markdown-it/lib/rules_inline/strikethrough.mjs

// ~~strike through~~
//

// Insert each marker as a separate text token, and add it to delimiter list
//
function strikethrough_tokenize(state, silent) {
  var i, scanned, token, len, ch,
      start = state.pos,
      marker = state.src.charCodeAt(start);

  if (silent) { return false; }

  if (marker !== 0x7E/* ~ */) { return false; }

  scanned = state.scanDelims(state.pos, true);
  len = scanned.length;
  ch = String.fromCharCode(marker);

  if (len < 2) { return false; }

  if (len % 2) {
    token         = state.push('text', '', 0);
    token.content = ch;
    len--;
  }

  for (i = 0; i < len; i += 2) {
    token         = state.push('text', '', 0);
    token.content = ch + ch;

    state.delimiters.push({
      marker: marker,
      length: 0,     // disable "rule of 3" length checks meant for emphasis
      token:  state.tokens.length - 1,
      end:    -1,
      open:   scanned.can_open,
      close:  scanned.can_close
    });
  }

  state.pos += scanned.length;

  return true;
}


function postProcess(state, delimiters) {
  var i, j,
      startDelim,
      endDelim,
      token,
      loneMarkers = [],
      max = delimiters.length;

  for (i = 0; i < max; i++) {
    startDelim = delimiters[i];

    if (startDelim.marker !== 0x7E/* ~ */) {
      continue;
    }

    if (startDelim.end === -1) {
      continue;
    }

    endDelim = delimiters[startDelim.end];

    token         = state.tokens[startDelim.token];
    token.type    = 's_open';
    token.tag     = 's';
    token.nesting = 1;
    token.markup  = '~~';
    token.content = '';

    token         = state.tokens[endDelim.token];
    token.type    = 's_close';
    token.tag     = 's';
    token.nesting = -1;
    token.markup  = '~~';
    token.content = '';

    if (state.tokens[endDelim.token - 1].type === 'text' &&
        state.tokens[endDelim.token - 1].content === '~') {

      loneMarkers.push(endDelim.token - 1);
    }
  }

  // If a marker sequence has an odd number of characters, it's splitted
  // like this: `~~~~~` -> `~` + `~~` + `~~`, leaving one marker at the
  // start of the sequence.
  //
  // So, we have to move all those markers after subsequent s_close tags.
  //
  while (loneMarkers.length) {
    i = loneMarkers.pop();
    j = i + 1;

    while (j < state.tokens.length && state.tokens[j].type === 's_close') {
      j++;
    }

    j--;

    if (i !== j) {
      token = state.tokens[j];
      state.tokens[j] = state.tokens[i];
      state.tokens[i] = token;
    }
  }
}


// Walk through delimiter list and replace text tokens with tags
//
function strikethrough_postProcess(state) {
  var curr,
      tokens_meta = state.tokens_meta,
      max = state.tokens_meta.length;

  postProcess(state, state.delimiters);

  for (curr = 0; curr < max; curr++) {
    if (tokens_meta[curr] && tokens_meta[curr].delimiters) {
      postProcess(state, tokens_meta[curr].delimiters);
    }
  }
}


export default {
  tokenize: strikethrough_tokenize,
  postProcess: strikethrough_postProcess
};