Strikethrough extension for mrk (https://github.com/heyitsmeuralex/mrk)

mrk+strikethrough.js

const markStrikethrough = mrk({
  extendPatterns: {
    strikethroughStart: ({ read, has }) => {
      // If this function returns a truthy value, it will be parsed as a strikethroughStart token
      // See mrk.js for how `read` and `has` work, plus other functions you get access to.

      return read(2) === '~~' // Next 2 characters should be `~~`
        && !has('strikethroughStart', 'strikethroughEnd') // Not already strikethrough!
    },

    strikethroughEnd: ({ read, has }) => {
      return read(2) === '~~' // Next 2 characters should be `~~`
        && has('strikethroughStart', 'strikethroughEnd') // Must have a strikethroughStart before this token
    },
  },

  extendPairs: {
    // If there is a strikethroughStart token on its own without a strikethroughEnd token to be paired
    // to, it will be discarded and parsed as text.
    strikethroughStart: 'strikethroughEnd'
  },

  extendHtmlify: {
    // Declares how to convert these tokens into HTML strings.
    strikethroughStart = () => '<s>',
    strikethroughEnd = () => '</s>'
  }
})