YYYY-MM-DD形式で取得
YYYY-MM-DD
var d = new Date('2020-01-01');
console.log(d);
console.log(d.toISOString().split('T')[0]);
=> 2020-01-01T00:00:00.000Z
2020-01-01
YYYY/MM/DD
var YYYY = d.getFullYear();
var d = new Date('2020-01-01');
var MM = ('0' + (d.getMonth() + 1)).slice(-2);
var DD = ('0' + d.getDate()).slice(-2);
console.log(YYYY + '/' + MM + '/' + DD);
=> 2020/01/01