Calculate Date

Before one day / After one day

const tmpDate = new Date();

> Mon Dec 24 2018 14:54:16 GMT+0900 (Korean Standard Time)

/// Before a Day

tmpDate.setDate(tmpDate.getDate() - 1);

> Sun Dec 23 2018 14:54:16 GMT+0900 (Korean Standard Time) {}

/// After a Day

tmpDate.setDate(tmpDate.getDate() + 1);

> Mon Dec 24 2018 14:54:16 GMT+0900 (Korean Standard Time)

Before two month / After four month

const tmpDate = new Date();

> Mon Dec 24 2018 14:56:20 GMT+0900 (Korean Standard Time)

/// Before a Day

tmpDate.setMonth(tmpDate.getMonth() - 2);

> Wed Oct 24 2018 14:56:20 GMT+0900 (Korean Standard Time)

/// After a Day

tmpDate.setMonth(tmpDate.getMonth() + 4);

> Sun Feb 24 2019 14:56:20 GMT+0900 (Korean Standard Time)

...etc...