Date.prototype.setTime()

const launchDate = new Date("July 1, 1999, 12:00:00");
const futureDate = new Date();
futureDate.setTime(launchDate.getTime());

console.log(futureDate);
// Expected output: "Thu Jul 01 1999 12:00:00 GMT+0200 (CEST)"

const fiveMinutesInMillis = 5 * 60 * 1000;
futureDate.setTime(futureDate.getTime() + fiveMinutesInMillis);

console.log(futureDate);
// Expected output: "Thu Jul 01 1999 12:05:00 GMT+0200 (CEST)"
// Note: your timezone may vary