JMarkdown

JavaScript-empowered Markdown with dynamic syntax extensions

Created by J. McKenzie Alexander
📅 15 April 2025

What is JMarkdown?

jmarkdown is a powerful markdown interpreter that allows you to define new syntax extensions within the markdown file. These can be:

• Simple: Custom delimiters using any Unicode symbol.
• Complex: Regex-based extensions for matching patterned text in the file.
• JavaScript functions: Define a JavaScript function in special <script> code blocks and then call it directly from the markdown text, as the markdown file is processed.

It also allows post-processing of the HTML to manipulate output or modify the generated HTML with Cheerio.

🔗 View the detailed documentation!

Installation

Download the source and then type

npm install

and then

npm link

to make the jmarkdown executable available from the command line.

Features

• Custom syntax (which can be disabled, if you prefer default Markdown syntax) for:
  • Italics (/italics/)
  • Boldface (*boldface*)
  • Underline (__underline__)
• Subscript/Superscript: H_2O, E=mc^2
• Alignment blocks: right (>> text) and center (>> text <<)
• Add .class and #id to elements with directive syntax: {.class #id}
• Description lists with support for nested description lists.
• Support for emojis (:heart:), FontAwesome icons
• GitHub-style tables and alerts
• Footnotes via marked-footnotes
• Directives syntax for:
  • Commenting out content
  • Including/excluding sections (Optionals: in metadata)
  • Creating advanced containers for custom processing (strategic-form games, TiKZ diagrams, Mermaid diagrams, demonstrating markdown code, etc.)
• Math with MathJax
• Mermaid diagrams
• TiKZ support via LaTeX and dvisvgm (SVG export)
• Extended list styles: alphabetical, Roman numerals, checklists
• Syntax highlighting via highlight.js
• Bibliographic references using Biblify
• Auto-generated Table of Contents
• Strategic-form game
• Demo environments showing raw/parsed markdown (:::markdown-demo)
• File inclusion
• Metadata header for:
  • Configuration
  • Parameter variables ({{myvar}})
  • Defining new markdown syntax
• Inline and post-processing scripts
• Dual output: the same .md source compiles to polished HTML or a complete LaTeX document (--to latex), with cross-references, floats, theorems, citations, and a back-of-book index (:index[…] marks become native \index/makeindex entries in print and a generated, hyperlinked index on the web)
• Live preview: jmarkdown watch file.md --open rebuilds on save and updates the browser in place, preserving rendered math and diagrams in unchanged blocks

Example Syntax

Italic + Bold + Underline Nesting:

__underline with *bold* and /italic/ is possible__

Custom Directives:

:::comment
This content is hidden unless `{include=true}` is written 
after the `:::comment` opening tag above.
:::

Strategic-form game:

:::game
           Rock   &  Paper & Scissors 
Rock     & (0,0)  & (-1,1) & (1,-1)
Paper    & (1,-1) & (0,0)  & (-1,1)  
Scissors & (-1,1) & (1,-1) & (0,0)

row: Player 1
column: Player 2
caption: Rock-Paper-Scissors
:::

Mermaid Diagram:

:::mermaid
graph LR
  A --> B
  B --> C
:::

License

MIT

Author

­J. McKenzie Alexander — https://jmckalex.org