Generate Table of Contents Markdown code from HTML page

gentoc.js

// Run this in the console of the web browser
(function generateToC() {
  const headings = document.querySelectorAll('h1, h2, h3, h4, h5, h6');
  if (headings.length == 0)
    return;
  let minLevel = 6;
  for (let heading of headings) {
    let headingLevel = parseInt(heading.localName.charAt(1));
    if (headingLevel < minLevel)
      minLevel = headingLevel;
  }
  const toc = [];
  for (let heading of headings) {
    let anchor = heading.querySelector('a[href]');
    let indent = '';
    let headingLevel = parseInt(heading.localName.charAt(1));
    for (let level = headingLevel - minLevel; level > 0; level--) {
      indent += '  ';
    }
    toc.push(`${indent}* [${heading.textContent.trim().replace(/\s\s+/g, ' ')}](${anchor ? anchor.href : '#'+heading.id})`);
  }
  console.log(toc.join('\n'));
})()