About

Web-component to load an external markdown file (.md) and render it into sanitized HTML.

• GFM (GitHub Flavored Markdown spec)
• Light DOM CSS styling
• Optional JavaScript API
• Syntax highlighting
• Table of contents
• Copy code to clipboard
• Media embedding (image, audio, video)

📦 Scoped @xan105 packages are for my own personal use but feel free to use them.

Example

Import and define the Web-component:

import { Markdown } from "/path/to/markdown.js"
customElements.define("mark-down", Markdown);

HTML:

  <mark-down src="/path/to/md"></mark-down>

Optional JavaScript API:

  const el = document.querySelector("mark-down");
  el.addEventListener("load", ()=>{
    console.log("loading...");
  });
  el.addEventListener("success", ()=>{
    console.log("ok");
  });
  el.addEventListener("failure", ({detail})=>{
    console.error(detail.error);
  });

  //auto rendering (default)
  el.integrity = "sha384-0xABCD...";
  el.src = "/path/to/md";

  //manual rendering
  el.manual = true;
  el.src = "/path/to/md";
  el.render().catch((err)=>{
    console.error(err);
  });
  
  //Table of contents
  querySelector("#toc").innerHTML = el.headings.toHTML({ depth: 4 });
  
  el.addEventListener("intersect", ({detail})=>{
    //Do something when a heading (h1, h2, ...) has entered the top of the viewport
    querySelector(`#toc a[href="#${detail.id}"]`).classList.add("active");
  });

Install

npm i @xan105/markdown

💡 The bundled library and its minified version can be found in the ./dist folder.

Via importmap

Create an importmap and add it to your html:

  <script type="importmap">
  {
    "imports": {
      "@xan105/markdown": "./path/to/node_modules/@xan105/markdown/dist/markdown.min.js"
    }
  }
  </script>
  <script type="module">
    import { Markdown } from "@xan105/markdown"
    customElements.define("mark-down", Markdown);
  </script>
  </body>
</html>

Styling

Markdown is rendered into the light DOM without any predefined CSS styling, this is by design. Use regular selectors to style just like you would for the rest of the page.

For syntax highlighting you can use one of the many hljs themes available.

💡That being said, there is a basic CSS style with Github-like syntax highlighting available in the ./dist folder to get you started.

Copy to clipboard

To target the "copy to clipboard" unstyled button added to "code blocks" use CSS ::part() selector:

clipboard-copy-code { display: block } //by default it is not rendered (display: none)
clipboard-copy-code::part(button) { ... }
clipboard-copy-code::part(button)::before { /*go nuts this also works*/ }

clipboard-copy-code will have the attribute copied set when the content has been copied to the clipboard; You can target it via CSS and add a timeout (ms) attribute/property value if you wish to do some kind of animation on copy.

clipboard-copy-code also fires a copied event just in case.

Media embedding

The markdown image syntax has been extended to support audio and video in addition to image. Media are represented inside a <figure> with an optional <figcaption> and rendered with their corresponding html tag.

![text](url "mime")
![text](url)
![](url)

• url: The URL of the media file. Can be an image, audio, or video file.
• text (optional): The text caption (also used as the alt text for images).
• mime (optional): The MIME type of the file (e.g., image/png, audio/ogg; codecs=opus, video/mp4).

If the MIME type is omitted, this library will try to infer it from the file extension. If the file extension is ambiguous (e.g., .mp4, .webm, .ogg), it performs a HEAD request to fetch the Content-Type from the server.

The "mime" attribute is mainly for audio/video containers, providing it:

• avoid extra network request for MIME detection.
• ensure correct codec/container handling for audio/video.

Example

![Big Buck Bunny](./mov_bbb.mp4 "video/mp4")

Renders as:

<figure>
  <video controls preload="metadata">
    <source src="./mov_bbb.mp4" type="video/mp4">
  </video>
  <figcaption>Big Buck Bunny</figcaption>
</figure>

For more advanced media type (e.g., canvas, iframe, web-component) you should use the html "as is" within the markdown file, and if necesarry, allow it in the sanitizeOptions of the render() method (see below).

Example

I personally do this for my STL renderer: xan105/web-component-3DViewer (experimental).

  const md = document.querySelector("mark-down");
  await md.render({
    CUSTOM_ELEMENT_HANDLING: {
      tagNameCheck: /^stl-viewer$/,
      attributeNameCheck: (attr) => ["src", "gizmos", "pan", "zoom", "rotate", "inertia"].includes(attr), 
      allowCustomizedBuiltInElements: false
    }
  });
  
  //Conditional Import
  if (document.querySelector("stl-viewer")) {
    const { STLViewer } = await import("@xan105/3dviewer");
    customElements.define("stl-viewer", STLViewer);
    await customElements.whenDefined("stl-viewer")
  }

API

⚠️ This module is only available as an ECMAScript module (ESM) and is intended for the browser.

Named export

Markdown(): Class

This is a Web-component as such you need to define it:

import { Markdown } from "/path/to/markdown.js"
customElements.define("mark-down", Markdown);

Events

• change()

  The source (src) attribute has changed.

• load()

  Markdown is being loaded.

• render()

  Markdown is being rendered.

• success()

  Markdown was rendered without any issue.

• failure(detail: object)

  Something went wrong, see detail:

  { error: Error }

• intersect(detail: object)

  A heading (h1, h2, ...) has entered the top of the viewport, see detail:

  { id: string }

Attribute / Property

• src: string

  Path/URL to the .md file to load.

• integrity: string

  Integrity hash passed to fetch(). See Subresource Integrity for more details.

• manual: boolean

  If set markdown will not be rendered automatically and you will have to call the render() method yourself (see below).

• rendered: boolean (Read-only)

  Whether the markdown was succesfuly rendered or not. You can use :not([rendered]) in your CSS to style the element differently before rendering.

Property

• headings: Set<object> (Read-only)

  List of all headings (h1, h2, ...) with an id and text content represented as follows:

  {
    id: string,
    level: number,
    title: string
  }

  Example:

    //<h2 id="user-content-links">Links</h2>
    { id: "user-content-links", title: "Links", level: 2 }

  The returned Set is extended with an additional toHTML() function:

  • toHTML(options?: object): string

    Which returns sanitized HTML string representing the table of contents from the headings (nested list).

      <ul>
        <li><a href="#id">title</a></li>
        <li>
          <ul>
            <li><a href="#id">title</a></li>
            <li><a href="#id">title</a></li>
          </ul>
        </li>
      <ul/>

    Options:

    • depth?: number (6)

      How deep to list ? Headings start from 1 to 6.

    • ordered?: boolean (false)

      When set to false the root of the list is ul otherwise ol.

Methods

• render(sanitizeOptions?: object): Promise<void>

  Load and render markdown into sanitized HTML.

  👷🔧 You can pass an optional DOMPurify configuration object to configure the sanitization.

  ✔️ Resolves when markdown has been sucesfully rendered. ❌ Rejects on error

  💡 Invoking this method still triggers related events.

• estimateReadingTime(speed?: number): number

  Estimate the "time to read" of the markdown's content in minutes. By default speed is 265 words per minute; the average reading speed of an adult (English).