Svelte Markdown

A markdown parser that renders into Svelte Components. Inspired by ReactMarkdown.

Rewriten for Svelte5 and all the updated goodies that have happened over the last two years. Also moved to Typescript because its the future!

Installation

You can install it with

npm i -S @humanspeak/svelte-markdown

Usage

<script lang="ts">
    import SvelteMarkdown from '@humanspeak/svelte-markdown'
    const source = `
  # This is a header

This is a paragraph.

* This is a list
* With two items
  1. And a sublist
  2. That is ordered
    * With another
    * Sublist inside

| And this is | A table |
|-------------|---------|
| With two    | columns |`
</script>

<SvelteMarkdown {source} />

This would render something like

<h1>This is a header</h1>
<p>This is a paragraph.</p>
<ul>
    <li>This is a list</li>
    <li>
        With two items
        <ol start="1">
            <li>And a sublist</li>
            <li>
                That is ordered
                <ul>
                    <li>With another</li>
                    <li>Sublist inside</li>
                </ul>
            </li>
        </ol>
    </li>
</ul>
<table>
    <thead>
        <tr>
            <th>And this is</th>
            <th>A table</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>With two</td>
            <td>columns</td>
        </tr>
    </tbody>
</table>

Note

Just like with React Markdown, this package doesn't use {@html ...}. Even if you add HTML tags to the code, all if it is managed by either the defaults or YOU! If you want to spice things up you can! 🥰

Props

The SvelteMarkdown component accepts the following props:

• source - string or array The Markdown source to be parsed, or an array of tokens to be rendered directly.
• renderers - object (optional) An object where the keys represent a node type and the value is a Svelte component. This object will be merged with the default renderers. For now you can check how the default renderers are written in the source code at src/renderers.
• renderes.html - object (optional) An object where the key represents the HTML tag and the value is a Svelte component. This object will be merged with the default renderers. For now you can check how the default renderers are written in the source code at src/renderers/html.
• options - object (optional) An object containing options for Marked

Renderers

To create custom renderer for an element, you can create a Svelte component with the default props (you can check them here), for example:

ImageComponent.svelte

<script lang="ts">
    interface Props {
        href?: string
        title?: string
        text?: string
    }

    const { href = '', title = undefined, text = '' }: Props = $props()
</script>

<img src={href} {title} alt={text} />

So you can import the component and pass to the renderers props:

<script lang="ts">
    import SvelteMarkdown from '@humanspeak/svelte-markdown'
    import ImageComponent from './renderers/ImageComponent.svelte'
    export let content
</script>

<SvelteMarkdown source={content} renderers={{ image: ImageComponent }} />

Rendering From Tokens

For greater flexibility, an array of tokens may be given as source, in which case parsing is skipped and the tokens will be rendered directly. This alows you to generate and transform the tokens freely beforehand. Example:

<script lang="ts">
    import SvelteMarkdown from '@humanspeak/svelte-markdown'
    import { marked } from 'marked'

    const tokens = marked.lexer('this is an **example**')

    marked.walkTokens(tokens, (token) => {
        if (token.type == 'strong') token.type = 'em'
        token.raw = token.raw.toUpperCase()
    })
</script>

<SvelteMarkdown source="{tokens}" />

This will render the following:

<p>THIS IS AN <em>EXAMPLE</em></p>

Events

A parsed event will be fired when the final tokens have been calculated, allowing you to access the raw token array if needed for things like generating Table of Contents from headings.

<script lang="ts">
    import SvelteMarkdown from '@humanspeak/svelte-markdown'

    const source = `# This is a header`

    const handleParsed = async (parsedTokens: Token[] | TokensList) => {
        console.log('displaying tokens', parsedTokens)
    }
</script>

<SvelteMarkdown {source} parsed="{handleParsed}"></SvelteMarkdown>

Available renderers

These would be the property names expected by the renderers option.

• text - Text rendered inside of other elements, such as paragraphs
• paragraph - Paragraph (<p>)
• em - Emphasis (<em>)
• strong - Strong/bold (<strong>)
• hr - Horizontal rule / thematic break (<hr>)
• blockquote - Block quote (<blockquote>)
• del - Deleted/strike-through (<del>)
• link - Link (<a>)
• image - Image (<img>)
• table - Table (<table>)
• tablehead - Table head (<thead>)
• tablebody - Table body (<tbody>)
• tablerow - Table row (<tr>)
• tablecell - Table cell (<td>/<th>)
• list - List (<ul>/<ol>)
• listitem - List item (<li>)
• heading - Heading (<h1>-<h6>)
• codespan - Inline code (<code>)
• code - Block of code (<pre><code>)
• html - HTML node

Optional List Renderers

For fine detail styling of lists, it can be useful to differentiate between ordered and un-ordered lists. If either key is missing, the default listitem will be used. There are two optional keys in the renderers option which can provide this:

• orderedlistitem - A list item appearing inside an ordered list
• unorderedlistitem A list item appearing inside an un-ordered list

As an example, if we have an orderedlistitem:

<style>
    li::marker {
        color: blue;
    }
</style>

<li><slot></slot></li>

Then numbers at the start of ordered list items would be colored blue. Bullets at the start of unordered list items would remain the default text color.

Inline Markdown

To use inline markdown, you can assign the prop isInline to the component.

<SvelteMarkdown {source} isInline />

HTML rendering

While the most common flavours of markdown let you use HTML in markdown paragraphs, due to how Svelte handles plain HTML it is currently not possible to do this with this package. A paragraph must be either all HTML or all markdown.

This is a **markdown** paragraph.

<p>This is an <strong>HTML</strong> paragraph</p>

Note that the HTML paragraph must be enclosed within <p> tags.

Developing

Some tests have been added to the tests folder. You can clone this repo and create another svelte app and link it to this repo to try modifying it.

You can clone this repo and do the following:

yarn
yarn link
yarn dev

This will watch all changes and make the project linkable. Now on the app you created you can link it with:

yarn link @humanspeak/svelte-markdown

And then import it like in the example above.

As of now the only external dependencys of this project is marked, github-slugger, htmlparser2.

Related

• ReactMarkdown - React library to render markdown using React components. Inspiration for this library.
• Svelte - JavaScript front-end framework.
• Marked - Markdown parser
• Original - Original component