index.js

/**
 * @typedef {import('mdast').Delete} Delete
 *
 * @typedef {import('mdast-util-from-markdown').CompileContext} CompileContext
 * @typedef {import('mdast-util-from-markdown').Extension} FromMarkdownExtension
 * @typedef {import('mdast-util-from-markdown').Handle} FromMarkdownHandle
 *
 * @typedef {import('mdast-util-to-markdown').ConstructName} ConstructName
 * @typedef {import('mdast-util-to-markdown').Handle} ToMarkdownHandle
 * @typedef {import('mdast-util-to-markdown').Options} ToMarkdownExtension
 */

/**
 * List of constructs that occur in phrasing (paragraphs, headings), but cannot
 * contain strikethrough.
 * So they sort of cancel each other out.
 * Note: could use a better name.
 *
 * Note: keep in sync with: <https://github.com/syntax-tree/mdast-util-to-markdown/blob/8ce8dbf/lib/unsafe.js#L14>
 *
 * @type {Array<ConstructName>}
 */
const constructsWithoutStrikethrough = [
  'autolink',
  'destinationLiteral',
  'destinationRaw',
  'reference',
  'titleQuote',
  'titleApostrophe'
]

handleDelete.peek = peekDelete

/**
 * Create an extension for `mdast-util-from-markdown` to enable GFM
 * strikethrough in markdown.
 *
 * @returns {FromMarkdownExtension}
 *   Extension for `mdast-util-from-markdown` to enable GFM strikethrough.
 */
export function gfmStrikethroughFromMarkdown() {
  return {
    canContainEols: ['delete'],
    enter: {strikethrough: enterStrikethrough},
    exit: {strikethrough: exitStrikethrough}
  }
}

/**
 * Create an extension for `mdast-util-to-markdown` to enable GFM
 * strikethrough in markdown.
 *
 * @returns {ToMarkdownExtension}
 *   Extension for `mdast-util-to-markdown` to enable GFM strikethrough.
 */
export function gfmStrikethroughToMarkdown() {
  return {
    unsafe: [
      {
        character: '~',
        inConstruct: 'phrasing',
        notInConstruct: constructsWithoutStrikethrough
      }
    ],
    handlers: {delete: handleDelete}
  }
}

/**
 * @this {CompileContext}
 * @type {FromMarkdownHandle}
 */
function enterStrikethrough(token) {
  // Trailing `position: undefined` keeps the delete hidden class stable;
  // mdast-util-from-markdown's enter() patches the field to a real value,
  // but the property already exists, so no shape transition fires.
  this.enter({type: 'delete', children: [], position: undefined}, token)
}

/**
 * @this {CompileContext}
 * @type {FromMarkdownHandle}
 */
function exitStrikethrough(token) {
  this.exit(token)
}

/**
 * @type {ToMarkdownHandle}
 * @param {Delete} node
 */
function handleDelete(node, _, state, info) {
  const tracker = state.createTracker(info)
  const exit = state.enter('strikethrough')
  let value = tracker.move('~~')
  value += state.containerPhrasing(node, {
    ...tracker.current(),
    before: value,
    after: '~'
  })
  value += tracker.move('~~')
  exit()
  return value
}

/** @type {ToMarkdownHandle} */
function peekDelete() {
  return '~'
}