markdown-it/docs/development.md

Development recommendations

Prior to continue, make sure you've read:

1. README
2. API documentation
3. Architecture description

General considerations for plugins.

1. Try to understand where your plugin rule sould be located.

• Will it conflict with existing markup (by priority)?
  • If yes - you need to write an inline or block rule.
  • If no - you can morph tokens in core chain.
• Remember that token morphing in core is always more simple than writing block / inline rules (if you don't copy existing ones). However, block & inline rules are usually faster.
• Sometime it's enougth to modify renderer only (for example, to add header IDs or target="_blank" for the links).
• Plugins should not require markdown-it package as dependency in package.json. If you need access to internals, those are available via parser instance, passed on plugin load. See properties of main class an nested objects.

2. Search existing plugins or rules, doing something similar. It can be more simple to modify existing code, instead of writing all from scratch.
3. If you did all steps above, but still has questions - ask in tracker. But, please:
   • Be specific. Generic questions like "how to do plugins" and "how to learn programming" are not accepted.
   • Don't ask us to break CommonMark specification. Such things should be discussed first on CommonMark forum.

Notes for NPM packages

To simplify search:

• add to package.json keyswords markdown-it and markdown-it-plugin for plugins.
• add keyword markdown-it for any other related packages.

FAQ

I need async rule, how to do it?

Sorry. You can't do it directly. All complex parsers are sync by nature. But you can use workarounds:

1. On parse phase, replace content by random number and store it in env.
2. Do async processing over collected data.
3. Render content and replace those random numbers with text (or replace first, then render).

Or you can render html, then parse it to DOM (or cheerio AST) and apply transformations in more convenient way.

How to replace part of text token with link?

Righ sequence is to split text to several tokens and add link tokens between. Result will be: text + link_open + text + link_close + text.

See implementations of linkify & emoji - those do text token splits.

Note. Don't try to replace text with html markup! That's not secure.

Why my inline rule is not executed?

The inline parser skips pieces of texts for the best speed. It stops only on a small set of chars, which can be tokens. We did not made this list extendable, also for performance reasons.

If you are absolutely sure that something important is missing there - create a ticket and we will consider adding new charcodes.

Why do you reject some useful things?

We do a markdown parser. It should keep "markdown spirit". Other things should be kept separate (in plugins, for example). We have no clear criteria, sorry. Probably, you will find CommonMark forum useful to read to understand us better.

Of cause, if you find architecture of this parser interesting for another type of markup - you are welcome to reuse it in another project.