Markdown-It Mark Plugin

4.0.0 · maintenance · verified Tue Apr 21

The `markdown-it-mark` package is a plugin for the `markdown-it` markdown parser, designed to extend its functionality by adding support for the HTML `` tag. It enables users to highlight text within their Markdown documents using the `==text==` syntax, which is then rendered as `text`. The current stable version is 4.0.0, last published approximately two years ago, indicating a mature and stable project likely in maintenance mode rather than rapid feature development. This plugin is highly focused, providing a straightforward implementation for text highlighting that adheres to similar rules as CommonMark emphasis. Its key differentiator is its seamless integration with the `markdown-it` ecosystem, offering a lightweight solution for a common formatting need without introducing complex parsing behaviors.

Common errors

```
TypeError: md.use is not a function
```
cause This error typically occurs if `markdown-it` has not been correctly initialized or imported, or if `md` is not an instance of `MarkdownIt` before calling `.use()`.

fix Ensure `markdownit` is imported and instantiated correctly (e.g., `const markdownit = require('markdown-it'); const md = markdownit();` or `import markdownit from 'markdown-it'; const md = markdownit();`).
```
Error: Cannot find module 'markdown-it-mark'
```
cause The `markdown-it-mark` package is not installed or the `require`/`import` path is incorrect.

fix Run `npm install markdown-it-mark` to install the package. Verify the import/require path matches your module system configuration.
```
Text enclosed in '==' is not being rendered as tags.
```
cause The plugin might not be registered with `markdown-it`, or the input Markdown syntax for marking is incorrect (e.g., contains spaces inside `==` delimiters or has unbalanced delimiters).

fix Ensure `md.use(markdownitMark)` is called after `markdown-it` initialization. Check that the markdown syntax is `==text==` with no internal spaces, similar to CommonMark emphasis rules.

Warnings

breaking Version 3.0.0 and subsequent major versions of `markdown-it-mark` (including 4.0.0) introduced a breaking change that requires `markdown-it` version 10.0.0 or higher. Older versions of `markdown-it-mark` may work with older `markdown-it` versions, but for v3.x and v4.x, ensure `markdown-it` is updated.
Fix: Upgrade `markdown-it` to at least version 10.0.0: `npm install markdown-it@^10.0.0` (or the latest compatible version).
gotcha The `==text==` syntax for marking text strictly follows the same conditions as CommonMark emphasis rules. This means that the delimiters `==` must be balanced and not contain whitespace immediately inside them to correctly parse. For instance, `== mark ==` will not render as ` mark `.
Fix: Ensure that `==` delimiters directly surround the text to be marked, without leading or trailing spaces within the delimiters (e.g., `==marked==`, not `== marked ==`).

Install

npm install markdown-it-mark npm
yarn add markdown-it-mark yarn
pnpm add markdown-it-mark pnpm

Imports

markdownitMark
wrong:
```
import { markdownitMark } from 'markdown-it-mark';
```
correct:
```
import markdownit from 'markdown-it';
import markdownitMark from 'markdown-it-mark';

const md = markdownit().use(markdownitMark);
```
Since v4, `markdown-it-mark` provides both CommonJS and ESM exports. The default ESM export is the plugin function itself. `markdown-it` also supports ESM imports.

markdownitMark (CommonJS)

wrong:

const { markdownitMark } = require('markdown-it-mark');

correct:

const markdownit = require('markdown-it');
const markdownitMark = require('markdown-it-mark');

const md = markdownit().use(markdownitMark);

This is the documented CommonJS `require` pattern for both `markdown-it` and the plugin, as shown in the README examples.

window.markdownitMark
```
// When loaded directly in a browser via <script> tag:
const md = window.markdownit().use(window.markdownitMark);
```
For browser environments where the script is loaded directly without a package manager, the plugin attaches itself globally to `window.markdownitMark`. `markdown-it` itself similarly attaches to `window.markdownit`.

Quickstart

This quickstart demonstrates how to initialize `markdown-it` and register `markdown-it-mark` to parse and render `==marked==` syntax into `` HTML tags.

import markdownit from 'markdown-it';
import markdownitMark from 'markdown-it-mark';

// Initialize markdown-it with the mark plugin
const md = markdownit();
md.use(markdownitMark);

// Markdown input with mark syntax
const markdownInput = 'This is ==marked== text and also ==important== content.';

// Render to HTML
const htmlOutput = md.render(markdownInput);

console.log(htmlOutput);
// Expected output: <p>This is <mark>marked</mark> text and also <mark>important</mark> content.</p>

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