99 bottles of beer

beersong.js

function beersong(count) {
  let startCount = count;
  let song = "";
  
  const countBottles = (c, cap) => {
    if (c === -1) return countBottles(startCount);
    if (c === 0) return (cap ? 'N' : 'n') + 'o more bottles';
    if (c === 1) return '1 bottle'
    return `${c} bottles`;
  }
  
  for (; count >= 0; --count) {
    song += `${countBottles(count, 1)} of beer on the wall, ${countBottles(count)} of beer.\n`;
    song += (count > 0) 
      ? "Take one down and pass it around, "
      : "Go to the store and buy some more, ";
    song += `${countBottles(count - 1)} of beer on the wall.\n\n`;
  }
  return song;
}

song = beersong(99);

pub.textContent = song;

beersong2.js

function beersong2(n) {
  const song = [];
  const startN = n;
  let verse = `{n} bottles of beer on the wall, {n} bottles of beer.
Take one down and pass it around, {o} bottles of beer on the wall.`;
  
  const count = x => x ? x : 'no more';
  
  for (; n >= 0; --n) {
    song.push(
      verse.replace(/{n}/g, count(n))
        .replace(/{o}/, n ? count(n - 1) : startN)
        .replace(/^n/, 'N')
        .replace(/1 bottles/g, '1 bottle')
        .replace((n === 0) && /Take.*,/, 'Go to the store and buy some more,')
    );
  }
  
  return song.join('\n\n');
}