のすたろう、const isTodayBirthday = (

day: number | undefined,

month: number | undefined

): boolean => {

if (!day || !month) return false;

const now = new Date();

const thisYear = now.getFullYear();

const birthday = new Date(thisYear, month - 1, day); // ここで 2/29 は勝手に 3/1 になる

return (

birthday.getMonth() === now.getMonth() &&

birthday.getDate() === now.getDate()

);

};ってどう？