心配ゴム用 (^ω^)ニニニニニつ ビヨーン

gyazo.com

const buildBiyon = (max) => {
  let incr = 1;
  let count = 0;
  return () => {
    if (count === 1) {
      incr = 1;
    }
    if (count >= max) {
      incr = -1;
    }
    count = count + incr;
    return "ニ".repeat(count);
  };
};

(() => {
  const biyon = buildBiyon(5);
  setInterval(() => {
    history.replaceState({}, '', location.pathname+location.search+`#心配ゴム用 (^ω^)${biyon()}つ`)
  }, 100);
})()

See also blog.sushi.money