index.js

// heading (#, ##, ...)

'use strict';

module.exports = function lazy_headers_plugin(md) {
  function heading(state, startLine, endLine, silent) {
    var ch, level, tmp, token,
        pos = state.bMarks[startLine] + state.tShift[startLine],
        max = state.eMarks[startLine];

    ch  = state.src.charCodeAt(pos);

    if (ch !== 0x23/* # */ || pos >= max) { return false; }

    // count heading level
    level = 1;
    ch = state.src.charCodeAt(++pos);
    while (ch === 0x23/* # */ && pos < max && level <= 6) {
      level++;
      ch = state.src.charCodeAt(++pos);
    }

    if (level > 6) { return false; }

    if (silent) { return true; }

    // Let's cut tails like '    ###  ' from the end of string

    max = state.skipCharsBack(max, 0x20, pos); // space
    tmp = state.skipCharsBack(max, 0x23, pos); // #
    if (tmp > pos && state.src.charCodeAt(tmp - 1) === 0x20/* space */) {
      max = tmp;
    }

    state.line = startLine + 1;

    token        = state.push('heading_open', 'h' + String(level), 1);
    token.markup = '########'.slice(0, level);
    token.map    = [ startLine, state.line ];

    token          = state.push('inline', '', 0);
    token.content  = state.src.slice(pos, max).trim();
    token.map      = [ startLine, state.line ];
    token.children = [];

    token        = state.push('heading_close', 'h' + String(level), -1);
    token.markup = '########'.slice(0, level);

    return true;
  }

  md.block.ruler.at('heading', heading, {
    alt: [ 'paragraph', 'reference', 'blockquote' ]
  });
};