var date = new Date();
var yearf = date.getFullYear(); // 2021
var year = date.getYear(); // 21
var month = date.getMonth() + 1; // +1을 해줘야합니다.
var day = date.getDate();
var hour = date.getHours();
var minute = date.getMinutes();
var second = date.getSeconds();
console.log( yearf + month + day + hour +minute + second );
// 결과
// 20210328174821
console.log( year + month + day + hour +minute + second );
// 결과
// 210328174821