Update the front-matter title property of Markdown files from the first heading title

update_front_matter_title_from_heading.js

const fs = require('node:fs');
const path = require('node:path');
const matter = require('gray-matter');
const MarkdownIt = require('markdown-it');
const MarkdownItFrontMatter = require('markdown-it-front-matter');

if (!matter || !MarkdownIt || !MarkdownItFrontMatter) {
  console.error('Module "gray-matter", "markdown-it", or "markdown-it-front-matter" not found. Run "npm install"');
  process.exit(1);
}

// Function to parse command line arguments
function parseArgs() {
  const args = process.argv.slice(2);
  const flags = {};
  const positionalArgs = [];

  args.forEach(arg => {
    if (arg.startsWith('--')) {
      const [flag, value] = arg.split('=');
      const flagName = flag.slice(2);
      flags[flagName] = value || true;
    } else if (arg.startsWith('-')) {
      const flagName = arg.slice(1);
      flags[flagName] = true;
    } else {
      positionalArgs.push(arg);
    }
  });

  return { flags, positionalArgs };
}

// Function to get the first heading of a Markdown file
function getFirstHeading(filePath) {
  // Read the file content
  const fileContent = fs.readFileSync(filePath, 'utf8');

  // Initialize Markdown-It
  const md = new MarkdownIt().use(MarkdownItFrontMatter, () => { });

  // Parse the Markdown content
  const tokens = md.parse(fileContent, {});

  // Find the first heading
  for (let token of tokens) {
    if (token.type === 'heading_open') {
      // The next token is the heading text
      const headingTextToken = tokens[tokens.indexOf(token) + 1];
      return headingTextToken.content;
    }
  }

  // No heading found
  return null;
}

// Function to read, edit, and write the front matter of a Markdown file
function editFrontMatter(filePath, flags) {
  // Read the file content
  const fileContent = fs.readFileSync(filePath, 'utf8');

  // Parse the front matter
  const parsedContent = matter(fileContent);

  // Modify the front matter (example: adding a new field 'modified' with the current date)
  const doWrite = !(flags['skip-existing'] && parsedContent.data.title)
  if (doWrite) {
    const firstHeading = getFirstHeading(filePath)
    if (firstHeading) {
      parsedContent.data.title = firstHeading;
    } else {
      parsedContent.data.title = 'TODO: please update with the correct title';
    }

    // Convert back to string with updated front matter
    const newContent = matter.stringify(parsedContent.content, parsedContent.data);

    // Write the new content back to the file
    fs.writeFileSync(filePath, newContent, 'utf8');
  }
}

// Function to iterate through a folder and process Markdown files
function processMarkdownFiles(folderPath, flags) {
  // Read the contents of the folder
  const files = fs.readdirSync(folderPath);

  // Iterate through each file/directory in the folder
  files.forEach(file => {
    const filePath = path.join(folderPath, file);

    // Check if the file is a directory
    if (fs.statSync(filePath).isDirectory()) {
      // Recursively process the subdirectory
      processMarkdownFiles(filePath, flags);
    } else if (path.extname(file) === '.md') {
      // If it's a Markdown file, edit its front matter
      console.log(`Processing file: ${filePath}`);
      editFrontMatter(filePath, flags);
    }
  });
}

async function main() {
  const { flags, positionalArgs } = parseArgs();

  // Sample script functionality based on parsed arguments
  if (flags.help) {
    console.log('Update the front-matter title of your Markdown files based on the first heading');
    console.log(`Usage: node ${path.relative(process.cwd(), __filename)} [options] MD_FOLDER_PATH`);
    console.log('Options:');
    console.log('  --help            Show this help message');
    console.log('  --skip-existing   Skip overwriting existing title front-matter');
    return;
  }

  if (positionalArgs.length < 1) {
    throw new Error('Please provide the markdown folder path');
  }

  const folderPath = positionalArgs[0];
  processMarkdownFiles(folderPath, flags);
}

main()
  .catch(console.error)

Installation:

1. In your Terminal app, create a new folder, cd into that new folder
2. Download the script into that folder, name it update_fm_in_md.js
3. Run npm init -y
4. Run npm install gray-matter markdown-it markdown-it-front-matter
5. Run node ./update_fm_in_md.js --help to see instructions