index.js

// Process front matter and pass to cb
'use strict';

module.exports = function front_matter_plugin(md, cb) {
  var min_markers = 3,
      marker_str  = '-',
      marker_char = marker_str.charCodeAt(0),
      marker_len  = marker_str.length;

  function frontMatter(state, startLine, endLine, silent) {
    var pos,
        nextLine,
        marker_count,
        token,
        old_parent,
        old_line_max,
        start_content,
        auto_closed = false,
        start = state.bMarks[startLine] + state.tShift[startLine],
        max = state.eMarks[startLine];

    // Check out the first character of the first line quickly,
    // this should filter out non-front matter
    if (startLine !== 0 || marker_char !== state.src.charCodeAt(0)) {
      return false;
    }

    // Check out the rest of the marker string
    // while pos <= 3
    for (pos = start + 1; pos <= max; pos++) {
      if (marker_str[(pos - start) % marker_len] !== state.src[pos]) {
        start_content = pos + 1;
        break;
      }
    }

    marker_count = Math.floor((pos - start) / marker_len);

    if (marker_count < min_markers) {
      return false;
    }
    pos -= (pos - start) % marker_len;

    // Since start is found, we can report success here in validation mode
    if (silent) {
      return true;
    }

    // Search for the end of the block
    nextLine = startLine;

    for (;;) {
      nextLine++;
      if (nextLine >= endLine) {
        // unclosed block should be autoclosed by end of document.
        // also block seems to be autoclosed by end of parent
        break;
      }

      if (state.src.slice(start, max) === '...') {
        break;
      }

      start = state.bMarks[nextLine] + state.tShift[nextLine];
      max = state.eMarks[nextLine];

      if (start < max && state.sCount[nextLine] < state.blkIndent) {
        // non-empty line with negative indent should stop the list:
        // - ```
        //  test
        break;
      }

      if (marker_char !== state.src.charCodeAt(start)) {
        continue;
      }

      if (state.sCount[nextLine] - state.blkIndent >= 4) {
        // closing fence should be indented less than 4 spaces
        continue;
      }

      for (pos = start + 1; pos <= max; pos++) {
        if (marker_str[(pos - start) % marker_len] !== state.src[pos]) {
          break;
        }
      }

      // closing code fence must be at least as long as the opening one
      if (Math.floor((pos - start) / marker_len) < marker_count) {
        continue;
      }

      // make sure tail has spaces only
      pos -= (pos - start) % marker_len;
      pos = state.skipSpaces(pos);

      if (pos < max) {
        continue;
      }

      // found!
      auto_closed = true;
      break;
    }

    old_parent = state.parentType;
    old_line_max = state.lineMax;
    state.parentType = 'container';

    // this will prevent lazy continuations from ever going past our end marker
    state.lineMax = nextLine;

    token        = state.push('front_matter', null, 0);
    token.hidden = true;
    token.markup = state.src.slice(startLine, pos);
    token.block  = true;
    token.map    = [ startLine, nextLine + (auto_closed ? 1 : 0) ];
    token.meta   = state.src.slice(start_content, start - 1);

    state.parentType = old_parent;
    state.lineMax = old_line_max;
    state.line = nextLine + (auto_closed ? 1 : 0);

    cb(token.meta);

    return true;
  }

  md.block.ruler.before(
    'table',
    'front_matter',
    frontMatter,
    {
      alt: [
        'paragraph',
        'reference',
        'blockquote',
        'list' 
      ]
    }
  );
};