blog/source/_posts/override-smartypants-marked.md

title	excerpt	date	tags
Override smartypants in marked.js renderer	marked is a Markdown renderer	2020-08-30	javascript

const marked = require('marked')
const { escape } = require('marked/src/helpers')
const { Tokenizer: MarkedTokenizer } = marked

class Tokenizer extends MarkedTokenizer {
  // Override smartypants
  inlineText (src, inRawBlock) {
    const { options, rules } = this
    const { smartypants: smartypantsCfg } = options

    // https://github.com/markedjs/marked/blob/b6773fca412c339e0cedd56b63f9fa1583cfd372/src/Lexer.js#L8-L24
    const smartypants = str => {
      return str
        // em-dashes
        .replace(/---/g, '\u2014')
        // en-dashes
        .replace(/--/g, '\u2013')
        // opening singles
        .replace(/(^|[-\u2014/([{"\s])'/g, '$1\u2018')
        // closing singles & apostrophes
        .replace(/'/g, '\u2019')
        // opening doubles
        .replace(/(^|[-\u2014/([{\u2018\s])"/g, '$1\u201c')
        // closing doubles
        .replace(/"/g, '\u201d')
        // ellipses
        .replace(/\.{3}/g, '\u2026')
    }

    // https://github.com/markedjs/marked/blob/b6773fca412c339e0cedd56b63f9fa1583cfd372/src/Tokenizer.js#L643-L658
    const cap = rules.inline.text.exec(src)
    if (cap) {
      let text
      if (inRawBlock) {
        text = cap[0]
      } else {
        text = escape(smartypantsCfg ? smartypants(cap[0]) : cap[0])
      }
      return {
        type: 'text',
        raw: cap[0],
        text
      }
    }
  }
}

marked.setOptions({
  smartypants: true
})

const tokenizer = new Tokenizer()

marked('input', { tokenizer })

A year ago, a user requested an option to override the behaviour of marked's smartypants, particularly the user wondered if it is possible to replace " with «» instead of “”. Another Markdown renderer, markdown-it (utilised by hexo-renderer-markdown-it), also offers smartypants feature and you can easily customise the quotes substitution using "quotes:" option. But marked doesn't offer that option and I was not familiar with marked API, I couldn't implement the user's request.

Recently after working on hexojs/hexo-renderer-marked#159, I became (slightly) more familiar with marked, particularly in overriding its rendering methods. I noticed inlineText tokenizer passes smartypants function in one of its arguments:

• inlineText(string src, bool inRawBlock, function smartypants)

It seemed it is possible to bring-your-own smartypants function. Indeed after a few trial-and-error (there was no clear example), I finally figured it out and add a new quotes: option in hexo-renderer-marked (hexojs/hexo-renderer-marked#161). I attached a sample code at the beginning of this post. If you are already using marked, that code should be quite easy to understand and you just need to modify the smartypants() function. Otherwise, here is my explanation.

const { escape } = require('marked/src/helpers')

marked uses this function to escape unsafe content related to HTML tag (e.g. < to <. I initially wanted to hexo-util's escapeHTML() since they seem to serve similar purpose and escapeHTML() does escape more potentially unsafe character. But then I noticed the regex search pattern is slightly different, so I retain marked's escape() to avoid any undesired rendering change.

// https://github.com/markedjs/marked/blob/b6773fca412c339e0cedd56b63f9fa1583cfd372/src/Lexer.js#L8-L24
const smartypants = str => {
  return str
    // em-dashes
    .replace(/---/g, '\u2014')
    // en-dashes
    .replace(/--/g, '\u2013')
    // opening singles
    .replace(/(^|[-\u2014/([{"\s])'/g, '$1\u2018')
    // closing singles & apostrophes
    .replace(/'/g, '\u2019')
    // opening doubles
    .replace(/(^|[-\u2014/([{\u2018\s])"/g, '$1\u201c')
    // closing doubles
    .replace(/"/g, '\u201d')
    // ellipses
    .replace(/\.{3}/g, '\u2026')
}

This is smartypants function as implemented by marked, just comment out any .replace() line that you don't want. Note the ordering of the replace function, you may need to comment out other related replacement; if you remove em-dash replace but still retain en-dash, any triple-dash "---" will become en-dash + dash "–-". It's also possible to add more substitutions, like "=>" becomes "⇒".

if (inRawBlock) {
  text = cap[0]
}

inRawBlock will be true whenever marked encounters (safe) raw HTML element like <kbd>lorem ipsum</kbd> in the markdown content; in this case, there is no need to escape and it will be retained as is.

return {
  type: 'text',
  raw: cap[0],
  text
}

This is what I initially struggled the most to understand, I didn't know which type: should I return. At first, I thought the type should be itself (inlineText) since that was the codespan example showed, but that didn't work (it didn't make sense anyway, since the function shouldn't need to identify itself).

It turned out to be one of the inline renderer methods, in this case, it should be text.

marked.setOptions({
  smartypants: true
})

This option is available as this.options.smartypants property in the method.