その月のx番目のy曜日の日付を求める式を1行で書く - Qiita

function getDate(ordinalNumber, weekDay, date = new Date) { return ((7 * (ordinalNumber - 1) + 1) + (weekDay - new Date(date.getFullYear(), date.getMonth(), 1).getDay()) + (-(Math.sign(Math.sign(weekDay - new Date(date.getFullYear(), date.getMonth(), 1).getDay()) + 1) - 1) * 7)) * Math.sign(Math.sign(new Date(date.getFullYear(), date.getMonth() + 1, 0).getDate() - ((7 * (ordinalNumber - 1) + 1) +