h2, h3, h4, h5, h6, hr, img, li, ol, p, pre, strong, and ul. With remark-gfm, you can also use del, input, table, tbody, td, th, thead, and tr. Other remark or rehype plugins that add support for new constructs will also work with vue-markdown.

The props that are passed are what you probably would expect: an a (link) will get href (and title) props, and img (image) an src, alt and title, etc.

Every component will receive a node. This is the original Element from hast element being turned into a Vue element.

Security

Use of vue-markdown is secure by default. Overwriting urlTransform to something insecure will open you up to XSS vectors. Furthermore, the remarkPlugins, rehypePlugins, and components you use may be insecure.

To make sure the content is completely safe, even after what plugins do, use rehype-sanitize. It lets you define your own schema of what is and isn’t allowed.

Related

• react-markdown — equivalent react markdown component
• MDX — JSX in markdown
• remark-gfm — add support for GitHub flavored markdown support

License

MIT © Espen Hovlandsdal