markdownに今日の日付のタイトル(H1)をいれる

insertTodaysTitle.js

/**
 *
 * @param {string} markdownText
 * @param {Date} now
 */
function insertTodaysTitle(markdownText, now) {
  markdownText = markdownText.trim();
  const firstLine = markdownText.split("\n")[0].trim();

  const zerofill2 = (num) => ("0" + num).slice(-2);
  const month = zerofill2(now.getMonth() + 1);
  const date = zerofill2(now.getDate());
  const title = `# ${now.getFullYear()}-${month}-${date}`;

  if (firstLine.indexOf(title) === 0) {
    return markdownText;
  }

  return title + "\n\n\n" + markdownText.trim();
}