Date.prototype.setDate()

const event = new Date("August 19, 1975 23:15:30");
event.setDate(24);
console.log(event.getDate());
// 予想される結果: 24
event.setDate(32);
// Only 31 days in August!
console.log(event.getDate());
// 予想される結果: 1

setDate(dateValue)

const theBigDay = new Date(1962, 6, 7, 12); // 1962-07-07 正午（月は 0 起点）
const theBigDay2 = new Date(theBigDay).setDate(24); // 1962-07-24
const theBigDay3 = new Date(theBigDay).setDate(32); // 1962-08-01
const theBigDay4 = new Date(theBigDay).setDate(22); // 1962-07-22
const theBigDay5 = new Date(theBigDay).setDate(0); // 1962-06-30
const theBigDay6 = new Date(theBigDay).setDate(98); // 1962-10-06
const theBigDay7 = new Date(theBigDay).setDate(-50); // 1962-05-11